Investigation On Mechanism Of Local Deformation Due To Pore Water Flow

Seismic liquefaction is one of the natural disasters causing the failure or destruction of buildings(structures).Liquefaction is a process that excess pore water pressure increase,effective stress decrease,and may generate deformation or large deformation with the soil strength reduction and even completely losing.Liquefiable soil is always considered as a homogeneous isotropic medium.However,within the large layer thickness of saturated sand,it will generate excess pore pressure gradient inside sand due to the excess pore pressure created by earthquake has great differences in space and time,and result in pore water flowing.Sand properties will produce great location differences because of the directional pore water flowing,under the same initial stress conditions,the local sand units which mechanical properties become weak are likely to have obvious shear strain location.But the above is only speculation,because of mesoscopic pore water flow is difficult to be observed and analyzed,relevant research is very lack.Aim at those challenges,adopting the resistivity test method,creating the conductivity and permeability multi-function testing equipment,carrying out one dimensional impact soil liquefaction tests based on electrical measuring,and combining with theoretical analysis,the main work and results are as follows:1.Design and making the testing equipment named soil conductivity and permeability multi-function testing equipment to study the relationship between permeability coefficient and formation factor;2.Carrying out one dimensional impact soil liquefaction tests based on electrical measuring;Observing and descripting common(such as sand boiling)and uncommon(such as particle migration,local water film)sand liquefaction phenomena;3.Analyzing the response process of resistivity in different buried depth during the impact liquefaction process,and the relationship with the development process of excess pore pressure and dividing the phases;4.According to the test of the resistivity test results,and combining with the relationship between permeability coefficient and formation factor,thinks that there are the mesoscopic void redistribution due to pore water flowing during soil liquefaction process,and shows that permeability coefficient increases firstly and then decreases,and its biggest values are 1.1 ~ 1.4 times of initial permeability coefficient,resulting in regional difference;5.Analyzing the mechanism of local shear strain due to pore water flow according to the relationship between shear modulus with effective stress and porosity.