Abstract:
This thesis seeks to shed more light on the dynamic behaviour and failure mechanisms of gravity cantilevered and mechanically stabilised earth (MSE) wall systems when retaining compacted cohesionless soil. OpenSees, an open-source finite element software system, is utilised to simulate soil-structure interaction in a 2D environment under static and earthquake loading. Recent advances in constitutive models have propelled us to understand soil behaviour better. Hence, Manzari & Dafalias (MD) employed a two-surface plasticity model with a non-associative flow rule to model dry sand. The MD material can represent the full range of pressure-dependent shear deformation and volume change behaviour of cohesionless soil with one set of material parameters and specify the initial state of a particular soil through the void ratio and confining stress. Although sliding might be the primary failure mechanism of a gravity cantilevered retaining wall founded on very stiff soil or rock, rotation of the wall might be more significant in most cases. Rotational deformation at the foundation level would translate into rotational deformation of the wall, which might involve rotational bearing failure of the foundation.
To this date, the design of retention systems is based on the pseudo-static approach chiefly, assuming the wall maximum active thrust is continuously present. In contrast, this thrust is mobilised only for a short period during a seismic event. Nonlinear time-history analyses have been implemented to assess the behaviour of gravity cantilevered retaining wall systems. As an alternative option, MSE walls are used due to their sustainability, robustness and simplicity of construction. The reinforcement component of an MSE wall is believed to enforce a rigid behaviour in the reinforced soil area. This idea has been tested by assessing the dynamic response of MSE walls with varying lateral extent for reinforcement layers. The MSE wall systems have been compared with a block of elastic orthotropic material having a horizontal elastic modulus larger than its value in the vertical direction. It is shown that the global responses of these two systems are reasonably comparable. Finally, it is shown that both well-designed gravity cantilevered retaining and MSE walls show satisfactory behaviour under medium intensity earthquakes, with MSE walls exhibiting less maximum and post-seismic deformations. Although the MSE wall behaves similar to a rigid body, the soil body above the gravity cantilevered retaining wall might not move with the wall structure despite the theory.