| Unsaturated soil distributes widely in nature. In geotechnical engineering activities, most of soil is unsaturated. There is gas in unsaturated soil which makes its nature becomes more complicated. With unsaturated soil engineering problems appeared, mechanics and engineering characteristics of unsaturated soil have been the intense studying interest in the field of geotechnical engineering. At present, the theory research of saturated soil is relatively perfect, the theory of unsaturated soil is still at the stage of development, unsaturated soil problem is still using the saturated soil theory to solve, which brings errors to engineering design and practice inevitably. In the theory research of unsaturated soil, the impact on its properties of saturation and matrix suction is research emphasis.In this paper take typical silt at Yang Zhou for study, getting the samples of remolded soils, a series of tests were carried out under soil-water characteristic curve, conventional triaxial tests, unsaturated triaxial tests. Through the test results, do comparative analysis of stress strain properties and shear strength index on the saturated and unsaturated soil samples, and do further analysis on contributes of matrix suction and saturation to unsaturated soil shear strength. The results showed that:Matrix suction has little influence on effective angle of internal friction of specimen, while has a great influence on failure modes and cohesion. With the increasing of matrix suction, stress-strain translates from hardening type to softening type. With the increasing of matrix suction, effective internal friction angle changes little and is approximately equal to the effective internal friction angle of saturated soil. With the increasing of matrix suction, cohesion is significantly improved. Matrix suction friction angle φb is not a constant, when matrix suction is less than100kPa,φb decreases with matrix suction increasing, and the rate of decrease reduces gradually; when matrix suction is greater than100Pa,φb tends to a fixed value. The tests results are consistent to modified Fredlund strength theory. Make numerical simulation of soil slope stability by finite element program ABAQUS to get soil slope stability factor of safety. Simulation results further confirmed impact on soil shear strength of matrix suction and saturation, the trend of attenuation about soil slope factor of safety is similar as the change of the shear strength. |
