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Two suggestions are provided for expanding the scope of LEAP project for the next stage. The first suggestion is to perform undrained cyclic shear tests with addditional static deviator stress to represent more realistic stress conditions in soil-structure systems during earthquakes. The other suggestion is to perform centrifuge model tests with non-homogeneous soil layer such as mildly sloping ground of liquefiable sand overlain by a less permeable capping crust layer, leading to a unlimited flow failure of surface crust. Effects of void ratio redistribution and seepage flow will be studied in detail in this type of cetrifuge tests.

Migration of fine particles within internally unstable granular soils under water seepage flow (suffusion) is one of the most common causes of earth infrastructures’ failure. To assess the ability of Microbial Induced Calcite Precipitation (MICP) to prevent the segregation in an internally unstable soil, internal erosion tests were conducted upon soil samples treated by bacteria and cementation solutions. MICP experiments were carried out with concentrations of urea/CaCl2 equal to 1.4 M. Volumes of injected bacteria solutions were equal to the volumetric water content corresponding to different tested degrees of saturation (Sr): 30, 60 and 80%. Cementation solutions were injected three times for each sample. Biochemical properties of MICP were examined to predict bacterial movement through soil matrices as a function of Sr. The amount of the CaCO3 produced was examined depending on Sr. Following their treatment, samples were saturated and submitted to increment of hydraulic gradients varying from 0.1 to 10. Eroded fine particles masses, seepage flow rates and effective hydraulic gradients along samples were measured throughout the experiment. The results of our study pointed out that MICP stabilized internally unstable granular soils as the critical gradient went from 0.7 for untreated samples to 5 for biocemented samples.

In this study, a centrifuge model tests and effective stress analyses are performed on a breakwater subject to Tsunami such as those seriously damaged during 2011 East Japan Earthquake (Magnitude 9.0). The centrifuge model tests at a scale of 1/200 are performed to simulate the failure of a breakwater subject to Tsunami. With the effective stress analyses, this study demonstrates the importance of the mechanism of failure in the rubble mound due to seepage flow of pore water in addition to the force of Tsunami action., Perspectives on Earthquake Geotechnical Engineering

Numerical simulation of coupled hydromechanical processes is crucial to address many problems in geotechnical engineering. Conventionally, the seepage flow equation in a hydromechanical model is solved by the continuous Galerkin (CG) finite element method. However, the CG method does not ensure mass conservation in a local (element-wise) manner, which may be a critical drawback in a number of situations. Here we introduce an enriched Galerkin (EG) finite element method that allows locally mass conservative simulation of coupled hydromechanical problems. The major advantage of the EG method is that its computational cost is appreciably less than that of the discontinuous Galerkin (DG) method. We describe the proposed method’s key idea and demonstrate its performance and significance through an example simulation of wetting collapse of a heterogeneous unsaturated soil.

This work presents a short account of some recent advances in the numerical simulation of backward erosion piping, accomplished in the framework of a collaborative research between Italian and French research groups. After a brief review of the state of the art in engineering practice and research, we outline the key points of a novel approach and show some of the results obtained in an extensive validation work.

Two-phase flow model, modified Mohr-Coulomb model and the theory of unsaturated soil are adopt in FLAC, and then the characteristics of seepage flow of Beichuan soil under rainfall conditions are numerically simulated. It is shown that the initiation of rainfall-induced debris flow is affected by rainfall density and duration. The maximum horizontal displacement occurs at the foot of the slope and increases with rainfall duration. The vertical displacement is non-uniform and the maximum value occurs at point A, which is at the top of two-third. Whether or not a sudden change of displacement occurs at the characteristic point A is suggested to judge if debris flow starts. It is also shown there is a good agreement between numerical simulation results and rainfall model test data in laboratory.