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This thesis describes a numerical investigation of shallow circular foundations resting on various types of soil, mainly siliceous and calcareous sands. An elasto-plastic constitutive model, namely the MIT-S1 model (Pestana, 1994), which can predict the rate independent behaviour of different types of soils ranging through uncemented sands, silts and clays, is used to simulating the compression, drained triaxial shear and shallow circular foundation responses. It is found that this model provides a reasonable fit to measured behaviour, particularly for highly compressible calcareous sands, because of the superior modelling of the volumetric compression. The features of the MIT-S1 model have been used to investigate the effects of density, stress level (or foundation size), inherent anisotropy and material type on the response of shallow foundations. It was found that the MIT-S1 model is able to distinguish responses on dilatant siliceous and compressible calcareous sands by relatively minor adjustment of the model parameters. Kinematic mechanisms extracted from finite element calculations show different deformation patterns typical for these sands, with a bulb of compressed material and punching shear for calcareous sand, and a classical rupture failure pattern accompanied by surface heave for siliceous sand. Moreover, it was observed that the classical failure pattern transforms gradually to a punching shear failure pattern as the foundation size increases. From this evidence, a dimensional transition between these failure mechanisms can be defined, referred to as the critical size. The critical size is also the limiting foundation size to apply conventional bearing capacity analyses. Alternative approaches are needed, focusing mainly on the soil compressibility, for shallow foundations greater than the critical size. Two approaches, 1-D compression and bearing modulus analyses, have been proposed for those foundation conditions. From the validations, the former is applicable for extremely large foundations, very loose soil conditions and highly compressible calcareous materials, while the latter is suitable for moderate levels of compressibility or foundation size. It is suggested that appropriate assessment of compression features is of great importance for shallow foundation analysis on sand.

Mobile offshore jack-up drilling rigs are not custom-designed for a particular location but rated for typical operating characteristics, like water depths. They may be deployed at a number of different sites during their design life. Under the current guidelines, the jack-up is required to be assessed for its suitability for each new proposed location, assuming environmental loading conditions due to wind, waves and current corresponding to a 50-year return period storm applicable to the site. Traditionally, these assessments have been performed in two dimensions, simplifying the jack-up to a plane frame and the loading conditions to be in-plane with the rig's 'axis of symmetry'. This thesis introduces a computer program, named SOS_3D, for the fluid-structure-soil interaction analysis of jack-up response in three dimensions. Extensive experimental series have been performed to provide evidence for the generalisation of the foundationsoil interaction model to general six degree-of-freedom loading conditions and its applicability to load paths and stress levels relevant to jack-up spudcans. These experiments included (1) 1g single footing tests, (2) centrifuge single footing tests and (3) centrifuge model jack-up tests. The latter tests highlighted differences in response and mode of failure depending on the loading direction of the jack-up and re-iterated the importance of three-dimensional modelling. The numerical program SOS_3D introduced early in this thesis was shown to represent a useful tool for the prediction of jack-up behaviour under general combined loading in three dimensions. It provided reasonably good, conservative predictions of the experimentally measured jack-up behaviour.

Indiana University-Purdue University Indianapolis (IUPUI) / In this thesis, an explicit time integration code which integrates multibody dynamics and the discrete element method is used for modelling the excavation and moving operation of cohesive soft soil (such as mud and snow) by bulldozers. A soft cohesive soil material model (that includes normal and tangential inter-particle force models) is used that can account for soil compressibility, plasticity, fracture, friction, viscosity and gain in cohesive strength due to compression. In addition, a time relaxation sub-model for the soil plastic deformation and cohesive strength is added in order to account for loss in soil cohesive strength and reduced bulk density due to tension or removal of the compression. This is essential in earth moving applications since the soil that is dug typically becomes loose soil that has lower shear strength and lower bulk density (larger volume) than compacted soil. If the model does not account for loss of soil shear strength then the dug soil pile in front of the blade of a bulldozer will have an artificially high shear strength. A penalty technique is used to impose joint and normal contact constraints. An asperity-based friction model is used to model contact and joint friction. A Cartesian Eulerian grid contact search algorithm is used to allow fast contact detection between particles. A recursive bounding box contact search algorithm is used to allow fast contact detection between the particles and polygonal contact surfaces. A multibody dynamics bulldozer model is created which includes the chassis/body, C-frame, blade, wheels and hydraulic actuators. The components are modelled as rigid bodies and are connected using revolute and prismatic joints. Rotary actuators along with PD (Proportional-Derivative) controllers are used to drive the wheels. Linear actuators along with PD controllers are used to drive the hydraulic actuators. Polygonal contact surfaces are defined for the tires and blade to model the interaction between the soil and the bulldozer. Simulations of a bulldozer performing typical shallow digging operations in a cohesive soil are presented. The simulation of a rear wheel drive bulldozer shows that, it has a limited digging capacity compared to the 4-wheel drive bulldozer. The effect of the relaxation parameter can be easily observed from the variation in the Bulldozer's velocity. The higher the relaxation parameter, the higher is the bulldozer's velocity while it is crossing over the soil patch. For the low penetration depth run the bulldozer takes less time compared to high penetration depth. Also higher magnitudes of torques at front and rear wheels can be observed in case of high penetration depth. The model is used to predict the wheel torque, wheel speed, vehicle speed and actuator forces during shallow digging operations on three types of soils and at two blade penetration depths. The model presented can be used to predict the motion, loads and required actuators forces and to improve the design of the various bulldozer components such as the blade, tires, engine and hydraulic actuators.