Study On Permeability And Deformation Characteristics Of Saturated Sands Under Low Effective Stress

China is a frequently earthquake-attacked nation.The problem of liquefaction ofsaturated sand caused by the earthquake is one of hot and difficult topics in theresearch of geotechnical engineering. Many results have been widely recognisedabout the generation mechanism and the impact factors of the sand liquefaction, andevaluate of the liquefaction potential. While the stress-strain behavior of soils underthe low effective stress state have not been well defined. And the existing researcheshave little or no consideration about the process with the diffusion and dissipation ofexcess pore pressure. Based on this, the seepage and deformation charateristics of soilunder low effective stress are studied in detail by means of a series of laboratoryexperiments and numerical simulation. The main contents of the current research areas follows:(1) A novel apparatus was developed based on the soil reconsolidation theory andcombined with the mechanism of sand boil. It is an improvement of the conventionalconstant head permeability test device. The apparatus can be used for measuring thepermeability under low effective stress. And its usage and test procedures areintroduced in detail.(2) Using new apparatus test device, the permeability characteristics of threekinds of different particle size distribution of sand is studied. The study found thattheir permeability coefficients have different degrees of increase when the effectivestress is equal to zero. The variation of Xu zhou sand is the largest, about4times aslarge as before;1#sand is about2.5times as large as before;2#sand is about1.5times as large as before. The permeability coefficient of sand decreases with theincrease of effective stress.(3) Using automatic triaxial apparatus to simulate saturated sand under loweffective stresses in the static loading process. The result shows that the stress straincurve can be divided into three stages under the different effective stress state,including low strength stage strength of the recovery stage and strain-softeningstage.We also studied the influence on the development trend of the stress-strain curvewith different of initial relative density and degree of liquefaction and embedmentdepth of soil layer.(4) Combining with the results of triaxial test and permeability test, in this paper, the low stress state is defined as the effective stress state when the ratio betweeneffective stress and the initial effective stress less than50%.(5) The research results of permeability and deformation characteristics of soilunder low dffective stress are applied to the analysis of numerical simulation. And thestability of the sand slope safety under the effect of pore water pressure with porewater seepage from bottom to top is studied.