Influence of Matric Suction on Shear Strength Behavior of Unsaturated Silty Sand

In order to research matrix suction how to influence the shear strengt of unsaturated silty sand. Based on the analysis of the Soil-water characteristic of unsaturated silty sand through pressure plate instrument test,the suction control direct shear tests under the different suction condition of unsaturated silty sand are studied. And then, the microscopic structure of two kinds soil sample with different water content are scanned to analyze the relationship between the matrix suction and the shear strengt of unsaturated silty sand. The results of the research show that unsaturated silty sand different from unsaturated clayey soil.When water content gradually reduce, the soil shear strength of unsaturated silty sand is not always increased with the increase of matrix suction, but there is a "peak effect".The appearance of "peak effect" is due to unsaturated silty sand has own microstructure characteristics.On the other hand, when the moisture content reduction constantly,the existence form of moisture change gradually.The two factors lead to the effect area of matrix suction change constantly,and then influence shear strengt of unsaturated silty sand to appear "peak effect". In addition,the stress environment also can influence contribution degree of matrix suction to the shear strengt of unsaturated silty sand.