Experimental Study On Unsaturated Dynamic Strength Characteristics Under Cyclic Loading For Chuanxi Gravel Mixed Soil

In a complex geological environment of the mountains of southwest in China are widely distributed a kind of gravel mixed soil, with many origins, various compositions, multiple gradations, complex particle morphology and environment sensitivity. In structure, highway subgrade, railway subgrade and bridge structure foundation which is composed of the soil, there is the phenomenon of large area of instability under earthquake load, which caused huge economic loss. The geological exploration showed that most of these gavel soil was in the unsaturated state. Therefore, to the nature slope, high embankment, highway and railway subgrade, structure foundation and earth-rock dams which is composed of the unsaturated gravel mixed soil in western sichuan mountainous area and even the entire southwest region, it has the important theoretical and engineering applicable value to research the dynamic strength characteristics of the unsaturated gravel mixed soil under cyclic load. In this paper, the idea can be summarized as "physical form-matric suction-unsaturated shear strength-dyamic unsaturated strength". We dicided to control the suction and to do a large number of experimental studies around the idea. And then, we studied the dynamic strength characteristics of unsaturated soil, which is based on the theoretical analysis of the date and analysis of the influence factors and influence mechanism. The main contents and conclusions are as follows:(1) By carrying out experiments on the identification of mineral composition, analyzing grain composition, moisture content and density test of the two types of undisturbedgravel mixed soil taken back in different places, we found that these two kinds of soil differ in physical form.(2) By perfoming soil-water characteristic experiment on the unsaturated mixed soil with pressure plate test combining with filter paper test, we could find that soil physical form has a great influence on soil water characteristic curve, which is mainly associated with the soil composition of particle structure and pore size.(3)By doing unsaturated triaxial testing based on the soil-water characteristic curve, we found that suction’s contribution to the shear strength of the soil was mainly manifested in the improvement of cohesive force in unsaturated gravel soil.(4) Having selected the same water content as the static triaxial testing, and having done unsaturated dynamic triaxial testing, we found that the suction of the soil had obvious contribution to increase the dynamic strength.(5)Having analyzed the relationship between the static strength and the dynamic strength and done normalization processing to dynamic strength used static strength of unsaturated soil, we found that there were obvious regularities between the static strength and dynamic strength of the unsaturated gravel mixed soil. At last, we got the expression for the normalized dynamic strength curve through the analysis of fitting the curve.