Research On Relationship Between Soil-Water Characteristic And Shear Strength Of Nanning Unsaturated Expansive Soil

In this dissertation, the soil-water characteristic curve and shear strength properties of Nanning unsaturated expansive soil are researched by laboratory test. The purposes are to provide a theoretical basis for construction of the high-speed railway constructed in unsaturated expansive soil area. Through laboratory test, the boundary effect zone and transition zone of soil-water characteristic curve were measured, the hysteresis loop of soil-water characteristic curve was found. Then, the mathematical representation of the soil-water characteristic curve can be fitted by Fredlund and Xing model, the fitting parameter a is 65kPa, n is 4.449 and m is 0.967.According to the Nanning unsaturated expansive soil samples with different moisture content, Direct Shear Test and Triaxial Shear Test were carried. During the test, plasticity damage occurred for all samples. The shear strength decreases with the increase of moisture content. The stress-strain curve presents a regularity trend of slowing down when moisture content increase and confining pressure reduce. The shear strength parameters are measured. For the Direct Shear Test Φ’ is 22.734°; c’ is 34.753kPa;Φb is 18.315°. For the Triaxial Shear Test Φ’ is 17.437°; c’ is 25.917kPa; Φb is 9.676°Measured the swelling pressure for the different initial moisture content sample by the zero swell tests. The test results show that the swell pressure decreases with increasing initial moisture content. Mathematically defining the relationship between swelling pressure and initial matric suction, an exponential function can be used. While the fitting parameter a is 3.841; b is 0.01168. Moreover, logarithmic function can be used to best-fit data obtained from relation curve for suctional strength and swelling pressure. For the Direct Shear Test, the fitting parameter a is 27.043; b is 0.248. While for the Triaxial Shear Test the fitting parameter a is 13.929; b is 0.248.Finally, contrast analysis of the relationship between the indicators, a revising method using swelling pressure instead of matric suction characterize shear strength of unsaturated expansive soil was defined. The revised shear strength parameters of Nanning unsaturated expansive soil were found. τf=c’+(σ-ua)tanΦ’+Alg(λPs)...