Study On Resistivity Variation Characteristics Of Saturated Sand Samples During Liquefaction

Sand liquefaction,as one of the typical site earthquake disasters,may cause engineering problems such as ground instability,building subsidence and slope sliding.It is an important means to understand the liquefaction mechanism to carry out unit tests on the liquefaction strength of sand samples,and many tests have been carried out by scholars at home and abroad.The existing laboratory test methods for the liquefaction of sand are based on the continuum mechanics point of view,without considering the change of sand structure.At present,discrete element numerical simulation method is mainly used to study the change rule of saturated sand structure in liquefaction process,so it is very necessary to test and verify.Based on the independently developed dynamic triaxial liquefaction electrical measuring equipment,this thesis carried out an electrical testing test of saturated sand liquefaction by using AC resistivity testing technology and cyclic triaxial liquefaction test.By analyzing the resistivity variation characteristics of saturated sand samples during the liquefaction process,the changes in the pore structure of saturated sand were explored,and the liquefaction mechanism of sand was explored from the perspective of pore reconstruction.The main work and achievements of this thesis are as follows:(1)Carry out electrical impedance tests of different pore liquid ion concentrations,power supply frequency,saturation and particle size for sand samples in static state,and analyze the changes in resistivity obtained.The results show that the ion concentration in the pore fluid of sand has a great influence on the resistivity.In the test range,the resistivity of sand decreases with the increase of saturation,pore fluid ion concentration,particle size and power frequency,and the resistivity and saturation show a power function relationship.Based on the signal test of pure resistance components under different voltage amplitudes,the higher the voltage value,the less noise signal is given.The results of the test signal of the pure resistance element under different voltages are given.The larger the voltage,the smaller the amplitude fluctuation of the test signal and the closer to the real resistance value.(2)Based on the view that the change of resistivity can reflect the change of pore structure of saturated sand,in order to reduce the influence of equipment error on the electrical measurement results,the liquefaction electrical measurement equipment was optimized and improved,the sensor coefficient was re-calibrated,the factors affecting the liquefaction electrical measurement test were analyzed and the test plan was developed.(3)Based on the electric test results of saturated sand liquefaction,the development law of dynamic stress,dynamic strain and dynamic pore pressure is analyzed,and the relative density and particle are analyzed.(4)Based on the resistivity cosine calculation model proposed by the research group,the change of resistivity of saturated sand samples in the liquefaction process was analyzed,revealing that the resistivity of samples in the liquefaction process showed an overall decreasing trend.The test results show that the resistivity of samples during liquefaction can reflect the change of pore structure of sand well.The resistivity and dynamic stress are similar to "hysteresis loop" in general,and the linear density can reflect the speed of pore structure change in the liquefaction process.The relationship between resistivity and dynamic strain decreases linearly from the early phase of liquefaction vibration to the "cyclic oblique line" after liquefaction vibration.Before the initial liquefaction,the dynamic pore pressure increases and the resistivity decreases,which has a good correlation.After the initial liquefaction,the dynamic pore pressure remained unchanged,lost its symbolic significance,and the resistivity continued to decrease.The change of resistivity at the end of the cycle corresponds to the development law of pore pressure ratio at each stage.The change of pore structure can be quantitatively analyzed by the change of resistivity at the end of the cycle.