Research On Monotonic And Cyclic Behavior And Constitutive Model Of Three-dimensional Soil-Structure Interface

Based on the new experimental observations under three-dimensional loading conditions, a rational approach was explored systematically on the three-dimensional monotonic and cyclic behaviors of soil-structure interfaces from aspects of physical interpretations, constitutive model, and numerical implementation as well as practical application. The main achievements obtained in the thesis are as follows:1. A new, large-scale multifunction test apparatus was designed and developed to investigate the three-dimensional monotonic and cyclic behaviors of soil-structure interfaces. The maximum normal loading capacity is 800kN; and the maximum diameter of the circular sample is 500mm. Either direct shear or simple shear interface tests can be conducted using different soil containers. Various loading paths can be applied with an accurate three-dimensional loading device supported by a hydraulic servo system. Many tests on coarse-grained soil can also be conducted with the apparatus, including direct shear, simple shear and confined compression tests.2. Series of tests were systematically conducted on the interfaces between a steel plate and gravel under three-dimensional loading conditions. The monotonic and cyclic tests were performed under three kinds of loading paths, i.e., linear loading path, rotational loading path, and their combination. The tests, subjected to an application of displacements or loads, controlled in two perpendicular tangential directions, were conducted under different normal boundary conditions, including constant stress, constant displacement and constant stiffness. The effects of loading conditions were investigated carefully, including magnitude of loading, normal stress and normal stiffness.3. The fundamental rules of three-dimensional monotonic and cyclic behaviors of the interface have been studied on the basis of test results. The shear strength is insignificantly affected by the different loading paths. During the loading process, the physical states changed and governed the stress-strain response strongly. Strain-hardening occurs due to cyclic loading. Non-coaxial angle exists when the interface was subjected to a rotational loading. The volumetric strain due to dilatancy is composed of a reversible dilatancy component and an irreversible dilatancy one.4. A new three-dimensional cyclic constitutive model of the soil-structure interface was developed using the bounding surface and generalized plasticity theory based on the fundamental rules. The loading mechanism is rationally decomposed into linear and rotational loading, and a new method for evaluating the interface behavior related with the rotational loading was proposed. The present model is confirmed to capture the main features of the interface subjected to three-dimensional loading, from small strain to large strain.5. The finite element formulations of the present model was developed and implemented in a three-dimensional nonlinear FEM code. A concrete-faced rockfill dam was analyzed using the present constitutive model of the interface. The results confirmed the effectiveness of the model and the numerical implementation in the analysis of boundary-value problems involving soil-structure interfaces.