Experimental Study On Liquefaction Process Of Saturated Sand Based On Dynamic Test Of Resistivity

Sand liquefaction is one of the typical earthquake damage phenomena in strong earthquake area.Sand liquefaction is a process of sand changing from solid state to liquid state.In the process of vibration liquefaction of saturated sand,the increase of vibration excess pore water pressure(i.e.dynamic pore water pressure)is generally considered as the mechanical mechanism leading to the evolution of sand from solid state to liquid state.However,this mechanism can not explain liquefaction phenomena such as cyclic liquidity very well.Saturated sand is a typical two-phase loose granular accumulation.It is of great significance to study the liquefaction process of saturated sand from the meso-granular and pore layers for the meso-mechanism of liquefaction of saturated sand.At present,it is difficult to observe the evolution of meso-granular or intergranular pore in saturated sandy soil,and there is still a lack of experimental research in this field at home and abroad.In order to solve this challenge,this paper introduces resistivity testing method,improves the existing dynamic triaxial equipment,studies the resistivity change of saturated sand during liquefaction,and combines the circular particle modeling and electrical test of the model to explore the pore distribution change law of saturated sand during liquefaction.The main work and achievements are as follows:1.Based on the basic principle of resistivity measurement and cyclic triaxial apparatus,an electrical testing device for saturated sand liquefaction was developed,and a method for measuring the resistivity of saturated sand samples during liquefaction was established.2.A series of liquefaction tests of saturated sand samples were carried out.Considering the influence of relative density and particle size distribution of sand,the development of dynamic pore pressure,dynamic stress-strain relationship and dynamic strength characteristics of liquefaction resistance of saturated sand during liquefaction were analyzed.3.Based on the liquefaction electrical test results of saturated sand samples,the change process of resistivity of saturated sand during liquefaction is analyzed.It is found that the resistivity of saturated sand decreases gradually in the process of liquefaction,and the reduction rate and degree are affected by relative density of sand.The influence factors of saturated sand resistivity are analyzed.It is considered that these factors will not cause the decrease of saturated sand resistivity during liquefaction.4.Based on the fact that the resistivity of sand always decreases during liquefaction,it is proposed that the homogenization of pore distribution during vibration liquefaction can lead to the decrease of resistivity,which is verified by the electrical test of circular particle model.Firstly,based on Voronoi-Delaunay nesting,a series of circular particle models with uniform pore distribution are established,and the homogenization process of the pore distribution of the circular particle model is tested.It is found that the more uniform the pore distribution of the circular particle model is,the smaller the resistivity is,and the particle size does not affect the existence of this linear relationship.5.In conclusion,it is considered that the process of liquefaction of saturated sandy soil is a process of gradual homogenization of pore distribution of sandy soil.