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Shallow foundations can provide the most economical solution for supporting small-scale structures. The design approach is quite simple considering the ultimate bearing capacity and working-load settlement. Research has shown that settlement calculations, determined using a linear-elastic approach, usually govern the design but this approach is inappropriate because soil is highly non-linear, even at small strains. The result is that signifi cant discrepancies are observed between predicted and actual settlements. This uncertainty has seen the development of settlement-based approaches such as Mobilisable Strength Design (MSD). MSD uses an assumed undrained mechanism and accounts for soil non-linearity by scaling a triaxial stress-strain curve to make direct predictions of footing load-settlement behaviour. Centrifuge experiments were conducted to investigate the mechanisms governing the settlement of shallow circular foundations on clay and saturated sand models. Clay model tests were performed on soft or rm kaolin beds, depending on its pre-consolidation. Sand model tests were performed on relatively loose Hostun sand saturated with methyl-cellulose to slow consolidation. One-dimensional actuators were developed to apply footing loads through dead-weight or pneumatic loading. A Perspex window in the centrifuge package allowed digital images to be captured of a central cross-section, during and after footing loading. These were used to deduce soil displacements by Particle Image Velocimetry which were consistent with footing settlements measured directly. Deformation mechanisms are presented for undrained penetration, consolidation due to transient flow, as measured by pore pressure transducers, and creep. A technique was developed for discriminating consolidation settlements from the varying rates of short and long-term creep of clay models. Using MSD, a method for predicting the undrained penetration of a spread foundation on clay was proposed, using database results alone, which then provided estimates of creep and consolidation settlements that follow. The importance of the undrained penetration necessitated further investigation by using the observed undrained mechanism as the basis of an ellipsoidal cavity expansion model. An upper-bound energy approach was used to determine the load-settlement behaviour of circular shallow foundations on linear-elastic and non-linear clays, with yield defined using the von Mises' yield criterion. Linear-elastic soil results were consistent with those obtained from nite element analyses. The non-linear model, as described by a power-law, showed good agreement with both centrifuge experiment results and some real case histories. The single design curve developed through this model for normalised footing pressure and settlement could be used by practising engineers based on existing soil correlations or site investigations.

abstract: The Atlantic razor clam burrows underground with effectiveness and efficiency by coordinating shape changings of its shell and foot. Inspired by the burrowing strategy of razor clams, this research is dedicated to developing a self-burrowing technology for active underground explorations by investigating the burrowing mechanism of razor clams from the perspective of soil mechanics. In this study, the razor clam was observed to burrow out of sands simply by extending and contracting its foot periodically. This upward burrowing gait is much simpler than its downward burrowing gait, which also involves opening/closing of the shell and dilation of the foot. The upward burrowing gait inspired the design of a self-burrowing-out soft robot, which drives itself out of sands naturally by extension and contraction through pneumatic inflation and deflation. A simplified analytical model was then proposed and explained the upward burrowing behavior of the robot and razor clams as the asymmetric nature of soil resistances applied on both ends due to the intrinsic stress gradient of sand deposits. To burrow downward, additional symmetry-breaking features are needed for the robot to increase the resistance in the upward burrowing direction and to decrease the resistance in the downward burrowing direction. A potential approach is by incorporating friction anisotropy, which was then experimentally demonstrated to affect the upward burrowing of the soft robot. The downward burrowing gait of razor clams provides another inspiration. By exploring the analogies between the downward burrowing gait and in-situ soil characterization methods, a clam-inspired shape-changing penetrator was designed and penetrated dry granular materials both numerically and experimentally. Results demonstrated that the shell opening not only contributes to forming a penetration anchor by compressing the surrounding particles, but also reduces the foot penetration resistance temporally by creating a stress arch above the foot; the shell closing facilitates the downward burrowing by reducing the friction resistance to the subsequent shell retraction. Findings from this research shed lights on the future design of a clam-inspired self-burrowing robot. / Dissertation/Thesis / Video for section A1 of APPENDIX A / Video for section A2 of APPENDIX A / Video for section A3 of APPENDIX A / Video for section B8 of APPENDIX B / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2020

For more than five decades, hydraulic fracturing has been widely used to enhance oil and gas production. Hydraulic fracturing in solid materials (e.g., rock) has been studied extensively. The main goal of this thesis is a comprehensive study of the physical mechanisms of hydraulic fracturing in cohesionless sediments. For this purpose, experimental techniques are developed to quantify the initiation and propagation of hydraulic fractures in dry particulate materials. We have conducted a comprehensive experimental series by varying such controlling parameters as the properties of particulate materials and fracturing fluids, boundary conditions, initial stress states, and injection volumes and rates. In this work, we suggest principle fundamental mechanisms of hydraulic fracturing in particulate materials and determine relevant scaling relationships (e.g., the interplay between elastic and plastic processes). The main conclusion of this work is that hydraulic fracturing in particulate materials is not only possible, but even probable if the fluid leak-off is minimized (e.g., high flow rate, high viscosity, low permeability). Another important conclusion of this work is that all parts of the particulate material are likely to be in compression. Also, the scale effect (within the range of the laboratory scales) appears to be relatively insignificant, that is, the observed features of fractures of different sizes are similar. Based on the observed fracture geometries, and injection pressures we suggested three models of hydraulic fracturing in particulate materials. In the cavity expansion or ??e driving model, the fracturing fluid is viewed as a sheet pile (blade) that disjoints the host material, and the cavity expansion occurs at the fracture (blade) front. The shear banding model is also consistent with a compressive stress state everywhere in the particulate material and explains the commonly observed beveled fracture front. The model of induced cohesion is based on the fluid leak-off ahead of the fracture front. The induced cohesion may be caused by the tensile strain near the fracture tip (where the stress state is also compressive), which, in turn, induces the cavitation of the leaked-off fluid and hence capillary forces.