Study On The Method Of The Measuring Unsaturated Soil Suction

Unsaturated soil mechanics began in the 1930s,developed with the hydrology,soil mechanics and soil physics.Suction is one of the most important parameters of the characteristics of unsaturated soils,and it is also one of the most difficult parameters of unsaturated soils.The diversification of suction directly affects the permeability coefficient?shear strength and deformation characteristics of unsaturated soil.In this paper,Chengdu clay as the test object,we had analyzed different methods of test results,to make a comprehensive evaluation.Considering the test principle and characteristics of the suction test method,the filter paper method,Chilled-mirror dew-point technology and the vapor equilibrium method were used for the suction test.The filter paper method is a simple and mature technology.The test time of the Chilled-mirror dew-point technology is much short and the operation is simpler,which is a relatively new type of test method.The vapor equilibrium method can both measure the dehumidification curve and the hygroscopic curve.Chengdu clay were selected in a deep foundation pit in eastern suburbs of Chengdu.Preparing the compaction soil samples with different initial moisture content and dry densities and some flake soil samples,total were 142.In the filter paper method,the domestic double-loop type 202 filter paper was used to test the total suction and the matrix suction of the soil sample by the non-contact method and the contact method respectively.In the Chilled-mirror dew-point technology,the WP4C cold mirror dew point meter was used to test the total suction,and the matrix suction was measured combining with the CT-3031 conductivity meter.In the vapor equilibrium method,the total suction(matrix suction)was measured by 11 kinds of saturated salt solution.The hygroscopic curve was tested before the dehumidification curve.Based on the measured suction data,the soil-water characteristic curves were calculated and analyzed.By analyzing the test results of each test and comparing the test data of the three test methods,the following results were obtained:Comparing the results of the filter paper method,by the Chilled-mirror dew-point meter and conductivity meter can accurately measure the matrix suction of the soil samples.The SWCC of Chengdu clay tested by the vapor equilibrium method suggests that,in the low suction range(suction less than 70MPa)the SWCC has obvious hysteresis.The following parameters were obtained by using the VG model and Origin software to simulate the SWCC of the Chengdu clay:? = 0.4,m = 0.12056,n = 2.95337.