Publications
Note
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Journal Articles
- Wang, C., O’Loughlin, C. D., Bransby, M. F., Watson, P., Zhou, Z., Qi, Y., Tom, J. G., & Stanier, S. A. (2024). Permeable plate anchors: accelerating capacity gain in soft clay. Journal of Geotechnical and Geoenvironmental Engineering, 150(1), 04023123. https://doi.org/10.1061/JGGEFK.GTENG-11577Plate anchors have become an attractive technology for anchoring offshore floating facilities such as floating renewable energy devices because they provide high holding capacity relative to their dry weight. This allows for the use of smaller anchors (relative to a driven or suction-installed pile), which provide cost savings on production, transport, and installation. Loads delivered to the anchor via mooring lines may increase pore water pressure in fine-grained soils. This excess pore pressure will dissipate with time, resulting in a local increase in the undrained shear strength of the soil surrounding the anchor, increasing the capacity. There may be opportunities to consider these capacity increases if the consolidation process occurs over time periods that are short relative to the lifetime of the facility. This paper considers the use of drainage channels in a plate to make the anchor permeable and quicken consolidation times. Experimental data generated from model-scale experiments conducted in a geotechnical centrifuge show (for the anchor design tested) that excess pore pressure just above the anchor dissipated almost an order of magnitude faster for a permeable anchor, and that after full consolidation, the permeable anchor capacity was higher. The latter finding was not anticipated and is believed to be due to changes in load distribution resulting from the rapid reduction in negative excess pore pressure underneath the permeable anchor.
@article{wang_permeable_2024, author = {Wang, C. and O’Loughlin, C.D. and Bransby, M.F. and Watson, P. and Zhou, Z. and Qi, Y. and Tom, J.G. and Stanier, S.A.}, title = {Permeable plate anchors: accelerating capacity gain in soft clay}, journal = {Journal of Geotechnical and Geoenvironmental Engineering}, volume = {150}, number = {1}, pages = {04023123}, year = {2024}, doi = {10.1061/JGGEFK.GTENG-11577} } - Jia, T., Stanier, S. A., Watson, P., Feng, X., & Gourvenec, S. (2023). Theoretical framework for predicting accumulation of soil berms and peak sliding resistance for tolerably mobile foundations. Canadian Geotechnical Journal, available ahead of print online. https://doi.org/10.1139/cgj-2023-0138Tolerably mobile subsea foundations are designed to slide on the seabed to accommodate flowline thermal expansion and contraction, and are a potential alternative to conventional (fixed) foundations. During the periodic sliding events that occur during operation, soil berms form at the extremities of the foundation footprint. The size of the berm increases throughout the life-cycle of the foundation, leading to increasing peak sliding resistance. This may hinder mobility of foundation and overstress the pipeline connections that the foundation is designed to support. Equally, the berms may be relied on to reduce sliding and thus minimize settlement of the foundation, which can also overstress pipeline connections. This paper analyses the mechanism leading to berm accumulation and its mobilisation, also addressing periodic remoulding and reconsolidation of the sediment in the berm. A framework is proposed to predict the accumulation of soil berms and the resulting peak sliding resistance, and is validated by eight centrifuge model tests performed on a kaolin clay and a carbonate silt.
@article{jia_theoretical_2023, author = {Jia, T. and Stanier, S..A. and Watson, P. and Feng, X. and Gourvenec, S.}, title = {Theoretical framework for predicting accumulation of soil berms and peak sliding resistance for tolerably mobile foundations}, journal = {Canadian Geotechnical Journal}, volume = {{available ahead of print online}}, year = {2023}, doi = {10.1139/cgj-2023-0138} } - Singh, V., Mohr, H., Stanier, S. A., Bienen, B., & Randolph, M. F. (2023). Characterisation of interface friction strain-rate dependency of soft sediments at low stresses using a ring penetrometer. Géotechnique, available ahead of print online, 1–16. https://doi.org/10.1680/jgeot.22.00063The ring penetrometer is a shallow rotational penetrometer that has been developed to characterise the mechanical behaviour of surficial marine sediments. The strain-rate dependency of soils is crucial to the design of a wide range of offshore geotechnical infrastructure founded in the upper layers of the seabed (e.g. pipelines, cables and shallow foundations). This paper explores the potential application of a ring penetrometer test to measure the strain-rate dependency of the interface friction generated in soft soils at low stresses. Large-deformation numerical models of the test are developed using an elastoplastic constitutive model and a viscoplastic variant with strain softening. Using parameters representative of kaolin clay and a calcareous silt from an offshore location, the numerical analyses demonstrate a clear and measurable influence of both the viscous and strain-softening behaviours on the device–soil interface friction. These simulations were used to design suitable experimental protocols for multi-rate ring penetrometer tests, the results of which yielded a strain-rate dependency of 9–16% and 22–26% per log cycle in the kaolin clay and calcareous silt, respectively, which compare favourably with measurements derived from T-bar twitch experiments. Finally, models are presented that can be applied in the interpretation of varying-rate ring penetrometer test data for application in practice.
@article{singh_characterisation_2023, author = {Singh, V. and Mohr, H. and Stanier, S.A. and Bienen, B. and Randolph, M.F.}, title = {Characterisation of interface friction strain-rate dependency of soft sediments at low stresses using a ring penetrometer}, journal = {Géotechnique}, volume = {{available ahead of print online}}, pages = {1-16}, year = {2023}, doi = {10.1680/jgeot.22.00063} } - Jia, T., Stanier, S. A., Watson, P., Feng, X., & Gourvenec, S. (2023). The effect of soil type on the behaviour of a tolerably mobile subsea foundation. International Journal of Physical Modelling in Geotechnics, 23(6), 273–292. https://doi.org/10.1680/jphmg.22.00017Tolerably mobile subsea foundations may be used to replace conventional fixed mudmat foundations for pipeline infrastructure and are designed to slide on the seabed along with the connected pipeline, in order to accommodate thermally induced horizontal forces. This allows the size of the foundation and the resulting fabrication and installation costs to be substantially reduced. The performance of mobile foundations is explored in this paper through four centrifuge model tests on a normally consolidated or lightly over-consolidated reconstituted calcareous silt obtained from the Northwest Shelf of Western Australia. The results are compared to three existing tests performed on a kaolin clay. The results show that under typical periodic surface sliding and intervening rests, sliding resistance evolves within a cycle with resistance peaks evident at either end of the sliding footprint due to the formation of berms, and the residual resistance increasing with sliding cycles towards a drained state. Shear and consolidation-induced settlements accumulate with sliding cycles although at a reducing rate. The tests in the calcareous silt show higher normalised initial peak sliding resistance, a more dramatic loss and slower recovery of sliding resistance with cycles, and slower rate of decrease of incremental settlement compared with the response in kaolin clay.
@article{jia_effect_2023, author = {Jia, T. and Stanier, S..A. and Watson, P. and Feng, X. and Gourvenec, S.}, title = {The effect of soil type on the behaviour of a tolerably mobile subsea foundation}, journal = {International Journal of Physical Modelling in Geotechnics}, volume = {23}, number = {6}, pages = {273-292}, year = {2023}, doi = {10.1680/jphmg.22.00017} } - Singh, V., Stanier, S. A., Bienen, B., & Randolph, M. F. (2023). Calibration of strain-softening constitutive model parameters from full-field deformation measurements. Canadian Geotechnical Journal, 60(6), 817–833. https://doi.org/10.1139/cgj-2021-0342Many offshore geotechnical problems—such as cyclic T-bar penetration and lateral buckling of pipelines—are affected by the tendency of fine-grained soils to strain-soften due to remoulding. Careful calibration of the constitutive model parameters that control strain softening is essential for accurate simulation of these processes. This is usually achieved by matching constitutive model response with standard element test data, which implicitly assumes that homogeneous stress/strain fields exist within the sample. However, popular element test protocols (e.g., triaxial, simple shear) cannot apply sufficient deformation—at least as measured at the boundaries—to achieve fully remoulded conditions. This work explores the potential to determine strain-softening parameters experimentally, directly from image-based full-field deformation measurements and external loading data. Artificial data generated from finite element simulations of biaxial compression and T-bar penetration tests, using a non-locally regularised strain-softening constitutive model based on Modified Cam Clay, are then used to demonstrate the potential of the proposed technique. The results demonstrate significant potential for the application of the technique to identify constitutive parameters from full-field measurements even when polluted with modest measurement noise.
@article{singh_calibration_2023, author = {Singh, V. and Stanier, S.A. and Bienen, B. and Randolph, M.F.}, title = {Calibration of strain-softening constitutive model parameters from full-field deformation measurements}, journal = {Canadian Geotechnical Journal}, volume = {60}, number = {6}, pages = {817-833}, year = {2023}, doi = {10.1139/cgj-2021-0342} } - Soriano, C. Y. S., de Almeida, M. C. F., de Almeida, M. S. S., Madabhushi, S. P. G., & S.A., S. (2022). Centrifuge modeling of the seismic behavior of soft clay slopes. Journal of Geotechnical and Geoenvironmental Engineering, 148(11), 04022089. https://doi.org/10.1061/(ASCE)GT.1943-5606.0002884This paper presents the experimental results and analysis from two centrifuge experiments that simulated the seismic response of a gentle slope in soft clay. The two models consisted of a three-degree and a six-degree slope in soft clay, respectively, which are representative of typical slopes found on marine seabeds on the continental margins. The models were built in a laminar container in order to reproduce infinite slope boundary conditions. In-flight characterization investigations consisting of T-bar tests and air hammer tests were performed to obtain undrained shear strength profiles and shear wave velocities at various depths, respectively. A suite of earthquakes was applied, including sinusoidal waves and scaled real motions, in order to observe the response of the models in terms of the propagation of shear waves and the generation of lateral displacements at various depths in the slopes. The results showed that the model preparation approach ensures the repeatability of the experiments, enabling the evaluation of the impact of the slope angle on the seismic response of the gentle slopes studied. On average, the permanent displacements measured at the surface of the six-degree slope were three times greater than those measured at the top of the three-degree slope. In these slopes, nonlinear effects were observed in terms of the peak ground acceleration (PGA) that depended both on the slope angle and the intensity of shaking.
@article{soriano_centrifuge_2022, author = {Soriano, C.Y.S. and de Almeida, M.C.F and de Almeida, M.S.S. and Madabhushi, S.P.G. and S.A., Stanier}, title = {Centrifuge modeling of the seismic behavior of soft clay slopes}, journal = {Journal of Geotechnical and Geoenvironmental Engineering}, volume = {148}, number = {11}, pages = {04022089}, year = {2022}, doi = {10.1061/(ASCE)GT.1943-5606.0002884} } - Singh, V., Stanier, S. A., Bienen, B., & Randolph, M. F. (2022). A viscoplastic recoverable sensitivity model for fine-grained soils. Computers and Geotechnics, 147, 104725. https://doi.org/doi.org/10.1016/j.compgeo.2022.104725Full-flow penetrometer testing in fine-grained soils indicates that undrained shear strength decreases due to remoulding induced generation of excess pore pressures and increases due to strain rate effects and dissipation of excess pore pressures. This paper presents a viscoplastic strain-softening–hardening constitutive model that captures this duality of behaviour via non-local regularisation, strain rate dependency, and consolidation induced recovery of sensitivity. The model is based on Structured Modified Cam Clay and Perzyna’s overstress framework. Validation of the implementation is first demonstrated through simulation of constant rate of strain triaxial and oedometer compression tests performed on different clays. The model is then applied in large deformation finite element analyses of monotonic and variable rate T-bar penetration to demonstrate successful numerical implementation and its ability to simulate strain rate effects. Finally, the model is applied in the simulation of undrained cycles of penetration of a T-bar penetrometer in kaolin clay and a carbonate silt and compared with data from geotechnical centrifuge experiments. The results show that the model without sensitivity recovery significantly underestimates the consolidated-undrained resistance in both soils, suggesting that recoverable sensitivity is an aspect of behaviour that ought to be considered in the development of constitutive models for soft sensitive soils.
@article{singh_viscoplastic_2022, title = {A viscoplastic recoverable sensitivity model for fine-grained soils}, journal = {Computers and Geotechnics}, volume = {147}, pages = {104725}, year = {2022}, doi = {doi.org/10.1016/j.compgeo.2022.104725}, author = {Singh, V. and Stanier, S.A. and Bienen, B. and Randolph, M.F.}, keywords = {constitutive modelling, rate-dependency, strain-softening–hardening, sensitivity recovery, large deformation finite element analyses, T-bar penetration tests} } - Soriano, C. Y. C., de Almeida, M. C. F., Madabhushi, S. P. G., Stanier, S. A., de Almeida, M. S. S., Liu, H., & Borges, R. G. (2022). Seismic centrifuge modeling of a gentle slope of layered clay, including a weak layer. Geotechnical Testing Journal, 45(1). https://doi.org/doi.org/10.1520/GTJ20200236This article presents a model preparation methodology for simulating the seismic behavior of a gentle slope in clay with the presence of a soft, weak layer employing centrifuge testing. The model consisted of a three-layered slope of relatively soft clay with a 3° inclination, representative of Brazilian marine subsoils. In-flight characterization of the undrained shear strength and shear wave velocity profiles were achieved through T-bar penetrometer and air hammer tests. The model was subjected to a series of earthquake simulations at different amplitudes, and the response was tracked with accelerometers and displacement transducers. Additional data were obtained using a particle image velocimetry (PIV) methodology also described in this work. The results show that the proposed model preparation methodology enables the simulation of the strength contrast between the weak and relatively stronger surrounding layers using a laminar container. The additional displacement and acceleration data obtained from the PIV were in good agreement with the corresponding displacement transducer and accelerometer measurements. From the spectral analysis, a shift in the fundamental period was observed as the strain amplitude was increased, suggesting that strain rate effects mobilize higher stresses and a strength rate correction should be considered for the calibration of numerical models and comparison with existing methods for calculation of dynamic displacements in slopes.
@article{soriano_seismic_2021, author = {Soriano, C.Y.C. and de Almeida, M.C.F. and Madabhushi, S.P.G. and Stanier, S.A. and de Almeida, M.S.S. and Liu, H. and Borges, R.G.}, title = {Seismic centrifuge modeling of a gentle slope of layered clay, including a weak layer}, year = {2022}, doi = {doi.org/10.1520/GTJ20200236}, journal = {Geotechnical Testing Journal}, volume = {45}, number = {1} } - Mohr, H., Stanier, S. A., D.J., W., & Kuo, M. (2021). The variability of marine sediment erodibility with depth: centimetric scale effects detected from portable erosion flume tests. Applied Ocean Research, 113, 102721. https://doi.org/doi.org/10.1016/j.apor.2021.102721A portable erosion flume has been developed that is capable of estimating erosion threshold and erosion rate relationships for fine-grained specimens over the depth of a typical sample tube. This newly-designed apparatus is a recirculating flume capable of generating steady currents over the exposed section of the sample. In this paper, the erosion properties of two marine sediments have been determined and show a significant systematic variation with depth at centimetre scale that would have implications for the potential need for scour protection engineering. The tests showed that the critical erosion onset velocity doubled over the upper 200 mm of each sample, and the erosion rate fell by an order of magnitude. The increased erosion resistance with depth is consistent with the general trend of erodibility reducing with decreasing moisture content. Ignoring this depth effect when selecting design values of the erosion properties could lead to erroneous predictions of scour rate and extent around subsea structures, and unnecessary scour protection engineering costs.
@article{mohr_variability_2021, title = {The variability of marine sediment erodibility with depth: centimetric scale effects detected from portable erosion flume tests}, journal = {Applied Ocean Research}, volume = {113}, pages = {102721}, year = {2021}, issn = {0141-1187}, doi = {doi.org/10.1016/j.apor.2021.102721}, author = {Mohr, H. and Stanier, S.A. and D.J., White and Kuo, M.}, keywords = {portable erosion flume, erosion threshold, erosion rate, marine sediments, scour prediction, subsea pipelines} } - Singh, V., Stanier, S. A., Bienen, B., & Randolph, M. F. (2021). Modelling the behaviour of sensitive clays experiencing large deformations using non-local regularisation techniques. Computers and Geotechnics, 133, 104025. https://doi.org/doi.org/10.1016/j.compgeo.2021.104025This paper presents a methodology to simulate the strain-softening-hardening response of sensitive clays when subjected to extensive remoulding. A non-local strain-softening technique is implemented into the Abaqus Finite Element Analysis (FEA) software through its user defined material subroutine UMAT, in the form of a critical state based strain-softening constitutive model. For the comparison of conventional and non-local formulations, a series of analyses have been performed investigating mesh dependency issues and the validity of a simple softening-scaling rule for practical applications. The non-local model significantly reduces solution mesh-dependency for small-strain analyses of biaxial shear and updated Lagrangian analyses of buried pipe uplift. Finally, the non-local model is applied to simulate undrained cycles of penetration and the consolidated-undrained capacity of a T-bar in kaolin clay. This analysis highlights the limitations of the use of standard element tests (e.g. triaxial tests) to calibrate the model input parameters that control the strain-softening aspect of the constitutive law, and the need for a constitutive law that captures the partial recovery of sensitivity during consolidation.
@article{singh_modelling_2021, title = {Modelling the behaviour of sensitive clays experiencing large deformations using non-local regularisation techniques}, journal = {Computers and Geotechnics}, volume = {133}, pages = {104025}, year = {2021}, doi = {doi.org/10.1016/j.compgeo.2021.104025}, author = {Singh, V. and Stanier, S.A. and Bienen, B. and Randolph, M.F.}, keywords = {sensitive clays, strain localisation, non-local regularisation, large deformations, buried pipe uplift, T-bar penetration tests} } - Eichhorn, G. N., Bowman, A., Haigh, S. K., & Stanier, S. A. (2020). Low-cost digital image correlation and strain measurement for geotechnical applications. Strain, 56(6), e12348. https://doi.org/https://doi.org/10.1111/str.12348Abstract Particle image velocimetry (PIV), or digital image correlation (DIC), is a widely used technique to measure soil displacements and strains in small-scale geotechnical models. Arrays of single-board computers (SBCs) produced by Raspberry Pi, and their associated 8-MP cameras, are being used at the University of Cambridge to capture the images required for DIC analysis. This alternative to more expensive camera set-ups has numerous advantages. A single expensive and large camera can be replaced—at low cost—by multiple cameras, adding flexibility and affordability to any experimental set-up. Traditionally, the alignment of multiple cameras to each other and the referencing to a known coordinate system required painted or machined markers to be located on the observation windows through which the experiments are viewed. This can obstruct localised soil grain displacement measurements in those areas of the model where such markers are placed. To complement the Raspberry Pi camera system, a markerless calibration method was used during image acquisition. This paper outlines the set-up of four of these small computers and associated cameras, provides an overview of the use of the markerless referencing system and reviews two different experimental apparatus used to measure soil displacement and strain. When the cost of additional cabling, connectors and mounting hardware is considered for this system, the total cost to implement was approximately \125 USD per camera plus one-time costs of \175 USD for system peripherals, which represents outstanding value and enables practically all geotechnical laboratories to develop similar capabilities.
@article{eichorn_low_2020, author = {Eichhorn, G.N. and Bowman, A. and Haigh, S.K. and Stanier, S.A.}, title = {Low-cost digital image correlation and strain measurement for geotechnical applications}, journal = {Strain}, volume = {56}, number = {6}, pages = {e12348}, keywords = {binary fiducial marker, ChArUco, digital image correlation (DIC), Raspberry PI, single-board computer (SBC), soil displacement, soil strain}, doi = {https://doi.org/10.1111/str.12348}, year = {2020} } - Teng, Y., Stanier, S. A., & Gourvenec, S. M. (2020). Mechanisms beneath rectangular shallow foundations on sands: vertical loading. Géotechnique, 70(12), 1083–1093. https://doi.org/10.1680/jgeot.18.P.058This paper details analysis of deformation behaviour of silica and carbonate sands under a rectangular foundation subject to uniaxial vertical load based on results from a series of centrifuge model tests. A multiscale particle image velocimetry/digital image correlation (PIV/DIC) technique was used to record and analyse the foundation tests with high resolution and measurement precision. Cone penetrometer and pressuremeter tests provide in situ soil characterisation of the tested sand sample in the centrifuge environment. The soil behaviour is analysed through foundation load–settlement response and the observed soil deformation measurements. Different soil deformation mechanisms and strain behaviours were observed in the different sands tested, and the particle shape effect is considered, with data from scanning electron microscopy, to explain the differences. The results and analyses contribute towards better understanding of different soil behaviours under shallow foundations in different sands.
@article{teng_mechanisms_2020, author = {Teng, Y. and Stanier, S.A. and Gourvenec, S.M.}, title = {Mechanisms beneath rectangular shallow foundations on sands: vertical loading}, journal = {Géotechnique}, volume = {70}, number = {12}, pages = {1083-1093}, year = {2020}, doi = {10.1680/jgeot.18.P.058} } - Zhou, Z., O’Loughlin, C. D., White, D. J., & Stanier, S. A. (2020). Improvements in plate anchor capacity due to cyclic and maintained loads combined with consolidation. Géotechnique, 70(8), 732–749. https://doi.org/10.1680/jgeot.19.TI.028Plate anchor technology is an efficient solution for mooring offshore floating facilities for oil and gas or renewable energy projects. When used with a taut mooring, the anchor is typically subjected to a maintained load component and intermittent episodes of cyclic loading throughout the design life. These loads, and the associated shearing, remoulding and consolidation processes, cause changes in the anchor capacity, particularly in soft, fine-grained soils. The changing anchor capacity affects the mooring performance by changing the safety margin and also the overall system reliability. In this paper the changing anchor capacity in reconstituted, normally consolidated natural carbonate silt was assessed through a series of beam centrifuge tests on horizontally loaded circular plate anchors. The results demonstrate that full consolidation under a typical maintained load leads to a 50% gain in the anchor capacity, and subsequent cyclic loading and reconsolidation can triple this increase. An effective stress framework based on critical state concepts is employed to explain and support the experimental observations. This study shows that, when viewed from a whole-life reliability perspective, maintained and cyclic loading provide a long-term enhancement of anchor capacity in soft, fine-grained soils. This beneficial effect is currently overlooked in design practice, but can be predicted using the framework shown here, which can form the basis for a digital twin that monitors the through-life integrity of a plate anchor.
@article{zhou_improvements_2020, author = {Zhou, Z. and O'Loughlin, C.D. and White, D.J. and Stanier, S.A.}, title = {Improvements in plate anchor capacity due to cyclic and maintained loads combined with consolidation}, journal = {Géotechnique}, volume = {70}, number = {8}, pages = {732-749}, year = {2020}, doi = {10.1680/jgeot.19.TI.028} } - Ragni, R., Bienen, B., O’Loughlin, C. D., Stanier, S. A., Cassidy, M. J., & Morgan, N. (2020). Observations of the effects of a clay layer on suction bucket installation in sand. Journal of Geotechnical and Geoenvironmental Engineering, 146(5), 04020020. https://doi.org/10.1061/(ASCE)GT.1943-5606.0002217Suction buckets are becoming established as a viable foundation solution for offshore wind turbines. In sand, suction-induced seepage flow reduces effective stresses at the skirt tips, which decreases penetration resistance. However, layered seabeds are often encountered in areas of offshore wind farm development. The effect of the presence of a clay layer on the suction-induced seepage flow in the sand layer is not well understood. Therefore in this study, the effects of a clay layer on suction bucket installation in dense sand was investigated. This was achieved by analyzing images of a half-bucket installed against a Perspex window. The images were captured during tests performed in a geotechnical centrifuge, such that the stress levels are realistic and relevant to field conditions. Installations in sand-over-clay were unproblematic and characterized by deformation of the sand-clay interface, with no clear interruption of the seepage flow. Installations in clay-over-sand were also successful. Uplift of the clay plug was identified as the mechanism to transfer suction to the underlying sand, creating seepage flow and thus facilitating further skirt penetration rather than terminating the installation.
@article{ragni_observations_2020, author = {Ragni, R. and Bienen, B. and O’Loughlin, C.D. and Stanier, S.A. and Cassidy, M.J. and Morgan, N.}, title = {Observations of the effects of a clay layer on suction bucket installation in sand}, journal = {Journal of Geotechnical and Geoenvironmental Engineering}, volume = {146}, number = {5}, pages = {04020020}, year = {2020}, doi = {10.1061/(ASCE)GT.1943-5606.0002217} } - O’Loughlin, C. D., Zhou, Z., Stanier, S. A., & White, D. J. (2020). Load-controlled cyclic T-bar tests: a new method to assess effects of cyclic loading and consolidation. Géotechnique Letters, 10(1), 7–15. https://doi.org/10.1680/jgele.19.00030Full-flow T-bar and ball penetrometer tests are often used to measure intact and remoulded soil strengths, with the latter determined after several large-amplitude displacement cycles. In offshore design, the remoulded soil strength is often the governing design parameter during installation of subsea infrastructure, while a ‘cyclic strength’ applies for the less severe operational cyclic loading. This paper utilises T-bar penetrometer tests to measure both remoulded and cyclic strengths, where the latter is determined by way of a new test protocol involving cycles between load rather than displacement limits. The tests use kaolin clay and a reconstituted carbonate silt and involve three cyclic phases with intervening consolidation periods. The results demonstrate the important and beneficial role of consolidation, with the loss in strength due to remoulding sometimes surpassed by the strength recovery from consolidation. The most significant gains in strength, to 2·5 times the initial value, were measured in the load-controlled cyclic tests. These data demonstrate a novel way to characterise undrained cyclic strength, taking advantage of consolidation to reduce conservatism.
@article{oloughlin_load_2020, author = {O'Loughlin, C. D. and Zhou, Z. and Stanier, S. A. and White, D. J.}, title = {Load-controlled cyclic T-bar tests: a new method to assess effects of cyclic loading and consolidation}, journal = {Géotechnique Letters}, volume = {10}, number = {1}, pages = {7-15}, year = {2020}, doi = {10.1680/jgele.19.00030} } - Schneider, M. A., Stanier, S. A., White, D. J., & Randolph, M. F. (2020). Shallow penetrometer tests: theoretical and experimental modelling of penetration and dissipation stages. Canadian Geotechnical Journal, 57(4), 568–579. https://doi.org/10.1139/cgj-2018-0656Shallow penetrometers are devices that penetrate into and measure the properties of surficial offshore sediments via multi-phase tests involving penetration, dissipation, and rotation stages. In fine-grained soils such as silts and clays, these testing stages yield undrained strength, consolidation, and friction properties relevant to subsea pipeline and shallow foundation design. This paper describes toroid and hemiball devices of the scale for use in box-core samples and associated interpretation methods for the penetration and dissipation stages. The aim of the paper is to provide all tools needed to design and interpret these tests. New large-deformation finite element (LDFE) dissipation solutions are presented, which can be used for back-analysis of the dissipation stage. Results of an extensive laboratory proof testing exercise in kaolin clay, for both the hemiball and toroid penetrometers, are also reported. These results highlight the potential of the two devices to quickly and economically assess strength and consolidation characteristics of fine-grained sediments in box-core samples recovered to the deck of a site investigation vessel.
@article{schneider_penetration_2020, author = {Schneider, M.A. and Stanier, S.A. and White, D.J. and Randolph, M.F.}, title = {Shallow penetrometer tests: theoretical and experimental modelling of penetration and dissipation stages}, journal = {Canadian Geotechnical Journal}, volume = {57}, number = {4}, pages = {568-579}, year = {2020}, doi = {10.1139/cgj-2018-0656} } - Schneider, M. A., Stanier, S. A., White, D. J., & Randolph, M. F. (2020). Shallow penetrometer tests: theoretical and experimental modelling of the rotation stage. Canadian Geotechnical Journal, 57(4), 580–594. https://doi.org/10.1139/cgj-2018-0657Shallow penetrometers are a new type of device that measures the properties of surficial offshore sediments via multi-phase tests involving penetration, dissipation, and rotation stages. In fine-grained soils such as silts and clays, these testing stages yield properties relevant to subsea pipeline and shallow foundation design; namely, undrained strength, consolidation, and interface friction. This paper describes the fundamentals of the rotation stage, including models required for data interpretation, encompassing both a total and an effective stress framework. Additionally, new relationships to evaluate the pore pressure scaling factor, which is a key interpretation parameter required to convert discrete measurements of pore pressure on the penetrometers to an average pore pressure over the contact area, are developed based on large-deformation finite element simulations. Results from an experimental campaign using kaolin clay samples are presented, illustrating the potential of the devices to rapidly and repeatably measure interface friction properties of fine-grained sediments offshore. The results compare well with comparative measures obtained from shear box tests conducted at similarly low effective stress levels. Recommendations regarding future in situ applications are given at end of the paper.
@article{schneider_rotation_2020, author = {Schneider, M.A. and Stanier, S.A. and White, D.J. and Randolph, M.F.}, title = {Shallow penetrometer tests: theoretical and experimental modelling of the rotation stage}, journal = {Canadian Geotechnical Journal}, volume = {57}, number = {4}, pages = {580-594}, year = {2020}, doi = {10.1139/cgj-2018-0657} } - Hu, P., Cassidy, M. J., Sahdi, F., & Stanier, S. A. (2020). Breakout force required for jack-up spudcan extraction from sand-over-clay seabeds. Soils and Foundations, 60(2), 413–424. https://doi.org/10.1016/j.sandf.2020.03.004Spudcan retrieval from clay soils remains a major concern offshore as the extraction force required to overcome suction and soil resistance often exceeds the pulling capacity available on the mobile jack-up, causing extensive delays. Although methods to calculate extraction resistance have been recently suggested for seabeds of pure clay, to date there is no guidance available for the commonly encountered sand-over-clays. Based on failure mechanisms observed in half-spudcan visualisation tests, and calibrated against an extensive geotechnical centrifuge database of precisely measured extractions, this paper presents a method for calculating the force required to extract the spudcan foundations of mobile jack-up platforms after they have penetrated through a sand layer into underlying clay. Complexities, such as the strength degradation and strength recovery of the underlying clay soil, that occurs during spudcan installation and jack-up operations, are accounted for. Validation of the proposed method is demonstrated by retrospective prediction of the centrifuge testing database. The method outlined will allow operators of jack-up platforms to assess the extraction force prior to jack-up installation and to plan operational scenarios based on seabed conditions.
@article{hu_breakout_2020, title = {Breakout force required for jack-up spudcan extraction from sand-over-clay seabeds}, journal = {Soils and Foundations}, volume = {60}, number = {2}, pages = {413-424}, year = {2020}, doi = {10.1016/j.sandf.2020.03.004}, author = {Hu, P. and Cassidy, M.J. and Sahdi, F. and Stanier, S.A.}, keywords = {centrifuge modelling, clays, sands, consolidation, spudcan foundation} } - Ragni, R., Bienen, B., Stanier, S. A., O’Loughlin, C. D., & Cassidy, M. J. (2019). Observations during suction bucket installation in sand. International Journal of Physical Modelling in Geotechnics, 1–18. https://doi.org/10.1680/jphmg.18.00071Suction buckets represent a viable solution as foundations for offshore wind turbines. Installation in sand is relatively straightforward, albeit with limited understanding of the resulting changes in soil state. This paper describes an experimental methodology that allows for visualisation and quantification of changes in soil state during suction bucket installation, validated in sand. Insights obtained from particle image velocimetry analyses, performed on images of a half-bucket installing against a Perspex window taken in a geotechnical centrifuge are discussed. Compared with the initial self-weight penetration, the deformation mechanism governing the suction-assisted phase shows a preference for the soil below the skirt tips to move inwards and upwards inside the bucket. The installation process is responsible for changes in relative density and permeability within the bucket. In these experiments, the majority of the soil plug heave can be attributed to the soil displaced inwards by the advancing skirts, with a minor contribution caused by dilation. The confidence in the experimental methodology provided through the results of suction bucket installation in sand discussed herein now enables suction bucket installation in more complex seabeds to be investigated.
@article{ragni_observations_2019, title = {Observations during suction bucket installation in sand}, doi = {10.1680/jphmg.18.00071}, journal = {International Journal of Physical Modelling in Geotechnics}, author = {Ragni, R. and Bienen, B. and Stanier, S. A. and O'Loughlin, C. D. and Cassidy, M. J.}, month = jan, year = {2019}, keywords = {DIC, PIV, caisson}, pages = {1--18} } - O’Loughlin, C. D., Cocjin, M. L., Gourvenec, S. M., & Stanier, S. A. (2019). A simple approach to multi-degree-of-freedom loading in a geotechnical centrifuge. Geotechnical Testing Journal, 42(5), 20180037. https://doi.org/10.1520/GTJ20180037This article considers an alternative approach for multiplanar loading and multi-degree-of-freedom movement in geotechnical centrifuge model tests. The multi-degree-of-freedom loading system allows for vertical load control on the vertical axis and either displacement or load control on the two horizontal axes, while allowing rotation about these axes. The system is described in detail, and the system performance is validated through results from a centrifuge test comparing observed results with analytical and numerical solutions. The validation of thesystem considers a mudmat foundation under large amplitude lateral displacement, where two displacement degrees-of-freedom and two rotational degrees-of-freedom were of interest. However, the apparatus is versatile and can be used for testing other foundation types or pipelines, with up to six degrees-of-freedom.
@article{oloughlin_simple_2019, title = {A simple approach to multi-degree-of-freedom loading in a geotechnical centrifuge}, volume = {42}, doi = {10.1520/GTJ20180037}, number = {5}, journal = {Geotechnical Testing Journal}, author = {O’Loughlin, Conleth D. and Cocjin, Michael L. and Gourvenec, Susan M. and Stanier, S. A.}, month = sep, year = {2019}, pages = {20180037} } - Stanier, S. A., & White, D. J. (2018). Enhancement of bearing capacity from consolidation: due to changing strength or failure mechanism? Géotechnique, 69(2), 166–173. https://doi.org/10.1680/jgeot.17.T.030Bearing capacity of shallow foundations is higher following preload (or self-weight)-induced consolidation because the soil strength changes, and perhaps because the failure mechanism changes. Previous studies have illustrated this effect by plotting or predicting changes in either bearing capacity factor or strength. In this study, the relative contribution of these two effects is explored. This is achieved by formalising a definition of bearing capacity factor, which is described in terms of the average strength mobilised in the deformation mechanism at failure. Using the alternative definition of bearing capacity factor, the gain in foundation capacity is shown to be almost entirely due to changes in soil strength, rather than bearing capacity factor, which remains largely unaffected by the strength gains. This observation should encourage future studies into consolidated bearing capacity to present gains in capacity in terms of changes in mobilised strength rather than changes in bearing capacity factors, and supports the use of prediction methods that focus on defining the change in soil strength.
@article{stanier_enhancement_2018, title = {Enhancement of bearing capacity from consolidation: due to changing strength or failure mechanism?}, volume = {69}, doi = {10.1680/jgeot.17.T.030}, number = {2}, urldate = {2019-02-18}, journal = {Géotechnique}, author = {Stanier, S. A. and White, D. J.}, month = mar, year = {2018}, keywords = {bearing capacity, consolidation}, pages = {166--173} } - Schneider, M. A., Stanier, S. A., Chatterjee, S., White, D. J., & Randolph, M. F. (2018). The parkable piezoprobe for determining cv and strength – modelling and interpretation methods. Géotechnique, 1–12. https://doi.org/10.1680/jgeot.18.P.004The parkable piezoprobe is a site investigation tool for measuring the coefficient of consolidation, in situ offshore, at shallow embedment depths. The device applies a similar bearing pressure to subsea infrastructure so it reaches a comparable self-weight penetration when ‘parked’ at the seabed, representative of an unburied pipeline. Instrumentation on the device allows the dissipation of penetration-induced excess pore pressure to be recorded at various locations on the surface. From these dissipation responses the coefficient of consolidation can be inferred, which is a key parameter in the design of many offshore structures founded in surficial soil, such as pipelines or shallow foundations. The intent is that this device is deployed from a seabed frame, while other activities such as penetrometer testing or sampling take place in parallel. This paper presents robust interpretation methods for the parkable piezoprobe by using a combination of centrifuge experiments and large deformation finite-element analyses. The centrifuge tests demonstrate that the penetration response of the parkable piezoprobe is adequately captured by existing bearing capacity models, allowing the optimum device weight to be identified. A comprehensive interpretation method is then developed for the dissipation stage. This yields accurate estimates of the coefficient of consolidation, even for cases where there is no prior knowledge of the soil parameters or the depth to which the device embeds under its own self-weight.
@article{schneider_parkable_2018, title = {The parkable piezoprobe for determining cv and strength – modelling and interpretation methods}, doi = {10.1680/jgeot.18.P.004}, urldate = {2019-02-18}, journal = {Géotechnique}, author = {Schneider, M. A. and Stanier, S. A. and Chatterjee, S. and White, D. J. and Randolph, M. F.}, month = may, year = {2018}, keywords = {consolidation, shallow penetrometer, offshore site investgation}, pages = {1--12} } - Ullah, S. N., Stanier, S. A., Hu, Y., & White, D. J. (2017). Foundation punch-through in clay with sand: analytical modelling. Géotechnique, 67(8), 672–690. https://doi.org/10.1680/jgeot.16.P.101Severe punch-through of jack-up rig foundations can occur due to the presence of a stronger sand layer in a bed of relatively soft clay. Analytical estimation of the bearing capacity and leg load–penetration response on such multi-layer stratigraphies is challenging. Accurate mechanism-based models need to be established in each of the layers involved and the effects of the mechanisms in each of the layers on the response in the other layers must be captured. Based on the recently developed failure stress-dependent punch-through models for sand–clay stratigraphies, an extended model is proposed for clay–sand–clay stratigraphies. Half-spudcan particle image velocimetry centrifuge tests and full-spudcan centrifuge tests are used in developing and validating the extended model. The centrifuge test results were discussed in a companion paper and this paper focuses on the analytical developments and prediction assessment. Both spudcan peak resistance (qpeak) and spudcan punch-through depth (dpunch) can be estimated using the model. The predictions by the extended model and by the current industry guidelines are compared against the centrifuge test data. The extended model proposed in this paper outperforms the approaches suggested in the guidelines. An advantage of the proposed approach is that it can be used for either sand–clay or clay–sand–clay scenarios and exhibits excellent performance compared to the model testing dataset considered in this work for both cases. The resulting penetration resistance model is a useful design tool for routine punch-through risk assessment.
@article{ullah_foundation_2017, title = {Foundation punch-through in clay with sand: analytical modelling}, volume = {67}, doi = {10.1680/jgeot.16.P.101}, number = {8}, journal = {Géotechnique}, author = {Ullah, S. N. and Stanier, S. A. and Hu, Y. and White, D. J.}, month = jan, year = {2017}, keywords = {centrifuge modelling, punch-through, spudcan, analytical modelling}, pages = {672--690} } - Ullah, S. N., Stanier, S. A., Hu, Y., & White, D. J. (2017). Foundation punch-through in clay with sand: centrifuge modelling. Géotechnique, 67(10), 870–889. https://doi.org/10.1680/jgeot.16.P.100This paper is concerned with the vertical penetration resistance of conical spudcan and flat footings in layered soils. Centrifuge tests are reported for a clay bed with strength increasing with depth interbedded with dense and medium dense sand. Both non-visualising (full-model) and visualising (half-model) tests were conducted with high-quality digital images captured and analysed using the particle image velocimetry technique for the latter. The load–displacement curves often show a reduction in resistance on passing through the sand layers, which creates a risk of punch-through failure for the foundations when supporting a jack-up drilling unit. For a given foundation, the peak punch-through capacity (qpeak) is dependent on the thickness of both the overlying clay and the sand layer. The failure mechanism associated with the peak resistance in the sand layer involves entrapment of a thin band of top clay above the sand layer that subsequently shears along an inclined failure surface before being pushed into the underlying clay. The top clay height when normalised by the foundation diameter affects the soil failure pattern in this layer and along with the sand layer thickness controls the severity of the punch-through failure (i.e. the additional penetration before the resistance returns to the peak value). Comparisons are made with current industry guidelines for predicting qpeak and the risk of punch-through failure for sand overlying clay. These methods are shown to be conservative in their prediction of qpeak but inconsistent in predicting punch-through.
@article{ullah_foundation_2017-1, title = {Foundation punch-through in clay with sand: centrifuge modelling}, volume = {67}, doi = {10.1680/jgeot.16.P.100}, number = {10}, journal = {Géotechnique}, author = {Ullah, S. N. and Stanier, S. A. and Hu, Y. and White, D. J.}, month = mar, year = {2017}, keywords = {centrifuge modelling, punch-through, spudcan}, pages = {870--889} } - Hambleton, J. P., & Stanier, S. A. (2017). Predicting wheel forces using bearing capacity theory for general planar loads. International Journal of Vehicle Performance, 3(1), 71–88. https://doi.org/10.1504/IJVP.2017.081276This paper assesses the applicability of bearing capacity theory for evaluating the forces generated on wheels operating on clay under steady rolling conditions. Considering advances in bearing capacity theory, in particular the interaction diagrams developed for general loading, a theoretical model for computing the horizontal force or torque from fundamental input parameters such as the vertical force (weight), wheel diameter, and undrained shear strength of the soil is presented. The predictions are compared with existing analytical solutions and data from laboratory testing, and reasonable agreement is demonstrated. The newly proposed model provides a means to predict wheel forces analytically under any operating condition (driven, braked, or towed), provided the contact length and so-called contact angle, which defines the position of the contact interface, can be estimated. The model provides a rigorous, convenient framework for evaluating wheel forces under arbitrary loading and enables a natural physical interpretation of the mobility problem.
@article{hambleton_predicting_2017, title = {Predicting wheel forces using bearing capacity theory for general planar loads}, volume = {3}, doi = {10.1504/IJVP.2017.081276}, number = {1}, journal = {International Journal of Vehicle Performance}, author = {Hambleton, J. P. and Stanier, S. A.}, month = jan, year = {2017}, keywords = {clay, bearing capacity, wheel mobility, undrained}, pages = {71--88} } - Ragni, R., Wang, D., Mašín, D., Bienen, B., Cassidy, M. J., & Stanier, S. A. (2016). Numerical modelling of the effects of consolidation on jack-up spudcan penetration. Computers and Geotechnics, 78, 25–37. https://doi.org/10.1016/j.compgeo.2016.05.002The paper addresses the issue of consolidation around jack-up foundations in carbonate silty clay. The problem is tackled with the numerical implementation of a hypoplastic model for structured clays, within the framework of large deformation finite element analyses. Coupled analyses are simulated to account for excess pore pressure build-up and dissipation, while sensitivity parameters capture the effects of remoulding. The model implementation is described first, followed by its validation against centrifuge data. The paper concludes with a detailed discussion of beneficial or detrimental effects on spudcan capacity upon re-penetration, depending on the consolidation and soil sensitivity characteristics.
@article{ragni_numerical_2016, title = {Numerical modelling of the effects of consolidation on jack-up spudcan penetration}, volume = {78}, doi = {10.1016/j.compgeo.2016.05.002}, journal = {Computers and Geotechnics}, author = {Ragni, R. and Wang, D. and Mašín, D. and Bienen, B. and Cassidy, M. J. and Stanier, S. A.}, month = sep, year = {2016}, keywords = {numerical modelling, bearing capacity, hypoplasticity, consolidation, sensitivity, spudcan}, pages = {25--37} } - Stanier, S. A., Dijkstra, J., Leśniewska, D., Hambleton, J. P., White, D. J., & Muir Wood, D. (2016). Vermiculate artefacts in image analysis of granular materials. Computers and Geotechnics, 72, 100–113. https://doi.org/10.1016/j.compgeo.2015.11.013Some reported analyses of images of deforming granular materials have generated surprising vermiculate strain features which are difficult to reconcile with the mechanics of deformation of granular matter. Detailed investigation using synthetic images and improved processing of images of laboratory experiments indicates that such features can emerge as a consequence of the image acquisition (sensor, contrast, resolution), the subsequent image correlation implementation, and the user’s choice of processing parameters. The two principal factors are: (i) the texture and resolution of the images and (ii) the algorithm used to achieve sub-pixel displacement resolution. Analysis of the images using a sub-pixel interpolation algorithm that is more robust than that used originally eliminates the vermiculate features for images with moderate resolution and texture. However, erroneous features persist in images with low resolution and poor texture. Guidance is provided on ways in which such artefacts can be avoided through improved experimental and image analysis techniques.
@article{stanier_vermiculate_2016, title = {Vermiculate artefacts in image analysis of granular materials}, volume = {72}, doi = {10.1016/j.compgeo.2015.11.013}, language = {en}, journal = {Computers and Geotechnics}, author = {Stanier, S. A. and Dijkstra, J. and Leśniewska, D. and Hambleton, J. P. and White, D. J. and Muir Wood, D.}, month = feb, year = {2016}, keywords = {CV, deformation, DIC, image-based, PIV, vermiculation}, pages = {100--113} } - Teng, Y., Stanier, S. A., & Gourvenec, S. M. (2016). Synchronised multi-scale image analysis of soil deformations. International Journal of Physical Modelling in Geotechnics, 17(1), 53–71. https://doi.org/10.1680/jphmg.15.00058New apparatus and techniques for performing synchronised multi-scale particle image velocimetry or digital image correlation (PIV/DIC) soil deformation measurements have been developed. A central camera records a full field of view (FoV) of the model capturing the ‘macro’ deformation mechanism and the boundaries of the model. Simultaneously, an adjacent slave camera records a subset of the full FoV capturing the ‘micro’ soil response in a region of special interest, such as under the corner of footing. The ‘micro’ FoV images have higher resolution in terms of particle/pixel size ratio (d/p), resulting in the ability to measure localised deformations that are invisible to lower resolution images. Recommendations are made with respect to appropriate subset size and spacing for high-resolution images. A photogrammetric correction process requiring a small number of static control points is proposed and the performance is validated against a conventional photogrammetric calibration utilising a large array of static control points. Lastly, results from a validation experiment are presented comparing the PIV/DIC output from the ‘macro’ and ‘micro’ FoV, illustrating that: (a) the photogrammetric correction method proposed is robust and (b) that there has been an improvement in spatial resolution of the strain measurements that can be obtained through the ‘micro’ FoV camera.
@article{teng_synchronised_2016, title = {Synchronised multi-scale image analysis of soil deformations}, volume = {17}, doi = {10.1680/jphmg.15.00058}, number = {1}, journal = {International Journal of Physical Modelling in Geotechnics}, author = {Teng, Y. and Stanier, S. A. and Gourvenec, S. M.}, month = aug, year = {2016}, keywords = {foundation, DIC, PIV}, pages = {53--71} } - Ullah, S. N., Hu, Y., Stanier, S. A., & White, D. J. (2016). Lateral boundary effects in centrifuge foundation tests. International Journal of Physical Modelling in Geotechnics, 17(3), 144–160. https://doi.org/10.1680/jphmg.15.00034Large deformation finite-element analyses were conducted to explore the effect of the container lateral boundary in centrifuge tests where a large offshore foundation is tested. A spudcan foundation, typically used to support jack-up drilling rigs, was penetrated into uniform clay, uniform sand and sand overlying clay stratigraphies under rough and smooth lateral boundary conditions. The effect that the proximity of the container lateral boundary has on the measured load–penetration response is quantified. The boundary impact varies with the soil profile and boundary roughness, and for sand-only or sand-over-clay conditions the required separation between the foundation and the container boundary is far greater than in clay-only conditions. In most cases, during large penetration of the spudcan foundation, the largest influence from the lateral boundary was on peak resistance, and diminished during the subsequent deeper penetration. For practical use, a centrifuge container design chart is proposed to check whether the dimensions are adequate for the foundation and model size to be used in an experiment. It is shown that the results from many earlier studies could have been potentially influenced by container boundary effects.
@article{ullah_lateral_2016, title = {Lateral boundary effects in centrifuge foundation tests}, volume = {17}, doi = {10.1680/jphmg.15.00034}, number = {3}, journal = {International Journal of Physical Modelling in Geotechnics}, author = {Ullah, S. N. and Hu, Y. and Stanier, S. A. and White, D. J.}, month = apr, year = {2016}, keywords = {centrifuge modelling, spudcan, boundary effects, LDFE}, pages = {144--160} } - Stanier, S. A., Blaber, J., Take, W. A., & White, D. J. (2015). Improved image-based deformation measurement for geotechnical applications. Canadian Geotechnical Journal, 53(5), 727–739. https://doi.org/10.1139/cgj-2015-0253This paper describes and benchmarks a new implementation of image-based deformation measurement for geotechnical applications. The updated approach combines a range of advances in image analysis algorithms and techniques best suited to geotechnical applications. Performance benchmarking of the new approach has used a series of artificial images subjected to prescribed spatially varying displacement fields. An improvement by at least a factor of 10 in measurement precision is achieved relative to the most commonly used particle image velocimetry (PIV) approach for all deformation modes, including rigid-body displacements, rotations, and strains (compressive and shear). Lastly, an example analysis of a centrifuge model test is used to demonstrate the capabilities of the new approach. The strain field generated by penetration of a flat footing and an entrapped sand plug into an underlying clay layer is computed and compared for both the current and updated algorithms. This analysis demonstrates that the enha..., Le présent article décrit et évalue la mise en œuvre récente d’une nouvelle méthode de mesure de déformation basée sur des images et applicable au domaine de la l’ingénierie géotechnique. Cette nouvelle méthode combine une série d’améliorations apportées aux algorithmes et techniques d’analyse d’images spécialement adaptés au domaine de l’ingénierie géotechnique. L’évaluation des performances de cette nouvelle méthode a été réalisée à l’aide d’une série d’images artificielles soumises à des champs de déplacement définis et variant dans l’espace. Une amélioration de la précision des mesures d’un facteur au moins égal à dix est obtenue si l’on utilise la nouvelle méthode plutôt que la méthode la plus souvent employée de la vélocimétrie par images de particules (VIP), et ce pour tous les modes de déformation, y compris les déplacements, rotations et déformations (par compression ou par cisaillement) de corps rigides. Enfin, on se sert d’un exemple d’analyse d’un essai sur modèle en centrifugeuse pour montrer...
@article{stanier_improved_2015, title = {Improved image-based deformation measurement for geotechnical applications}, volume = {53}, doi = {10.1139/cgj-2015-0253}, number = {5}, journal = {Canadian Geotechnical Journal}, author = {Stanier, S. A. and Blaber, J. and Take, W.A. and White, D.J.}, month = oct, year = {2015}, keywords = {deformation, DIC, image-based, PIV, GeoPIV}, pages = {727--739} } - Hu, P., Wang, D., Stanier, S. A., & Cassidy, M. J. (2015). Assessing the punch-through hazard of a spudcan on sand overlying clay. Géotechnique, 65(11), 883–896. https://doi.org/10.1680/jgeot.14.P.097A complete analytical method to describe the full load-penetration resistance profile of a mobile jack-up spudcan footing penetrating a sand over clay stratigraphy is described. It is based on both large deformation finite-element analyses and geotechnical centrifuge experiments. The coupled Eulerian–Lagrangian (CEL) approach is used to accommodate the large deformations of a spudcan footing penetrating sand overlying clay. Modified Mohr–Coulomb and Tresca models describe the sand and clay behaviour, with modifications accounting for the effects of strain softening on the response of the soil. The CEL results are shown to match centrifuge tests well, allowing the numerical study to be extended parametrically, and with confidence, to cover the range of layer geometries, sand relative densities and footing shapes that are of practical interest to offshore jack-ups. The results are used to (a) assess the performance of an existing model to predict the peak resistance in the sand layer (extending its range of application to medium dense to dense sands and to conical footings of angle 0° to 21°), and (b) develop an expression for the bearing capacity factor when the footing penetrates into the underlying clay. Using the analytical formulas proposed, retrospective simulations of centrifuge tests show that the method provides a reasonable estimate of the peak punch-through load, the behaviour in the underlying clay, as well as the punch-through distance; the latter being a basic reflection of the severity of a potential punch-through failure.
@article{hu_assessing_2015, title = {Assessing the punch-through hazard of a spudcan on sand overlying clay}, volume = {65}, doi = {10.1680/jgeot.14.P.097}, number = {11}, journal = {Géotechnique}, author = {Hu, P. and Wang, D. and Stanier, S. A. and Cassidy, M. J.}, month = oct, year = {2015}, keywords = {centrifuge modelling, punch-through, spudcan}, pages = {883--896} } - Bienen, B., Ragni, R., Cassidy, M. J., & Stanier, S. A. (2015). Effects of consolidation under a penetrating footing in carbonate silty clay. Journal of Geotechnical and Geoenvironmental Engineering, 141(9), 04015040. https://doi.org/10.1061/(ASCE)GT.1943-5606.0001339The effects of consolidation under a footing are generally viewed as beneficial due to the resulting increased capacity. Consolidation may also be actively sought because it minimizes footing embedment, which can be critical for the installation of mobile offshore jack-ups because available leg length is limited. However, it can also set the platform footing up to subsequently punch through the strengthened zone, with potentially serious consequences. The problem is complex due to the three-dimensional nature of consolidation. Further, footing penetration leaves the soil above heavily remolded and generates large excess pore pressures below, such that the soil state even prior to consolidation is significantly altered from its in situ conditions. This study has taken an experimental approach to investigate the effects of consolidation around a footing penetrating into carbonate silty clay and, following detailed discussion of the response, offers a framework to predict the changes to the load-penetration curve.
@article{bienen_effects_2015, title = {Effects of consolidation under a penetrating footing in carbonate silty clay}, volume = {141}, doi = {10.1061/(ASCE)GT.1943-5606.0001339}, number = {9}, journal = {Journal of Geotechnical and Geoenvironmental Engineering}, author = {Bienen, B. and Ragni, R and Cassidy, M. J. and Stanier, S. A.}, month = sep, year = {2015}, keywords = {punch-through, consolidation, spudcan}, pages = {04015040} } - Stanier S. A., & White D. J. (2015). Shallow penetrometer penetration resistance. Journal of Geotechnical and Geoenvironmental Engineering, 141(3), 04014117. https://doi.org/10.1061/(ASCE)GT.1943-5606.0001257Shallow penetrometers—such as the hemiball and toroid—were conceived as potential in situ testing devices with the ability to measure: (1) soil strength parameters during vertical penetration, (2) soil consolidation characteristics during dissipation tests postpenetration, and (3) interface friction during torsional loading. Knowledge of the response of soil to such tests is critical to the design of subsea pipelines and the ability to measure the response of soil to all three types of test using a single device in situ from a mobile testing platform, such as a remotely operated vehicle (ROV), would be highly advantageous. Potential benefits of the employment of such devices could include significant time and cost savings and improved spatial measurement density, since more tests could be conducted along the route of a pipeline if an ROV is used as a mobile in situ testing platform. This paper presents an assessment of the ability of the hemiball and toroid to measure soil strength parameters directly from their response to vertical penetration. A large deformation finite-element approach was employed to model the penetration process and initial simulations were validated against small-strain analyses published in the literature. A comprehensive parametric study was then conducted investigating the impact on normalized penetration resistance of soil unit weight, shear strength gradient and penetrometer-soil interface friction. A forward model was derived from the parametric analyses and its inverse performance (i.e., the ability to infer soil parameters from force-displacement response) was assessed using additional large deformation analyses with randomly assigned material parameters within realistic bounds. Both variants of shallow penetrometer investigated are found to be well suited to inferring soil strength parameters directly from their response to vertical penetration.
@article{stanier_shallow_2015, title = {Shallow penetrometer penetration resistance}, volume = {141}, doi = {10.1061/(ASCE)GT.1943-5606.0001257}, number = {3}, journal = {Journal of Geotechnical and Geoenvironmental Engineering}, author = {{Stanier S. A.} and {White D. J.}}, month = mar, year = {2015}, keywords = {penetration testing, shallow penetrometer}, pages = {04014117} } - Hu, P., Stanier, S. A., Wang, D., & Cassidy, M. J. (2015). Effect of footing shape on penetration in sand overlying clay. International Journal of Physical Modelling in Geotechnics, 16(3), 119–133. https://doi.org/10.1680/jphmg.15.00013This paper reports on a series of centrifuge model tests investigating the effect of shape on the penetration resistance of spudcan and conical footings on sand overlying clay. The effect of footing shape and geometry on single-layer soil has been studied intensely. However, there is still limited understanding for conical footings on sand over clay. In the present study, digital images were captured during penetration of various shapes of half-footing held against a transparent window of a strongbox. The images were then analysed using particle image velocimetry techniques. Experimental evidence has shown that, irrespective of the conical angle of the underside within the range of 7–21°, when the footing penetrates through sand into an underlying clay layer: (a) accumulated radial and deviatoric shear strains along the future failure surface counteract each other, resulting in similar peak resistance in the sand layer and (b) a trapped sand plug of constant height is pushed into the underlying clay layer. These observations serve to justify the previously proposed methods for predicting the full penetration resistance profile on sand overlying clay, which is required to predict the potential for, and severity of, punch-through failure.
@article{hu_effect_2015, title = {Effect of footing shape on penetration in sand overlying clay}, volume = {16}, doi = {10.1680/jphmg.15.00013}, number = {3}, journal = {International Journal of Physical Modelling in Geotechnics}, author = {Hu, P. and Stanier, S. A. and Wang, D. and Cassidy, Mark J.}, month = oct, year = {2015}, keywords = {centrifuge modelling, punch-through, spudcan, shape effects}, pages = {119--133} } - Hu, P., Stanier, S. A., Wang, D., & Cassidy, M. J. (2015). A comparison of full profile prediction methods for a spudcan penetrating sand overlying clay. Géotechnique Letters, 5(3), 131–139. https://doi.org/10.1680/jgele.15.00051Spudcans are the traditional footings used for offshore mobile jack-up rigs. However, the installation of spudcans in sand overlying clay may lead to punch-through failure, which can cause serious damage to the jack-up rig and endanger personnel. This article compares three new methods proposed in the literature and an interpretation of the International Organization for Standardization (ISO) guideline for predicting the full penetration resistance profile. The penetration resistance profile for each of the methods is characterised by two key calculations: the peak resistance in the sand and the bearing capacity within the underlying clay. The punch-through distance – an indicator of the potential for and severity of punch-through failure – is estimated from these calculations. In comparison with 71 geotechnical centrifuge tests, the ISO guideline provides poor predictions, consistently underestimating the peak resistance in the sand and the underlying bearing capacity in the clay. Although all three of the new methods provide a superior response, by assessing the accuracy, scatter and geometric skew of the predictions, two of the methods are shown to be biased in at least one of the key calculations used to define the penetration resistance profile, thus producing bias in the prediction of the punch-through distance. However, one method yields largely unbiased predictions.
@article{hu_comparison_2015, title = {A comparison of full profile prediction methods for a spudcan penetrating sand overlying clay}, volume = {5}, doi = {10.1680/jgele.15.00051}, number = {3}, journal = {Géotechnique Letters}, author = {Hu, P. and Stanier, S. A. and Wang, D. and Cassidy, M. J.}, month = sep, year = {2015}, keywords = {centrifuge modelling, punch-through, spudcan}, pages = {131--139} } - Stanier, S. A., White, D. J., Chatterjee, S., Brunning, P., & Randolph, M. F. (2015). A tool for ROV-based seabed friction measurement. Applied Ocean Research, 50, 155–162. https://doi.org/10.1016/j.apor.2015.01.016This paper describes a new device for measuring seabed sliding resistance in situ, and provides an associated interpretation procedure. The device is designed to use a work class ROV as a testing platform to allow measurements to be obtained without use of a specialized geotechnical survey platform. The measurements are to assist pipeline design or analysis of the sliding resistance of other on-bottom infrastructure such as anchor chains. The device has been trialled using three tools: a flat plate, a cylindrical pipe section and a length of chain. The tools are dragged axially along the seabed using the ROV thrusters or a separate hydraulic actuator. An interpretation technique has been developed to estimate the passive resistance mobilized by the faces of the tools to eliminate end effects and to account for shape effects such as wedging. Onshore-trial tests were performed in a bed of dry sand. The individual tools exhibited different overall coefficients of friction, but the back-analysis method yielded equal interface friction angles acting on all three devices, indicating internal consistency. The interface friction angle also matched shear box test results. These outcomes confirm the correct operation of the device in drained seabed conditions, and yield useful information on the sliding resistance of pipes and chains. In addition, the back-analysis method allows measurements from one shape of tool to be used to estimate the response of other objects.
@article{stanier_tool_2015, title = {A tool for {ROV}-based seabed friction measurement}, volume = {50}, doi = {10.1016/j.apor.2015.01.016}, journal = {Applied Ocean Research}, author = {Stanier, S. A. and White, D. J. and Chatterjee, S. and Brunning, P. and Randolph, M. F.}, month = mar, year = {2015}, keywords = {ROV, friction, measurement, mooring chain, pipeline}, pages = {155--162} } - Hu, P., Stanier, S. A., Cassidy, M. J., & Wang, D. (2014). Predicting peak resistance of spudcan penetrating sand overlying clay. Journal of Geotechnical and Geoenvironmental Engineering, 140(2), 04013009. https://doi.org/10.1061/(ASCE)GT.1943-5606.0001016Accurately predicting peak penetration resistance qpeak during spudcan installation into sand overlying clay is crucial to an offshore mobile jack-up industry still suffering regular punch-through failures. This paper describes a series of spudcan penetration tests performed on medium-loose sand overlying clay and compares the response to existing centrifuge data from tests performed on dense sand overlying clay. Together these data demonstrate that punch-through is a potential problem for both dense and loose sand overlying clay soil stratigraphies. Using this experimental database, a failure-stress-dependent model has been modified to account for the embedment depth, and the depth of occurrence of qpeak is shown to be a function of the sand thickness Hs. The model then was recalibrated, taking these findings into account, for a larger range of material properties and ratios of sand thickness to spudcan diameter (Hs/D). Finally, the performance of the modified and recalibrated model is verified by comparing its predictions with those calculated using current guidelines. The comparisons show that the modified model yields more accurate predictions of qpeak over the range of Hs/D ratios of practical interest, which when used in practice will potentially mitigate the risk of unexpected punch-through on sand overlying clay stratigraphies.
@article{hu_predicting_2014, title = {Predicting peak resistance of spudcan penetrating sand overlying clay}, volume = {140}, doi = {10.1061/(ASCE)GT.1943-5606.0001016}, number = {2}, journal = {Journal of Geotechnical and Geoenvironmental Engineering}, author = {Hu, P. and Stanier, S. A. and Cassidy, M. J. and Wang, D.}, month = feb, year = {2014}, keywords = {centrifuge modelling, punch-through, spudcan}, pages = {04013009} } - Hu, P., Wang, D., Cassidy, M. J., & Stanier, S. A. (2014). Predicting the resistance profile of a spudcan penetrating sand overlying clay. Canadian Geotechnical Journal, 51(10), 1151–1164. https://doi.org/10.1139/cgj-2013-0374Assessment of the risk of punch-through failure of spudcan foundations on sand overlying clay requires prediction of the full penetration resistance profile, from touchdown and through punch-through to equilibrium of the vertical resistance at depth in the underlying clay layer. This study uses the Coupled Eulerian–Lagrangian approach, a large deformation finite element analysis method, to model the complete penetration resistance profile of a spudcan on sand overlying clay. The sand is modeled using the Mohr–Coulomb model, while the clay is modeled using a modified Tresca model to account for strain softening. The numerical method is then used to simulate a series of spudcan penetration tests, performed in a geotechnical centrifuge, on medium dense sand overlying clay. The punch-through behavior observed in the experiments is replicated, and the penetration resistance profiles from numerical analyses are generally a reasonable match to the experimental measurements. The influences of the sand layer heigh..., L’évaluation du risque de rupture en perforation de fondations de type caisson de support sur de l’argile couverte de sable nécessite la prédiction du profil complet de résistance à la pénétration, de la mise en place au sol à la perforation et jusqu’à l’équilibre de la résistance verticale en profondeur dans la couche d’argile sous-jacente. Cette étude utilise l’approche Eulérienne-Lagrangienne couplée, une méthode d’analyse par éléments finis à grande déformation, pour modéliser le profil complet de résistance à la pénétration d’un caisson de support sur de l’argile couverte de sable. Le sable est modélisé à l’aide du modèle Mohr-Coulomb, tandis que l’argile est modélisée à l’aide d’un modèle Tresca modifié pour considérer l’adoucissement des déformations. Le modèle numérique est ensuite utilisé pour simuler une série d’essais de pénétration de caissons de support, réalisés dans une centrifugeuse géotechnique, sur de l’argile couverte de sable moyen dense. Le comportement en perforation observé dans les...
@article{hu_predicting_2014-1, title = {Predicting the resistance profile of a spudcan penetrating sand overlying clay}, volume = {51}, doi = {10.1139/cgj-2013-0374}, number = {10}, journal = {Canadian Geotechnical Journal}, author = {Hu, P. and Wang, D. and Cassidy, M. J. and Stanier, S. A.}, month = may, year = {2014}, keywords = {centrifuge modelling, punch-through, spudcan}, pages = {1151--1164} } - Stanier, S. A., Ragni, R., Bienen, B., & Cassidy, M. J. (2014). Observing the effects of sustained loading on spudcan footings in clay. Géotechnique, 64(11), 918–926. https://doi.org/10.1680/geot.14.P.003Spudcan foundations of mobile jack-up rigs are penetrated into the seabed under seawater ballast preload, which is shed prior to rig operations commencing. During pauses in the installation process and during operation, soil beneath the spudcan foundations stiffens and strengthens due to consolidation. On the application of further loading or during spudcan extraction, this causes increased resistance, which in extremis can result in punch-though type failure. This note reports results from a series of experiments with particle image velocimetry measurements that were performed in a drum centrifuge to facilitate observation of the effects of a load-hold period on the soil movements around a model spudcan during subsequent further loading. The results show that the dimensionless load-hold period dominates the enhancement in the penetration resistance, due to significantly more soil being mobilised following a long load-hold period. These observations might be useful to (a) predict the enhancement in bearing capacity factor due to a load-hold period during installation or operation and (b) predict the footing extraction resistance during jack-up re-deployment.
@article{stanier_observing_2014, title = {Observing the effects of sustained loading on spudcan footings in clay}, volume = {64}, doi = {10.1680/geot.14.P.003}, number = {11}, journal = {Géotechnique}, author = {Stanier, S. A. and Ragni, R. and Bienen, B. and Cassidy, M. J.}, month = nov, year = {2014}, keywords = {DIC, PIV, punch-through, consolidation, spudcan}, pages = {918--926}, file = {Stanier et al. - 2014 - Observing the effects of sustained loading on spud.pdf:/home/sas229/Zotero/storage/GE459ZDP/Stanier et al. - 2014 - Observing the effects of sustained loading on spud.pdf:application/pdf} } - Ullah, S. N., Hu, Y., White, D. J., & Stanier, S. A. (2014). LDFE study of bottom boundary effect in foundation model tests. International Journal of Physical Modelling in Geotechnics, 14(3), 80–87. https://doi.org/10.1680/ijpmg.14.00004Centrifuge model tests of deeply penetrating foundations have been widely used to assess the vertical bearing response, particularly in relation to the installation of spudcan foundations that support offshore drilling rigs. The potential influence of boundary effects owing to the proximity of these large foundations to the rigid base of the model container has not been previously addressed. In this study, large deformation finite-element (LDFE) analyses were conducted to assess the extent of the bottom boundary influence zone. Various foundation diameters were considered, with soil samples of sand overlying clay and uniform clay. The sand plug developed beneath the foundation is a major contributary factor to the boundary effect problem. The boundary effect is increased for sand over clay conditions, where a sand plug is entrapped beneath the foundation. The LDFE results were utilised to predict the thickness of the entrapped sand plug for different geometry and soil strength conditions. The results are distilled into a simple relationship that can be used to ascertain the bottom boundary influence zone when planning physical model tests and reinterpreting previous studies. The boundary influence zone predicted by the LDFE analysis agreed well with a corresponding centrifuge test.
@article{ullah_ldfe_2014, title = {{LDFE} study of bottom boundary effect in foundation model tests}, volume = {14}, doi = {10.1680/ijpmg.14.00004}, number = {3}, journal = {International Journal of Physical Modelling in Geotechnics}, author = {Ullah, S. N. and Hu, Y. and White, D. J. and Stanier, S. A.}, month = sep, year = {2014}, keywords = {centrifuge modelling, spudcan, boundary effects, LDFE}, pages = {80--87} } - Hambleton, J. P., Stanier, S. A., Gaudin, C., & Todeshkejoei, K. (2014). Analysis of installation forces for helical piles in clay. Australian Geomechanics Journal, 49(7), 73–79.Installation forces play a central role in the design and performance of helical piles, especially since the installation torque is often used as an indicator of the pile’s ultimate capacity. This paper presents an analytical model for predicting the installation torque for single-helix piles in clay. As an extension of a recent study by the authors, the proposed model considers not only the forces occurring on the helical plates but also the shear stresses generated along the shaft, both of which impact the installation forces. The model yields a straightforward expression that relates installation torque to the undrained shear strength of the soil, embedment depth, helix diameter and pitch, shaft diameter, crowd (axial) force, and adhesion coefficient along the shaft. The influence of these factors on the installation torque, as well as the “capacity-to-torque ratio” used to infer capacity from the installation, is assessed through a sensitivity analysis. Some level of validation is provided through a comparison with empirical capacity-to-torque ratios, and the sensitivity analysis reveals factors that are neglected in empirical models but nevertheless have a significant influence.
@article{hambleton_analysis_2014, title = {Analysis of installation forces for helical piles in clay}, volume = {49}, author = {Hambleton, J. P. and Stanier, S. A. and Gaudin, C and Todeshkejoei, K}, year = {2014}, journal = {Australian Geomechanics Journal}, keywords = {clay, helical piles, analytical modelling}, number = {7}, pages = {73--79} } - Stanier, S. A., & White, D. J. (2013). Improved image-based deformation measurement in the centrifuge environment. Geotechnical Testing Journal, 36(6), 20130044. https://doi.org/10.1520/GTJ20130044This paper describes a new apparatus and techniques for performing deformation measurements using particle image velocimetry in the centrifuge environment. The new system includes camera, lighting, and control equipment that facilitates image capture at least 30 times faster than that in legacy systems. Methods for optimizing the addition of artificial seeding on the exposed plane of a geotechnical model are also set out. These techniques ensure that the precision of the deformation calculations is optimized even in models with multiple layers of different soils, fully harnessing the method’s capabilities. An example application of a flat footing penetrating sand overlying clay is used to illustrate the performance of the equipment and the artificial seeding optimization technique. Deformation fields at the point of peak resistance during punchthrough are presented in the form of vector fields, normalized displacement contours, and shear strain contours. It is shown that the advances in equipment and artificial seeding allow both macroscopic and grain-scale deformation features to be identified. These analyses highlight not only the benefits of the new technology, but also the need for carefully optimized experimental procedures to maximize the measurement precision.
@article{stanier_improved_2013, title = {Improved image-based deformation measurement in the centrifuge environment}, volume = {36}, issn = {01496115}, doi = {10.1520/GTJ20130044}, number = {6}, journal = {Geotechnical Testing Journal}, author = {Stanier, S. A. and White, D. J.}, month = nov, year = {2013}, keywords = {deformation, DIC, image-based, PIV}, pages = {20130044} } - Stanier, S. A., Black, J. A., & Hird, C. C. (2013). Modelling helical screw piles in clay and design implications. Proceedings of ICE - Geotechnical Engineering, 167, 447–460. https://doi.org/10.1680/geng.13.00021Helical screw piles are a popular solution for relatively low-capacity, removable or recyclable foundations supporting road and rail signage or similar light structures. When specifying a helical screw pile, a designer must choose the active length and the helical plate spacing ratio, which are governed by the number, spacing and size of the individual helices. This paper presents an investigation using transparent synthetic soil and particle image velocimetry to observe the failure of helical screw piles with helical plate spacing ratios of 1·5–3 and active lengths up to three times the diameter. For the geometries and properties examined, capacity is shown to be a function of active length and the dominant failure mechanism is characterised by the formation of a cylindrical failure surface. A simple analytical model is developed and used to assess the impact of different design methodologies on immediate displacements under loading. A traditional ‘permissible stress’ method is shown to be conservative, whereas modern ‘partial factor’ methods are more economical and lead to greater immediate displacements for a given design load. Designers using modern ‘partial factor’ approaches, such as Eurocode 7, might benefit from specifying a helical plate spacing ratio of less than 1·5 to maximise the stiffness of the response to axial loading and minimise the immediate displacements experienced upon application of working loads.
@article{stanier_modelling_2013, title = {Modelling helical screw piles in clay and design implications}, volume = {167}, doi = {10.1680/geng.13.00021}, journal = {Proceedings of ICE - Geotechnical Engineering}, author = {Stanier, S. A. and Black, J. A. and Hird, C. C.}, month = nov, year = {2013}, keywords = {transparent soil, helical piles, eurocodes}, pages = {447--460} } - Stanier, S. A., & Tarantino, A. (2013). An approach for predicting the stability of vertical cuts in cohesionless soils above the water table. Engineering Geology, 158, 98–108. https://doi.org/10.1016/j.enggeo.2013.03.012Temporary vertical excavations in cohesionless (granular) soils pose a problem for conventional ‘two-phase’ soil mechanics theory since non-zero collapse height is not predicted using the classical ‘dry/saturated’ shear strength criterion, given that cohesionless soils above the water table are assumed to be dry. An extension of the classical shear strength equation to account for the effect of matric suction on the effective stress in partially saturated soil is presented here that is incorporated into the bound theorems of plasticity. A simple validation experiment is reported to test the concept following which, a case study is presented that explores the extent to which matric suction and its impact on shear strength can explain the large safe vertical cut height that is often observed in cohesionless pozzolan deposits in the field. Lastly, the impact of rainfall events and subsequent ponded infiltration is investigated using a very simple analytical technique based on the classical Terzaghi consolidation solution. The research presented here gives practitioners with no particular expertise in the mechanics of unsaturated soil, techniques to assess the stability of geostructures involving unsaturated cohesionless soils that are based on simple calculation techniques taught in undergraduate courses.
@article{stanier_approach_2013, title = {An approach for predicting the stability of vertical cuts in cohesionless soils above the water table}, volume = {158}, doi = {10.1016/j.enggeo.2013.03.012}, journal = {Engineering Geology}, author = {Stanier, S. A. and Tarantino, Alessandro}, month = may, year = {2013}, keywords = {excavation, laboratory tests, limit analysis, partial saturation, shear strength, suction}, pages = {98--108} } - Stanier, S. A., Black, J. A., & Hird, C. C. (2012). Enhancing accuracy and precision of transparent synthetic soil modelling. International Journal of Physical Modelling in Geotechnics, 12, 162–175. https://doi.org/10.1680/ijpmg.12.00005Over recent years non-intrusive modelling techniques have been developed to investigate soil-structure interaction problems of increasingly complex geometry. This paper concerns the development of a small-scale, 1 g, modelling technique using a transparent analogue for soil with particle image velocimetry for internal displacement measurement. Larger model geometry achieved in this research using fine-grained transparent synthetic soils has led to an increased need for rigorous photogrammetric correction techniques. A correction framework, based upon a modified version of the pinhole camera model, is presented that corrects for lens and camera movement induced errors as well as scaling from image space to object space. An additional statistical approach is also developed to enhance the system precision, by minimising the impact of increased non-coplanarity between the photogrammetry control plane and the target plane. The enhanced data correction and statistical precision is demonstrated using a case study examining the failure mechanism around a double helical screw pile installed in transparent synthetic soil representative of a soft clay.
@article{stanier_enhancing_2012, title = {Enhancing accuracy and precision of transparent synthetic soil modelling}, volume = {12}, doi = {10.1680/ijpmg.12.00005}, journal = {International Journal of Physical Modelling in Geotechnics}, author = {Stanier, S. A. and Black, J. A. and Hird, C. C.}, month = dec, year = {2012}, keywords = {transparent soil, helical piles}, pages = {162--175}, file = {Stanier et al. - 2012 - Enhancing accuracy and precision of transparent sy.pdf:/home/sas229/Zotero/storage/2GQU2UPP/Stanier et al. - 2012 - Enhancing accuracy and precision of transparent sy.pdf:application/pdf} }
Conference Proceedings
- Peters, T., van Eekelen, S., Anastasopoulos, I., Korre, E., Stanier, S. A., Viggiani, G. M. B., Askarinejad, A., Muraro, S., Zlender, B., Lenart, S., Estaire, J., Santana, M., Thorel, L., Bessman, E., Le, T. M. H., l’Heureux, S., Zachert, H., Eitner, M.-A. B., Yankulova, A., & Singh, M. (2022). GEOLAB: integrating and advancing Europe’s physical modelling facilities. ICPMG 2022, Proceedings of the 10th International Conference on Physical Modelling in Geotechnics, Daejon, South Korea , 140–144.The critical infrastructure of Europe is currently facing multifaceted challenges. The GEOLAB research infrastructure comprises 12 unique facilities in Europe for studying ground behavior and its interaction with structural elements and the environment. The aim of GEOLAB is to integrate and advance these national facilities into a onestop-shop for performing excellent physical modelling research and innovation for enhancing the resilience of critical infrastructure. The joint research activities are advancing the capabilities of the GEOLAB facilities beyond present state-of-the-art. During transnational access, experiments proposed by outside user groups are carried out.
@inproceedings{peters_geolab_2022, title = {GEOLAB: integrating and advancing Europe's physical modelling facilities}, booktitle = {ICPMG 2022, {Proceedings} of the 10th {International} {Conference} on {Physical} {Modelling} in {Geotechnics}, Daejon, South Korea }, author = {Peters, T. and van Eekelen, S. and Anastasopoulos, I. and Korre, E. and Stanier, S.A. and Viggiani, G.M.B. and Askarinejad, A. and Muraro, S. and Zlender, B. and Lenart, S. and Estaire, J. and Santana, M. and Thorel, L. and Bessman, E. and Le, T.M.H and l'Heureux, S. and Zachert, H. and Eitner, M-A.B. and Yankulova, A. and Singh, M.}, year = {2022}, keywords = {research infrastructure, data, physical modelling, numerical modelling, critical infrastructure}, pages = {140--144} } - Characterisation of near-surface sediments using a blend of vertical and shallow rotational penetrometers. (2022). Cone Penetration Testing 2022, Bologna, Italy, 259–266.The mechanical properties of near-surface sediments – to a depth of approximately half a metre – are relevant to the design of cables, pipelines and other shallowly-embedded infrastructure, as well as benthic habitat characterisation. For this depth of interest, vertically-pushed penetrometers – such as the cone, T-bar or ball – can be supplemented by shallow rotational devices such as the toroid or hemiball. In this paper, we report vertical and shallow rotational penetrometer test procedures and show results obtained in pro ject conditions on natural soil samples. By combining these different penetrometers, a wider and more reliable set of mechanical properties – spanning strength and consolidation behaviour – can be obtained, compared to conventional practice. The paper concludes with practical advice on testing protocols and interpretation methods to best characterise the shallow seafloor, including the use of novel shallow penetrometers.
@inproceedings{white_characterisation_2022, title = {Characterisation of near-surface sediments using a blend of vertical and shallow rotational penetrometers}, booktitle = {Cone {Penetration} {Testing} 2022, Bologna, Italy}, author = {}, year = {2022}, keywords = {shallow penetrometers, site investigation, shallow}, pages = {259--266} } - Hambleton, J. P., & Stanier, S. A. (2019). Linking the installation response of screw piles to soil strength and ultimate capacity. Proc. of the 1st International Symposium on Screw Piles for Energy Applications, Dundee 2019, 638–647.A perceived advantage of screw-type foundations is the ability infer aspects of foundation performance from quantities measured or observed during installation, especially the installation torque. A particular concept widely used in practice is to correlate installation torque to ultimate capacity. This notion has proven useful as a field verification technique despite the absence of validated models that relate key variables of interest, such as installation torque, axial (crowd) force, geometrical parameters, and soil strength. This paper considers previous work by the co-authors and collaborators on analytical, numerical, and physical modelling of screw piles to relate the quantities measured or controlled during installation (e.g., installation torque) to the ultimate capacity and soil strength. Attention is given to saturated clay as a particular soil type amenable to simplified analysis. An analytical model for a single-helix pile is considered as a means of directly relating the ultimate capacity and undrained shear strength to the installation torque, crowd force, plate pitch, plate diameter, shaft diameter, installation depth, and surface roughness. The connection between the installation variables and ultimate capacity—and the sensitivity to crowd force in particular, a quantity that is typically not measured during field installations—is also discussed. The theoretical predictions are compared against data obtained from small-scale laboratory experiments that suggest the installation torque relates to the remolded strength of the soil.
@inproceedings{hambleton_linking_2019, title = {Linking the installation response of screw piles to soil strength and ultimate capacity}, booktitle = {{Proc}. of the 1st {International} {Symposium} on {Screw} {Piles} for {Energy} {Applications}, {Dundee} 2019}, publisher = {Dundee University}, author = {Hambleton, J. P. and Stanier, S. A.}, year = {2019}, keywords = {screw piles, helical anchors, installation, torque-capacity correlation, modeling, experiments}, pages = {638--647} } - Randolph, M. F., Stanier, S. A., O’Loughlin, C. D., Chow, S., Bienen, B., Doherty, J. P., Mohr, H., Ragni, R., Schneider, M. A., White, D. J., & Schneider, J. (2018). Penetrometer equipment and testing techniques for offshore design of foundations, anchors and pipelines. Cone Penetration Testing 2018: Proceedings of the 4th International Symposium on Cone Penetration Testing (CPT’18), Delft, The Netherlands, 21-22 June 2018, 3–23.This paper attempts to categorise geotechnical field site characterisation tools in a hierarchical manner, as appropriate for the progression from initial surveys to detailed geotechnical design of specific infrastructure. In general, the hierarchy reflects more the sophistication, and hence cost, of the field tools, although small-scale tools developed to explore box core samples are something of an exception, with the potential for high quality data at low cost. These ideas are explored in the context of modern developments in equipment and methods of deployment, and in the manner in which the data may be used efficiently in design.
@inproceedings{randolph_penetrometer_2018, title = {Penetrometer equipment and testing techniques for offshore design of foundations, anchors and pipelines}, booktitle = {Cone {Penetration} {Testing} 2018: {Proceedings} of the 4th {International} {Symposium} on {Cone} {Penetration} {Testing} ({CPT}'18), {Delft}, {The} {Netherlands}, 21-22 {June} 2018}, publisher = {CRC Press}, author = {Randolph, M. F. and Stanier, S. A. and O'Loughlin, C. D. and Chow, S. and Bienen, B. and Doherty, J. P. and Mohr, H. and Ragni, R. and Schneider, M. A. and White, D. J. and Schneider, J.}, year = {2018}, keywords = {shallow penetrometer, offshore site investgation}, pages = {3--23} } - Ragni, R., Bienen, B., Stanier, S. A., Cassidy, M. J., & O’Loughlin, C. D. (2018). Visualisation of mechanisms governing suction bucket installation in dense sand. Proceedings of the 9th International Conference on Physical Modelling in Geotechnics (ICPMG 2018), July 17-20, 2018, London, United Kingdom, 651–656.Suction buckets are an increasingly considered foundation option for offshore wind turbines. Although the required suction can be predicted well using existing methods, uncertainty remains around some input parameters, because the effects of suction installation on the soil state are not understood in detail. This paper visualises the mechanisms governing both initial self-weight penetration and following suction-assisted installation in dense sand. Pioneering particle image velocimetry measurements in a centrifuge environment underpinned the investigation, with details of the experimental apparatus offered in the paper. Changes in the deformation mechanisms governing the installation process and in the soil properties are revealed. The findings have an impact on the understanding of the formation of internal plug heave – the cause of premature refusal – and the prediction of the installation response. Revealing changes in void ratio and permeability also present implications on the accumulated displacements under the metocean loading, which may conflict with serviceability requirements.
@inproceedings{ragni_visualisation_2018, title = {Visualisation of mechanisms governing suction bucket installation in dense sand}, booktitle = {Proceedings of the 9th {International} {Conference} on {Physical} {Modelling} in {Geotechnics} ({ICPMG} 2018), {July} 17-20, 2018, {London}, {United} {Kingdom}}, publisher = {Taylor \& Francis}, author = {Ragni, R. and Bienen, B. and Stanier, S. A. and Cassidy, M. J. and O'Loughlin, C. D.}, year = {2018}, keywords = {DIC, PIV, suction, caisson}, pages = {651--656} } - White, D. J., Stanier, S. A., Schneider, M. A., O’Loughlin, C. D., Chow, S. H., Randolph, M. F., Draper, S. D., Mohr, H., Morton, J. P., Peuchen, J., Fearon, R., Roux, A., & Chow, F. C. (2017). Remote Intelligent Geotechnical Seabed Surveys: technology emerging from the RIGSS JIP. Offshore Site Investigation Geotechnics 8th International Conference Proceeding, 1214–1222. https://doi.org/info:doi/10.3723/OSIG17.1214The Remote Intelligent Geotechnical Seabed Surveys (RIGSS) Joint Industry Project (JIP) is advancing geo-technical site investigation technology. The JIP is developing new types of tools with improved control and instrumentation, and new analysis methods to allow more direct application of data to geotechnical design. The JIP is motivated by three visions: (i) improved use of robotics and intelligent sensors to characterise the seabed, (ii) technologies that are simpler and cheaper to apply early in the project cycle, giving early infor-mation, and (iii) a trend towards ‘direct design’ from in situ test results, meaning that measurements can be scaled more directly to geotechnical design applications. Examples of improved site investigation technolo-gies are highlighted. An example of ball penetrometer analysis is described, including dissipation solutions that show the ball can provide more rapid determination of consolidation coefficient than a standard cone penetrometer. A recent class of shallow penetrometer devices is described, which are rotated as well as pushed vertically, allowing a greater range of soil properties to be derived for the geotechnical design of pipelines. Fi-nally, new hardware and interpretations for free fall penetrometers are shown. These advances improve the tools and interpretation methods available for seabed surveys. The sponsors of the JIP are Fugro, Shell, Total and Woodside Energy.
@inproceedings{white_remote_2017, title = {Remote {Intelligent} {Geotechnical} {Seabed} {Surveys}: technology emerging from the {RIGSS} {JIP}}, booktitle = {Offshore {Site} {Investigation} {Geotechnics} 8th {International} {Conference} {Proceeding}}, publisher = {Society of Underwater Technology}, author = {White, D. J. and Stanier, S. A. and Schneider, M. A. and O’Loughlin, C. D. and Chow, S. H. and Randolph, M. F. and Draper, S. D. and Mohr, H. and Morton, J. P. and Peuchen, J. and Fearon, R. and Roux, A. and Chow, F. C.}, month = jan, year = {2017}, doi = {info:doi/10.3723/OSIG17.1214}, keywords = {shallow penetrometer, RIGSS JIP, offshore site investigation}, pages = {1214--1222} } - O’Loughlin, C. D., White, D. J., & Stanier, S. A. (2017). Plate anchors for mooring floating facilities: a view towards unlocking cost and risk benefits. Offshore Site Investigation Geotechnics 8th International Conference Proceeding, 978–986. https://doi.org/info:doi/10.3723/OSIG17.978Optimisation of anchoring technology through improved design or through novel anchor types offers potential cost benefits and risk reduction. This paper makes the case for follower-embedded plate anchors and examines opportunities for refining their current design basis as articulated in design codes to reduce cost and risk. We recast the expression for anchor capacity by separating out uncertainties due to (i) bearing capacity factor, (ii) final embedment depth and (iii) soil strength. This permits sources of uncertainty to be more clearly identified, yielding better strategies for their reduction. Examples described include dynamically embedded plate anchors that self-correct for strength uncertainty, and consolidation-induced increases in the soil strength around the anchor and its connecting mooring chain. Research activities aligned with these opportunities are set out.
@inproceedings{oloughlin_plate_2017, title = {Plate anchors for mooring floating facilities: a view towards unlocking cost and risk benefits}, booktitle = {Offshore {Site} {Investigation} {Geotechnics} 8th {International} {Conference} {Proceeding}}, author = {O’Loughlin, C. D. and White, D. J. and Stanier, S. A.}, month = jan, year = {2017}, doi = {info:doi/10.3723/OSIG17.978}, keywords = {anchors, moorings}, pages = {978--986} } - Gourvenec, S. M., Stanier, S. A., White, D. J., Morgan, N., Banimahd, M., & Chen, J. (2017). Whole-life assessment of subsea shallow foundation capacity. Offshore Site Investigation Geotechnics 8th International Conference Proceeding, 787–795. https://doi.org/info:doi/10.3723/OSIG17.787Geotechnical design of subsea shallow foundations is typically based on in situ seabed strength reduced to take account of cyclic load degradation, in conjunction with the peak design load. This design philosophy emerged for fixed structures, designed to survive storms. However, subsea shallow foundation loading sequences and the associated seabed response differ significantly from that for fixed structures. They have periods that are orders of magnitude longer than storm loading, allowing for excess pore pressure dissipation during or between loading cycles that can lead to cyclic hardening rather than cyclic degradation of the supporting seabed. In addition, an alternative philosophy of tolerable mobility allows design loads that result from expansions or misalignments to be relieved if the foundation can displace and the soil-structure interaction be quantified. Greater scrutiny of the whole-life loading, soil-structure interaction and the associated seabed response can lead to efficiencies in foundation footprint, easing installability and reducing cost. This paper describes this ‘staircase’ of improvements in subsea shallow foundation design philosophy that are being explored in the ARC Research Hub for Offshore Floating Facilities, and provides examples to support the ideas presented.
@inproceedings{gourvenec_whole-life_2017, title = {Whole-life assessment of subsea shallow foundation capacity}, booktitle = {Offshore {Site} {Investigation} {Geotechnics} 8th {International} {Conference} {Proceeding}}, author = {Gourvenec, S. M. and Stanier, S. A. and White, D. J. and Morgan, N. and Banimahd, M. and Chen, J.}, month = jan, year = {2017}, doi = {info:doi/10.3723/OSIG17.787}, keywords = {whole-life, shallow foundations}, pages = {787--795} } - Teng, Y., Stanier, S. A., & Gourvenec, S. (2017). Analysis of failure mechanisms in silica and carbonate sands beneath a strip foundation under vertical loading. V009T10A016–V009T10A016. https://doi.org/10.1115/OMAE2017-61130This paper reports the deformation behavior of silica and carbonate sands under a strip foundation subjected to uniaxial vertical load. Small-scale physical modelling tests of a strip surface foundation under vertical load were conducted in a geotechnical centrifuge and Particle Image Velocimetry/Digital Image Correlation (PIV/DIC) was used to analyze images of an exposed plane of the model beneath the foundation to visualize the failure mechanisms. The observed mechanisms are interpreted in conjunction with load-settlement response and cone penetrometer resistance profiles. The failure mechanisms are illustrated through normalized vertical and horizontal displacement fields and shear and volumetric strain fields derived from the PIV analysis. Different soil deformation mechanisms and load-settlement responses were observed in the different sands. Soil resistance profiles measured using a miniature cone penetrometer do not correlate with the measured foundation bearing resistance and an interpretation of particle shape effect is introduced to explain the differing behaviors. The results presented improve understanding of the different responses in carbonate sands and silica sand beneath a shallow foundation under vertical load.
@inproceedings{teng_analysis_2017, title = {Analysis of failure mechanisms in silica and carbonate sands beneath a strip foundation under vertical loading}, doi = {10.1115/OMAE2017-61130}, publisher = {American Society of Mechanical Engineers}, author = {Teng, Yining and Stanier, S. A. and Gourvenec, Susan}, month = jun, year = {2017}, pages = {V009T10A016--V009T10A016} } - O’Loughlin, C. D., White, D. J., & Stanier, S. A. (2015, May). Novel anchoring solutions for FLNG - opportunities driven by scale. https://doi.org/10.4043/26032-MSFLNG facilities present a more onerous anchoring requirement than existing floating structures. Optimisation of the anchoring technology through improved design or through novel anchor types offers potential cost and risk benefits. These benefits may also be applicable to smaller moorings for MODUs and FPSOs. This paper uses concept–level design calculations of anchor capacity to compare different anchor technologies in the context of FLNG and MODU/FPSO applications. Also, new observations fromphysical modelling of chain–soil interaction are presented. Opportunities are identified for significant cost and schedule savings by adopting the alternative plate anchor technologies that are either suction or dynamically installed. Considering fabrication alone, the estimated costs are reduced by 70% for FLNG and 80% for MODUs relative to the conventional suction caisson option. When installation vessel costs are considered, the absolute cost saving could be far higher than from fabrication alone because installation could be from an anchor– handling vessel rather than a construction barge with a heavy lift crane. Torpedo anchors have also been considered, but are less attractive. Centrifuge model data and calculations of the shape and capacity of the embedded anchor chain suggest that there may be over–looked capacity from the mooring chain both on and within the seabed. At the same time, upscaling of embedded plates to the scale required for FLNG applications increases the amount of chain slack that would be released into the mooring during in service loading, and this effect requires consideration in the overall mooring system design. Research and development activities aligned with the opportunities for reduced cost and risk in anchoring design are set out.
@inproceedings{oloughlin_novel_2015, title = {Novel anchoring solutions for {FLNG} - opportunities driven by scale}, doi = {10.4043/26032-MS}, publisher = {Offshore Technology Conference}, author = {O'Loughlin, C. D. and White, D. J. and Stanier, S. A.}, month = may, year = {2015}, keywords = {FLNG, anchors, moorings} } - Todeshkejoei, C., Hambleton, J. P., Stanier, S. A., & Gaudin, C. (2015). Modelling installation of helical anchors in clay. Computer Methods and Recent Advances in Geomechanics - Proc. of the 14th International Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014, 917–922.Helical anchors, which are mostly used to resist uplift, are deep foundations installed by rotation into the ground. Despite the central role of the installation process, especially with respect to the effect of soil disturbance, relatively little is known about the forces and deformations occurring during installation. An exception is the field verification technique known as torque-capacity correlation, which attempts to relate installation torque directly to uplift capacity. However, there are open questions regarding this approach, since not all significant parameters, such as installation vertical force and helix pitch, are taken into consideration. This could be one of the main reasons behind the wide range of torque-correlation factors reported in the literature. This study presents a three-dimensional numerical analysis of the installation process for helical anchors in clay. The results are synthesised into convenient yield envelopes that predict the relationship between installation torque and normal force as functions of helix pitch, roughness, and thickness. The application of the findings to torque-capacity correlation is also discussed.
@inproceedings{todeshkejoei_modelling_2015, title = {Modelling installation of helical anchors in clay}, booktitle = {Computer {Methods} and {Recent} {Advances} in {Geomechanics} - {Proc}. of the 14th {International} {Conference} of {International} {Association} for {Computer} {Methods} and {Recent} {Advances} in {Geomechanics}, {IACMAG} 2014}, publisher = {Taylor \& Francis}, author = {Todeshkejoei, C. and Hambleton, J. P. and Stanier, S. A. and Gaudin, C.}, year = {2015}, keywords = {clay, helical piles}, pages = {917--922} } - Kashizadeh, E., Hambleton, J. P., & Stanier, S. A. (2015). A numerical approach for modelling the ploughing process in sands. Computer Methods and Recent Advances in Geomechanics - Proc. of the 14th International Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014, 159–164.Ploughing processes are difficult to simulate using conventional approaches due to the occurrence of extremely large, predominantly plastic deformation. Numerical techniques such as the Material Point Method and the Discrete Element Method are, in principle, capable of reproducing the deformation observed in these evolutionary processes, but they are not without drawbacks, the most significant being the large processing times required. This paper presents a new numerical technique for modeling the ploughing process in sands. The method rests on the assumption that deformation occurs in the form of strong discontinuities, or shear bands, and considers the full process as a sequence of incipient collapse problems. Within an increment of deformation, the collapse mechanism furnishing the least resistance is used to update the deformed configuration and evaluate force. The model incorporates the effect of softening within the shear bands, as well as material avalanching observed as the slope of the free surface reaches the critical angle at which instabilities occur. Theoretical predictions are compared to experiments, and the basic similarities and difference are discussed.
@inproceedings{kashizadeh_numerical_2015, title = {A numerical approach for modelling the ploughing process in sands}, booktitle = {Computer {Methods} and {Recent} {Advances} in {Geomechanics} - {Proc}. of the 14th {International} {Conference} of {International} {Association} for {Computer} {Methods} and {Recent} {Advances} in {Geomechanics}, {IACMAG} 2014}, publisher = {Taylor \& Francis}, author = {Kashizadeh, E. and Hambleton, J. P. and Stanier, S. A.}, year = {2015}, keywords = {sand, ploughing}, pages = {159--164} } - Ullah, S. N., Hu, Y., White, D. J., & Stanier, S. A. (2014). Lateral boundary effect in centrifuge tests for spudcan penetration in uniform clay. Applied Mechanics and Materials. https://doi.org/10.4028/www.scientific.net/AMM.553.458The effect of the centrifuge strongbox boundary on the penetration resistance of a spudcan foundation in uniform clay has been studied using Large Deformation FE analysis. Both smooth and rough strongbox boundaries were considered with various strongbox sizes. The spudcan penetration resistance and soil flow mechanisms were analysed. It was observed that, when the strongbox size was reduced, the spudcan penetration resistance was decreased for a smooth boundary and increased for a rough boundary. The depth of cavity formed above the spudcan during its penetration, in most cases, was determined by the soil flow around mechanism without cavity wall failure. However, cavity wall failure could be initiated when a smooth strongbox boundary was very close to the spudcan. The strongbox boundary effect on the spudcan penetration resistance can be avoided when the distance of the strongbox boundary to the spudcan centre is larger than 1.5 times of spudcan diameter for a rough boundary; or 2 times of spudcan diameter for a smooth boundary.
@inproceedings{ullah_lateral_2014, title = {Lateral boundary effect in centrifuge tests for spudcan penetration in uniform clay}, booktitle = {Applied {Mechanics} and {Materials}}, author = {Ullah, S. N. and Hu, Y. and White, D. J. and Stanier, S. A.}, year = {2014}, doi = {10.4028/www.scientific.net/AMM.553.458}, keywords = {centrifuge modelling, spudcan, boundary effects, LDFE} } - Ullah, S. N., Stanier, S. A., White, D. J., & Hu, Y. (2014). Using the ‘step zero’ approach to design a centrifuge modelling program. Physical Modelling in Geotechnics: Proceedings of the 8th International Conference on Physical Modelling in Geotechnics 2014, ICPMG 2014, 1, 397–403.The design of a centrifuge modeling program for a clay bed with an interbedded sand layer is outlined following the ‘step zero’ approach. A modified sand overlying clay model was used incorporating the top clay as an effective surcharge. The tests aimed to investigate punch through failure, and the subsequent stabilization of bearing capacity. To this behavior within the limited depth of the test box a certain vertical free boundary distance (F _BD) is required, which controls the required ratio of soil sample depth to foundation size. In assessing this requirement based on existing calculation methods for punch through, the following four factors were found to be crucial: (i) intercept strength of clay at sand-clay interface; (ii) soil strength gradient of the clay layer; (iii) relative density of sand; and (iv) relative sand layer thickness to foundation diameter. As a result of planning and implementing a ‘step zero’ approach, the majority of the tests successfully captured the peak resistance and the depth of the punch-through event. The planning approach demonstrated here serves as an example for future centrifuge test design in similar scenarios.
@inproceedings{ullah_using_2014, title = {Using the `step zero' approach to design a centrifuge modelling program}, volume = {1}, booktitle = {Physical {Modelling} in {Geotechnics}: {Proceedings} of the 8th {International} {Conference} on {Physical} {Modelling} in {Geotechnics} 2014, {ICPMG} 2014}, publisher = {CRC Press}, author = {Ullah, S. N. and Stanier, S. A. and White, D. J. and Hu, Y.}, collaborator = {Ullah, S. N. and Stanier, S. A. and White, D. J. and Hu, Y.}, year = {2014}, keywords = {centrifuge modelling, step zero}, pages = {397--403} } - Stanier, S. A., Hu, P., & Cassidy, M. J. (2012). Calibration of a model to predict the peak punch-through penetration resistance of a spudcan on sand overlying clay. 2nd European Conference on Physical Modelling in Geotechnics.This paper demonstrates the use of a geotechnical drum centrifuge in the calibration of a model to predict the peak punch-through penetration (qpeak) resistance of a spudcan on sand overlying clay. A series of loose sand overlying clay tests was performed and combined with an existing database of tests performed on dense sand overlying clay. The performance of the failure stress dependent model proposed by Lee (2009) and Lee et al. (2009) has then been assessed using this combined dataset which encompasses a wider range of soil properties and problem geometries than was used in the original calibration of the model. The single empirical stress distribution factor (DF) that is employed in the model was then optimised using a back calculation procedure for all tests. The scatter of the optimised DF values was then compared for the original bi-linear calibration proposed by Lee et al. (2009) and a new nonlinear power law calibration. The new non-linear relationship enables the model to better predict qpeak over a wider range of problem geometries and for conditions of both loose and dense sands overlying clay. The work demonstrates the importance of the geotechnical centrifuge in calibrating such models given that at present numerical methods are unable to reliably capture such punch-through behaviour and good quality field data of punch-through failure of spudcan foundations is unavailable
@inproceedings{stanier_calibration_2012, title = {Calibration of a model to predict the peak punch-through penetration resistance of a spudcan on sand overlying clay}, language = {en}, booktitle = {2nd {European} {Conference} on {Physical} {Modelling} in {Geotechnics}}, publisher = {Delft University of Technology and Deltares}, author = {Stanier, S. A. and Hu, P. and Cassidy, M. J.}, year = {2012}, keywords = {punch-through, spudcan} } - Hird, C. C., & Stanier, S. A. (2010). Modelling helical screw piles in clay using a transparent soil. Physical Modelling in Geotechnics - Proceedings of the 7th International Conference on Physical Modelling in Geotechnics 2010, ICPMG 2010, 2, 769–774.A transparent synthetic soil consisting of fumed silica particles and a pore fluid with matched refractive index has been used to represent clay in a physical model of the installation and undrained load-deflection performance of helical screw piles in a deep installation condition. A digital camera captures images during installation and load-deflection testing, allowing the use of Particle Image Velocimetry (PIV) techniques to compute displacement fields around the piles. This experimental method is being used to assess the effect of the helical plate spacing ratio on the failure mode and load deflection performance of single and multi-helical plate screw piles loaded in tension and compression, at a constant strain rate. Initial results are presented indicating significantly differing behaviour with respect to the configuration of the helical screw pile. The precision of the PIV output is significantly better than in previous analyses conducted using transparent soils in similar non-intrusive modelling scenarios. © 2010 Taylor & Francis Group, London.
@inproceedings{hird_modelling_2010, title = {Modelling helical screw piles in clay using a transparent soil}, volume = {2}, booktitle = {Physical {Modelling} in {Geotechnics} - {Proceedings} of the 7th {International} {Conference} on {Physical} {Modelling} in {Geotechnics} 2010, {ICPMG} 2010}, author = {Hird, C. C. and Stanier, S. A.}, month = dec, year = {2010}, keywords = {transparent soil, helical piles}, pages = {769--774} } - Stanier, S. A., & Tarantino, A. (2010). Active earth force in ‘cohesionless’ unsaturated soils using bound theorems of plasticity. Unsaturated Soils - Proceedings of the 5th International Conference on Unsaturated Soils, 2, 1081–1086.Granular ‘cohesionless’ soils above the water table are partially saturated but are commonly assumed to be dry in geotechnical practice. The ‘dry soil’ assumption neglects the effect of suction on shear strength and soil structures are therefore over-designed. This paper presents an approach to the analysis of collapse of soil structures above the water table based on the upper and lower bound theorems of plasticity. As an example, the active earth force on a retaining wall has been calculated and compared to the value obtained from the classical ‘dry’ approach.
@inproceedings{stanier_active_2010, title = {Active earth force in `cohesionless' unsaturated soils using bound theorems of plasticity}, volume = {2}, booktitle = {Unsaturated {Soils} - {Proceedings} of the 5th {International} {Conference} on {Unsaturated} {Soils}}, author = {Stanier, S. A. and Tarantino, A.}, keywords = {excavation, limit analysis, partial saturation, unsaturated}, year = {2010}, pages = {1081--1086} } - Black, J. A., Stanier, S. A., & Clarke, S. D. (2009). Shear wave velocity measurement of kaolin during undrained unconsolidated triaxial compression. Proceedings of the 62nd Canadian Geotechnical Conference.Undrained shear strength of cohesive soils is traditionally evaluated in the laboratory through the use of undrained unconsolidated triaxial compression tests. More recently the measurement of shear wave velocity using bender elements has become increasingly popular for the assessment of soil properties due to its simplicity. In the present research shear wave velocity is used to examine the undrained shear strength of 100mm diameter kaolin clay specimens manufactured by compaction at various moisture contents. The results indicate a correlation between undrained shear strength and shear wave velocity which is responsive to axial strain, which is likely a phenomena caused by the sample generation process utilised in the presented preliminary results.
@inproceedings{black_shear_2009, title = {Shear wave velocity measurement of kaolin during undrained unconsolidated triaxial compression}, copyright = {All rights reserved}, booktitle = {Proceedings of the 62nd {Canadian} {Geotechnical} {Conference}}, author = {Black, J. A. and Stanier, S. A. and Clarke, S. D.}, year = {2009}, keywords = {shear wave velocity, triaxial, kaolin} }
Theses
- Stanier, S. A. (2011). Modelling the behaviour of helical screw piles [PhD thesis]. University of Sheffield.The research described in this thesis concerns modelling the behaviour of helical screw piles using both physical and numerical modelling techniques. A review of published literature highlighted that the influence of the geometry of helical screw piles on their performance and failure mechanisms is not definitively known. Development of transparent synthetic soils has facilitated observation of soil displacements around helical screw piles during both installation and load testing using small scale 1g physical models. This allowed the failure mechanisms to be identified for helical screw piles of varying geometry and comparison to be drawn with parallel numerical simulations. The transparent soil utilised was representative of soft clay and allowed non-intrusive measurement of displacements on a plane highlighted by a sheet of laser light allowing a digital camera to record movement of the soil. This enabled Particle Image Velocimetry to be used to measure the displacement of the soil on the target plane. This allowed observation of both the installation induced disturbance and the displacement and shear strain fields mobilised around deeply installed helical screw piles with 20mm diameter helical plates on a 5mm diameter shaft, under compressive and tensile loading. The results of the physical model tests demonstrated that the geometry of helical screw piles significantly impacted on their behaviour in soft clay soils. The installation disturbance induced by helical screw pile installation was shown to be related to the volume of the pile and that most disturbance was caused by the installation of the lowermost helical plate. Additional helical plates following the installation path of the lowermost plate caused less disturbance. Under loading the spacing of the helical plates was shown to control the stiffness of the piles’ load-deflection response and the distance between the uppermost and lowermost helical plates, was shown to govern the ultimate capacity. The compressive and tensile capacities of deeply installed helical screw piles were demonstrated to be very similar. The geotechnical properties of the transparent soil beds tested were assessed by per forming in-situ hand vane shear tests and Undrained Unconsolidated (UU) triaxial tests on extracted specimens. A novel method of assessing the non-linear stress-strain characteristics of the transparent soil based upon the Mobilisable Strength Design (MSD) method of Osman & Bolton (2005) was then investigated using the same non-intrusive modelling techniques as for the helical screw piles. From this collection of property data a simple elasto-plastic constitutive model was calibrated that described the stress-strain response of the transparent soil used in the physical models. This allowed comparative Finite Element (FE) simulations of the model footing tests to be created. In general the agreement between the physical model and FE model was good. However, the deformation mechanism assumed by Osman & Bolton (2005) was somewhat different to that observed in the physical model tests or numerical simulations. FE simulations of the helical screw pile tests were also performed with the helical plate geometry simplified as flat circular plates and the piles were ‘wished’ into place. Hence, installation induced effects were not reproduced in the FE simulations. Comparisons of the displacement and shear strain fields between the physical models and numerical simulations were generally good for both compressive and tensile loading. However, comparison of the load-deflection responses indicated that the FE simulations underpredicted the initial stiffness of the load-deflection responses for all helical screw piles. The general trends related to the effect of the geometry of the helical screw piles observed in the physical models were preserved in the FE simulations. Lastly, a simple analytical model was shown to provide adequate prediction of ultimate capacity for helical screw piles loaded in compression or tension. Design methodologies including Eurocode 7, the traditional permissible stress approach and a method based upon reserving base or uplift capacity were then used to calculate design capacities. This highlighted the importance of minimising the spacing between the helical plates to optimise performance and the importance of separate serviceability limit state checks if maximum economy is sought in design.
@phdthesis{stanier_modelling_2011, title = {Modelling the behaviour of helical screw piles}, school = {University of Sheffield}, author = {Stanier, S. A.}, month = may, year = {2011}, keywords = {transparent soil, helical piles} }