Evolution Of Engineering Characteristics And Slope Stability Of Expansive Soil Under Wetting-drying Cycles

A series of indoor experiments were conducted on Pukou expansive soil as the research object,including direct shear tests,unconfined compression tests and penetration tests,analyzing the characterize strength,permeability,crack development of expansive soil during wetting-drying cycles.Digital processing technology and CT scanning were used to analyze quantitatively crack development on perspective of 2D and 3D,discussing how crack affect engineering characteristics under w-d cycles.Based above previous research,establishing slope model and taking numerical analysis by Geo-Studio software slope/W and the seep/W module,discussing crack and w-d cycles on expansive soil influenced slope stability.The main research contents and results are as follows:(1)Relationship between strength and w-d cycles was discussed through direct shear test and unconfined compression test,during drying,shear strength,unconfined compression strength,shear strength parameters(cohesion and internal friction angle)increase with decreasing water content;during the three drying paths,both the shear strength and cohesion increase first and then decrease,and they reach peak value at the second dying path.However,the internal friction angle is slightly influenced by wetting-drying cycles,and unconfined compression strength decreases gradually.(2)Quantitatively analyzing crack development of shear and unconfined compressive texts with digital image technology,presenting the quantitative crack index(fracture rate,crack length,average width and crack number)to evaluate the development degree of cracks,and exploring the effect of w-d cycles,deeply discussing the relationship between crack development and strength.Based on above,using shear strength of theory of unsaturated soil,analyzing the ratio of strength of crack sample and no crack sample,namely reduction coefficient,and studying the quantitative relationship between crack development and strength reduction coefficient.(3)Experiments were conducted on unsaturated soil to study permeability changes w-d cycles,observing infiltration intensity variation during unsaturated stage,discussing crack development influence permeability,the result shows initial infiltration weaker with lower water content during first drying process,but the stronger during other drying process;with the increase of the W-d cycles,saturated permeability coefficient and unsaturated initial infiltration intensity increased.(4)CT scanning technique is applied to observe inner crack development during drying process,reconstructing 3D model based on Matlab and quantitatively analyzing,finding volume crack rate increases first and then decreases with water content decrease.(5)Numerical analysis of expansive soil slope are took by slope/W and the seep/W module of Geo-Studio software to explore slope stability during w-d cycles,considering several engineering condition including crack,different crack depth and rainfall condition.Result shows that crack can partially attenuated slope stability,crack development is relatively deep,the safety factor is low;safety factor of slope decrease under the condition of rainfall;with the increase of number of cycles,safety factor of expansive soil slope decreases.