Study On Rapid Measurement Method Of Unsaturated Soil Permeability Coefficient Based On Van Der Pauw Method

The permeability coefficient of unsaturated soil is an important parameter for the analysis of landslides,foundation expansion,dam burst and other diseases.It is of great value to quickly measure the permeability coefficient of unsaturated soil.At present,transient method and steady state method are commonly used to measure the permeability coefficient of unsaturated soil.However,due to the large size of the sensor and the slow speed of suction test.At present,problems such as large volume and long suction test time generally exist in measuring device of permeability coefficient of unsaturated soil.These issues cannot meet the needs of the actual project.Therefore,it is of great significance to explore a fast,convenient and miniaturized test method for the permeability coefficient of unsaturated soil.The main contents of this thesis are as follows:(1)A set of rapid measuring device for soil water characteristic curve was developed.Compared with the ceramic plate,nylon porous filter membrane has thinner thickness and faster seepage velocity.Nylon porous filter membrane was introduced to realize the function of the ceramic plate.The matric suction balance velocity was improved and the test time was shortened.Rapid measurement of the soil water characteristic curve was realized.Soil water characteristic curves of sand and loess were measured by the device.The basic data for the calculation of unsaturated soil permeability coefficient was provided.(2)A set of rapid measuring device for permeability coefficient of unsaturated soil was designed.Van der Pauw method is non-invasive and can measure the moisture content of small volume samples.With expanded van der Pauw method,the speed of unsaturated permeability test is improved and the miniaturization of the test device is realized.In order to meet the test conditions of the extended van der Pauw method,the calculation method of permeability coefficient of multi section transient profile was optimized.A set of joint measurement and calculation method of permeability coefficient of unsaturated soil was formed.Based on this,a set of unsaturated soil permeability coefficient measuring device was developed.The rapid,nondestructive and automatic measurement of unsaturated soil permeability coefficient is realized.(3)The test method of unsaturated permeability coefficient was improved.Unsaturated permeability tests were carried out on loess and sandy soil respectively.It was found that there is obvious ion migration phenomenon in the process of permeability test.The calculation method of water content during soaking process based on van der Pauw method was proposed.Therefore,the influence of ion migration on the accuracy of the test device is weakened.To improve the calculation accuracy of unsaturated permeability coefficient,the curve model of water content changing with time during soaking process was improved.Finally,the unsaturated permeability coefficient was calculated according to the instantaneous profile method.The accuracy of the device was verified by comparative tests.