| Most of the soil in nature is in an unsaturated state.When the matrix suction(or water content)changes,the strength,deformation and permeability of the soil will also change.The unsaturated triaxial test is an important means to study the mechanical properties of unsaturated soil,and the gas-liquid equilibrium is an important part of the unsaturated soil triaxial test,and the water migration in the soil under a given air pressure makes the matrix suction in the soil sample reach the set value.It is of great significance to develop a method suitable for soil water migration test in the narrow space of triaxial test for determining the gas-liquid equilibrium(matric suction reaches the set value)of unsaturated triaxial test.At the same time,unsaturated permeability coefficient is an important parameter for studying the unsaturated soil mechanics.Based on the instantaneous profile method,water migration testing technology is used to test soil permeability coefficient in the process of gas-liquid equilibrium,which can not only expand the application scene of triaxial apparatus,but also reflect the influence of stress state on permeability coefficient.Therefore,it is of great significance to establish an accurate testing technology and method for water migration of triaxial samples in the process of triaxial test.The main research contents are as follows:1)A gas-liquid-electric coupling model is established to simulate the water cut test in the gas water balance stage,the relationship between the water content distribution and the resistivity test value of soil samples is grasped,and the influence range and the maximum test error of van der Pauw(vd P)method for measuring water content of triaxial samples are clarified.2)A three row resistivity testing device for soil samples in triaxial pressure chamber based on vd P method is developed,and the soil samples resistivity test during triaxial test is realized.Through calibration experiment and sensitivity factor test,the testing accuracy,operating conditions and error correction method of the device are clarified: the test results show that the resistivity testing accuracy is ± 1%;Before the test,the net confining pressure shall not be less than 120 k Pa,and the net confining pressure shall be kept above 20 k Pa during use to ensure that the electrode is in full contact with the soil sample;For the measurement error caused by temperature change,Campbell resistivity-temperature model can be used for correction.3)The water migration and unsaturated permeability coefficient in triaxial air water balance test were tested.It includes two water inlet and drainage cycles under the control of matrix suction,and the water content distribution of soil samples at each stage is tested respectively.The results show that,due to the influence of ion migration and ion diffusion in pore water,the water content of soil sample cannot be accurately calculated only by resistivity during the process of water inflow;In the process of drainage,the phenomenon of ion migration and ion diffusion is not obvious.Compared with the drying method,the maximum relative error of this method is 3.4%;On this basis,based on the transient profile method,combined with the soil water characteristic curve,the unsaturated permeability coefficient of loess is calculated and compared with the permeability coefficient of loess measured by Hu Haijun,which has a high consistency. |
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