Three simplified models for the analytic determination of the dynamic response of a crossanisotropic poroelastic half-plane to a load moving with constant speed on its surface are presented and compared against the corresponding exact model. The method of analysis of the exact and approximate models uses complex Fourier series to expand the load and the displacement responses along the horizontal direction of the steady-state motion and thus reduces the partial differential equations of the problem to ordinary ones, which are easily solved. The three simplified models are characterized by reasonable simplifying assumptions, which reduce the complexity of the exact model and facilitate the solution. In the first simplified model all the terms of the equations of motion associated with fluid acceleration are neglected. In the second simplified model, solid displacements are assumed to be equal to the corresponding fluid ones, while the third simplified model is the second one corrected with respect to the fluid pressure at the free boundary (top) layer. All three simplified models are compared with respect to their accuracy against the exact model and the appropriate range of values of the various significant parameters of the problem, like porosity, permeability, anisotropy indices, or load speed, for obtaining approximate solutions as close to the exact solution as possible is thoroughly discussed.

This work proposes a novel plastic damage model to capture the post elastic flow-controlled damages in pavement-soil systems prescribed by the vibrations of moving load. Initially, the pavement structure has been modelled as a single-layer system resting on a spring-dashpot system representing soil mass. Then, multilayer modelling was adopted to analyze the post-elastic dynamic response in supporting plastic flow-controlled layers of geomaterial. Three mechanistic zones namely, elastic recoverable, transition, and post elastic zone have been conceptualized to identify the damage. The nonlinearity in stress and equivalent plastic strain has been observed for the set of selected velocities and load intensities specified in codal provisions. The variation in equivalent plastic strain is observed in the range of 10-16 to 10-3% in the granular base layer and 10-16 to 10-4% in the subgrade soil layer. The findings show that the equivalent plastic strain due to plastic flow prescribed by the vibrations of moving action of vehicular load at varied velocities is one of the root causes of permanent deformations. The propagation of dynamic load vibrations from the uppermost layer of pavement induces the generation of stress waves within distinct sub-layers of geomaterial. Hence, the observed behaviour leads to the generation of nonlinear stress waves prescribed by a vibrational mechanism of stress transfer (VMST). Therefore, the evaluation of the nonlinearities causing damage in pavement structure supported by flow controlled geomaterials has the potential to predict permanent deformations and its implications in the design of pavements supporting the transportation network.

Transport systems such as highways and railways are constructed on earthworks that experience fluctuating levels of saturation. This can range from dry to fully saturated, however most commonly they are in a state of partial saturation. When numerically modelling such problems, it is important to capture the response of the solid, liquid and gas phases in the material. However, multi-physics solutions are computationally demanding and as a solution this paper presents a finite element approach for the dynamic analysis of unsaturated porous media in a moving coordinate system. The first novelty of the work is the development of a principle of relative motion for a three-phase medium, where the moving load is at rest while the unsaturated porous medium moves relative to the load. This makes it particularly efficient for moving load problems such as transport. The second novelty is a parametric investigation of the three-phase response of a partially saturated medium subject to a moving load. The paper starts by presenting the time domain model in terms of its constitutive relationships and equations for mass and momentum conservation. Next the model is validated using three case studies: the consolidation of a saturated soil column, the dynamics of an unsaturated soil column and finally the response of a saturated foundation to a moving load. It is then used to study a moving 2D plane strain load problem and its performance is compared to that of a standard FEM solution which does not employ a moving coordinate system. Similar accuracy is obtained while computational efficiency is improved by a factor of ten. Finally, the model is used to investigate the effect of degree of saturation and moving load speed on the response of an unsaturated porous medium. It is found that both variables have a significant impact on the dynamic response.