Experimental Research On Strength Of Unsaturated Expansive Soils

Cohesive soil often involved in water conservancy, civil engineering construction. In the anti permeability related calculation, the gradient allowed by the anti permeability of Cohesive soil mostly depended on experience.As there may be a big deviation, it will take a big potential safety hazard for the engineering construction of dam、foundation pit and so on. As a distributed material it has different with sand soil in the experimental method and the seepage failure mechanism, There is a certain theoretical and practical significance which develop cohesive soil research from the microscopic view of the experimental apparatus to seepage failure test and numerical simulation..In the dissertation I developed a new measuring instrument which is applicable to the cohesive soil seepage gradient, it consists of four part that is the pressurization system, gas water transition system, sample seepage system and Seepage monitoring system, it can effectively measured values of soil permeability allowed gradient.Using the developed instrument progress a cohesive soil seepage failure experiment which consider the factors of the degree of compaction of soil samples、clay content、particle size distribution and so on. The result shows that the impermeability of soil sample increase with the compaction of soil sample and approximately present straight linear relationship; The gradient values that seepage failure granted and the clay content in soil sample present proportional relationship, however, when clay content greater than 90% or less than 30%,clay content has no significance effect on seepage gradient; different particle size distribution has significance difference in the anti permeability of soil sample. Good particle size distribution has no related relationship with the good anti permeability of soil sample, good particle size distribution can not guarantee it has better anti permeability than that has bad particle size distribution.Based on the theory of discrete element, using particle flow software PFC2D progress a numerical simulation of the cohesive soil seepage failure ability, explain the mechanism of cohesive soil seepage failure from the microscopic point of view and compare to the experiment, the analysis of result shows that the mechanism of cohesive soil seepage failure is a tension failure which is caused by the particle bonding under high hydraulic gradient conditions、therefore it become to crack and gradually developed into a penetration channel; numerical simulation soil sample almost has the same penetration failure channel with the experimental soil sample; Under the same degree of compaction conditions, the values of Impermeability allowed gradient in.Numerical simulation has about 15% deviation compared to the result of experiment; the result of numerical simulation almost have the same values with the result of experiment, that is Impermeability allowed gradient increase with the degree of compaction. The result above reflect that the research on infiltration and sabotage of cohesive soil and far research on penetration failure mechanism.