Study On Variation Characteristics Of Resistivity Of Saturated Sand During Liquefaction

Liquefaction of sand is one of the common seismic disasters,which can cause catastrophic damage to the site,such as large deformation,differential settlement and slope sliding.Unfortunately,according to the existing liquefaction mechanism,it is difficult to describe the behavior of liquefiable soil composed of cohesionless discrete soil particles accurately and comprehensively.Based on the deficiency of the liquefaction mechanism,this thesis intends to analyze the change of pore structure from the perspective of the change of resistivity of saturated sand during the liquefaction process.With the support of the National Natural Science Foundation of China "Research on the Void Redistribution Mechanism of Saturated Sand during the Whole Process of Vibration Liquefaction"(No.51978317),the resistivity testing of sand liquefaction was carried out by using the resistivity test method of AC current and combined with the dynamic triaxial test.The resistivity change law of saturated sand during liquefaction process is studied,which lays a foundation for the study of pore structure change(void redistribution)law of sand liquefaction in the later stage.The main work and conclusions are as follows:(1)In order to accurately measure the resistivity change caused by the change of pore structure,the dynamic triaxial apparatus and the resistivity apparatus are improved,and the optimum salt content of pore liquid is determined to reduce the noise of resistivity test signal.(2)The impedance characteristics of saturated sand with different porosity and particle size were studied by the AC resistivity method.The results show that the resistivity of saturated sand with different particle sizes decreases as a power exponential function with the increase of porosity,and the impedance Angle decreases linearly with the increase of porosity(3)Based on the test results of dynamic stress,dynamic strain and excess pore water pressure(dynamic pore pressure)during the liquefaction of saturated sand,the influence laws of relative density and particle size on the development of dynamic pore pressure and dynamic strength of saturated sands,and also the development characteristics of dynamic stress-strain relationship are analyzed and compared with the previous research results.The dynamic response of saturated sand reflects the basic mechanical behavior of liquefaction of saturated sand.(4)The calculation model and method of resistivity of saturated sand under cyclic load are established and the variation law of resistivity of saturated sand during liquefaction is studied.It is preliminarily revealed that the resistivity of saturated sand decreases gradually during liquefaction.The results show that:(1)Resistivity decreases with the increase of pore pressure before initial liquefaction,which has a good corresponding relationship;After initial liquefaction,resistivity continues to decrease while dynamic pore pressure remains basically unchanged.Resistivity may results reflect more information about pore structure changes in saturated sand than dynamic pore pressure.(2)Under the same conditions,the higher the relative density of the sample and the greater the applied dynamic stress are,the smaller the decrease in resistivity is.