Study On Rapid Determination Method Of Soil-water Characteristic Curve And Hydraulic Conductivity In Full Suction Range

Most of the soils involved in nature and practical engineering are in unsaturated state,but the first thing to solve in the study of unsaturated soil is the change of hydraulic properties caused by the change of matrix suction or saturation,such as soil-water characteristic curve and permeability coefficient function.Soil-water characteristic curve and permeability coefficient function are of great significance for predicting and analyzing the water holding capacity,permeability,deformation and strength of unsaturated soil.however,the soil-water characteristic curve and permeability coefficient function in a full(wide)suction range are very time-consuming,often for several months,due to the limitation of test conditions(soil water potential sensor is difficult to measure high suction).It is difficult to measure the permeability coefficient function in the full(wide)suction range while measuring the soil-water characteristic curve.In order to solve the problem of rapid determination of soil-water characteristic curve in the wide suction range,a joint determination method of soil-water characteristic curve is proposed in this paper,which combines pressure plate method,parallel filter paper method and dew point water potential meter,and gives full play to the advantages of different methods to quickly measure the suction of Lanzhou silt in different ranges.Among them,the pressure plate method is used to measure the low suction section(0～50 k Pa),the filter paper method is used to measure the middle suction section(50～10~3 k Pa),and the dew point potentiometer is used to measure the high suction section(10~3～10~5 k Pa).The combination of the three test methods can quickly determine the soil-water characteristic curve in the wide suction range of soil,and it is proved that this method is suitable for different soil types by using Qinghai silty clay and Gaomiaozi bentonite.The experimental results show that:(1)The test results of the saturated parallel filter paper method and the serial filter paper method are in good agreement,so the saturated parallel filter paper method can be used instead of the serial filter paper method to shorten the measuring time;(2)the combined determination method of soil-water characteristic curve can shorten the measuring time of soil-water characteristic curve from several months to 7 days.The joint determination method of soil-water characteristic curve proposed in this paper realizes the rapid and accurate determination of soil-water characteristic curve in a full(wide)suction range,which is expected to make the measurement of soil-water characteristic curve a conventional geotechnical test.On the basis of solving the rapid determination of soil-water characteristic curve in the full(wide)suction range,in order to realize the rapid determination of permeability coefficient function in the wide suction range,this paper puts forward a joint determination method of permeability coefficient,which combines the wetting front advance method with the instantaneous profile method,in which the wetting front advance method is used to determine the permeability coefficient in the high suction stage and the instantaneous profile method is used to determine the permeability coefficient in the low suction stage.The feasibility and applicability of the combined determination method were studied by using Qinghai silty clay,Lanzhou silt,Gaomiaozi bentonite and standard sand.at the same time,the error sources,applicable scope and applicable soil types of the two methods are discussed in detail.The results show that the joint determination method of permeability coefficient proposed in this paper can realize the rapid determination of permeability coefficient function in the wide suction range of the same group of soil columns,and this method is suitable for different soil types,which is expected to make the measurement of permeability coefficient function of unsaturated soil a routine test in unsaturated soil mechanics.After verifying the feasibility and applicability of the joint determination method of SHCF,this paper also used the joint determination method of permeability coefficient to explore the effects of different dry density,initial moisture content,water migration mode and soil quality on SHCF in the wide suction range.