Particle-based hydro-mechanical analysis of saturated granular soils

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Li, Bo
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Electronic thesis
Civil engineering
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Saturated granular media are multi-phase mixtures of mineral particles, forming a random porous matrix, and water filling the pores. The coupled response of these phases engenders a broad range of response patterns that distinguish these media from both solids and fluids. Liquefaction of saturated granular soils is a pervasive problem that caused major damages to the civil infrastructures during all recent major earthquakes. Numerous sophisticated continuum models were developed over the last few decades to predict soil liquefaction and its effect on the civil infrastructure. A number of studies were successfully conducted using a continuum-discrete model of the hydro-mechanical response of saturated granular media. Many of these models have not been calibrated or validated. This study presents a report on calibration and analysis (C&A) exercise that was undertaken to assess the performance of a continuum-discrete hydro-mechanical soil liquefaction model. This model is based on a coupled formulation of a discrete element model (DEM) of the solid phase and a volume-averaged Navier-Stokes (VANS) model of the fluid phase. The C&A exercise was performed using the experimental results of several small-scale centrifuge tests of a saturated sloping deposit that was tested within the context of the Liquefaction Experiments and Analysis Projects (LEAP). The conducted analyses showed that a model using a weakly compressible version of the VANS equations provides more reasonable predictions that fit better the observed experimental results while using realistic values of particle stiffness and pore fluid viscosity. This study also addressed other aspects associated with centrifuge testing, namely the effects of an artificial radial gravity field and the impact of sensors. These issues cannot be verified easily by physical testing, while the discrete element method provides a powerful tool in this regard. A series of DEM simulations were performed for a model corresponding to a centrifuge test of a dry sandy slope. The obtained results show that a radial centrifugal force field induces a lower confining within the middle zone of the centrifuge model, and also leads to larger permanent displacements under dynamic loading. These differences are partially counteracted by using a curved slope surface., The effects of embedded sensors in a dry sandy slope were found to be relatively small and generally acceptable form an engineering perspective. However, these sensors behave as soil reinforcement that reduces the permanent sliding of the slope for extreme conditions of very small soil models under very high centrifugal gravity field. Multiple aspects including sensor size, arrangement, and input motion were found to affect the response differently. The continuum-discrete model capabilities were also extended to handle complex geometrical and material properties using the Lattice Boltzmann method (LBM). This method employs fine lattice meshes and is highly effective in accommodated complex conditions while being computationally efficient. In this study, the LBM was adjusted and adapted to solve the VANS equations. A novel pressure correction term is introduced to ensure the solution accuracy and stability at the interface between zones of highly dissimilar permeabilities. A new mass-source term is employed to assure an accurate and stable solution to dynamic problems in which the soil porosity varies with time. A verification analysis showed that the developed LBM solutions to the VANS equation closely match the analytical solutions for selected benchmark problems.
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Rensselaer Polytechnic Institute, Troy, NY
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