Coupled Field Equations for Saturated Soils and Its Application to Piezocone Penetration and Shield Tunneling.
Date of Award
Doctor of Philosophy (PhD)
Civil and Environmental Engineering
George Z. Voyiadjis
An elasto-plastic coupled system of equations are formulated here in order to describe the time-dependent deformation of saturated cohesive soils. Formulation of these equations is based on the principle of virtual work and the theory of mixtures for inelastic porous media as proposed by Prevost (1980) and Kiousis and Voyiadjis (1988). The saturated soil is considered as a mixture consisting of two deformable media, the solid grains and the water. Each medium is regarded as a continuum and follows its own motion. The coupled equations are developed for large deformations with finite strains in an updated Lagrangian reference frame. The coupled behavior of the two phase material is implemented into the finite element program GAP/CTM (Geotechnical Analysis Program based on the Coupled Theory of Mixtures), which is developed by the author. This formulation is applied in the analysis of two geotechnical problems. The piezocone penetration and the shield tunneling in cohesive soils. The piezocone penetration in cohesive soils is numerically simulated and implemented into the finite element program (GAP/CTM). The continuous penetration of the cone is simulated by applying an incremental vertical movement of the cone tip boundary. The numerical simulation is done for two cases. In the first case, the interface friction between the soil and the piezocone penetrometer is neglected. In the second case, interface friction is assumed between the soil and the piezocone. Results obtained from the simulation using the proposed model are compared with those obtained from the miniature piezocone penetration tests (PCPT) for cohesive soil specimens conducted at the LSU calibration chamber. The resulting excess pore pressure distribution and its dissipation using the numerical model are compared with some available predicting methods. A two-dimensional computational model is developed in order to simulate the continuous advance of the Earth Pressure Balance (EPB) Shield during the tunneling process in cohesive soils. This model is implemented into the finite element program (GAP/CTM). The computational model is based on the plane strain "transverse-longitudinal" sections that can incorporate the three-dimensional deformation of the soil around and ahead of the shield face. The continuous shield advance is modeled using the remeshing technique. This model has been used to analyze the N-2 tunnel project constructed in 1981 in San Francisco, California.
Abu-farsakh, Murad Yusuf, "Coupled Field Equations for Saturated Soils and Its Application to Piezocone Penetration and Shield Tunneling." (1997). LSU Historical Dissertations and Theses. 6535.