Study On Instantaneous Profile Method Of Permeability Coefficient Of Unsaturated Soil By VDP Method

Transient profile method is a common method for measuring the permeability coefficient of unsaturated soil,it refers to determining the volumetric water content and matrix suction of soil samples along different directions of water flow during transient transient test to determine the flow velocity and hydraulic gradient.The permeability coefficient can be determined by the ratio of the flow rate to the corresponding hydraulic gradient.The test instrument required by the method is simple and convenient to operate,and is the most commonly used method for measuring the permeability coefficient of unsaturated soil.However,during the test,the water content and the matrix suction probe are larger,so the soil sample requirements are larger,resulting in longer penetration time;and the probe is inserted into the soil sample,which affects the integrity of the soil sample.Therefore,the development of a test method that is miniaturized and does not affect the integrity of soil samples is of great value for improving test accuracy and speeding up the test process.In this paper,the van der Pauw method is used to measure the resistivity and has the advantages of high precision,stable test and no interference to soil samples.A new non-saturated soil permeability coefficient test device has been developed,which is used to carry out indoor penetration test and soil water characteristic curve.The experimental research verified the applicability and accuracy of the test device and provided technical support for engineering practice.The following are the main contents and research results of this article.(1)Using the numerical computation method,the height range of the electric field-affected sample during the resistivity test based on the van der Pauw method is determined.Based on this,a small-volume non-saturated soil permeability coefficient test device is developed.(2)Soil-water characteristic curve test and permeability test were carried out on different kinds of soils,and the variation of matrix suction with volumetric water content was obtained.The influence of ion migration with infiltration liquid on resistivity test results was discussed and obtained at different positions.The resistivity changes at different times,the results were normalized,and the change of volumetric water content with time was obtained,which further verified the wide applicability of the device.(3)According to the soil-water characteristic curve test and the results of the permeability test,the permeability coefficient of the unsaturated soil of the three soils was calculated by the principle of transient profile method,and the calculation results were compared with the results of the unsaturated soil permeability coefficient predicted by the VG model to verify the test.The accuracy of the device.