Sam Stanier

Predicting peak resistance of spudcan penetrating sand overlying clay

AbstractAccurately 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 b...

Improved Image-Based Deformation Measurement in the Centrifuge Environment

This 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 methods 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 punch-through 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.

Effects of Consolidation under a Penetrating Footing in Carbonate Silty Clay

AbstractThe 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-pene...

Novel Anchoring Solutions for FLNG - Opportunities Driven by Scale

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Lateral boundary effect in centrifuge tests for spudcan penetration in uniform clay

The 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.

Predicting wheel forces using bearing capacity theory for general planar loads

This 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.