Modeling of pore pressure propagation and dissipation in compressible porous media

Hachem, Hussein A.
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This research is a study of the different phenomena associated with the propagation of pore water pressure in high plasticity clays. Specifically, it addresses the pore pressure response in areas subjected to sudden increases in pore water pressure at their top boundary. The main applications of this research would be the study of pore pressure responses in grouted piezometers and the pore pressure buildup in areas with rainfall-induced landslides failures. This phenomenon of pore pressure diffusion is coupled with Terzaghi’s theory of consolidation. For that purpose, an analysis of pulse tests (consisting of measuring pore pressure response with time due to increases in pore water pressure boundary conditions) conducted by previous researchers is performed. In conjunction with the pulse tests, modified consolidation tests are also executed. The coefficients of diffusion affecting the pore pressure response in each of these cases are then evaluated. In addition, an analytical model is developed to mathematically describe the pore pressure response in clays under pressure pulses. The derivation of the differential equation describing this response makes use of Darcy’s theory of flow in porous media, where a difference in gradients causes a difference in flow patterns. The derived equation is then compared to Terzaghi’s equation of consolidation. This couples model shows that a sudden pulse of pressure causes a slower pore pressure response than the one caused by an increase of total stress. The role that pore pressure diffusion and consolidation simultaneously contribute are studied in a modified CRS consolidation setup. The mathematical modeling of these processes together is compared to the experimental results. Due to these two processes working together, at no particular point in time is there an increase of pressure at any depth in the soil that matches the initial increase of pressure application. The research also mentions the limitations of applying the derived equations. These limitations are inherently related to the simplifying assumptions presented in the theory, as well as to the complexity of porous media. Future follow-up research is also suggested.