Strength and Deformation Characteristics of Silty Sand improved by Gravel

Silty sand is a poor filler of highway and railway subgrade, and various physical and chemical improving methods have been applied to increase the strength and stability of silty sand. Adding gravel to silty sand is a routine physical improving method. In this paper, large-scale triaxial tests were carried out on silty sand and improved soil which is obtained by adding 4 different proportions of gravel into the silty sand in order to analyze the strength and deformation characteristics of the improved soil. The stress-strain relations obtained from tiaxial tests were analyzed and the effect of coarse particles and fine particles on the strength and deformation of the specimen were also analyzed. The test results show that with more coarse particles and under a higher confining pressure, a greater deviator stress is required to produce the same axial strain. The increase of coarse particles helps to enlarge the angle of internal friction and cohesion, while the increase of fine particles decreases the angle of internal friction and cohesion. Under low confining pressure, the soil specimens with more coarse particles exhibit evident shear dilation. Under high confining pressure, the soil specimens produce a greater volume strain. Adding appropriate amount of gravel into the silt soil can increase its strength and restrain its deformation, but excessive amount of gravel may produce too much volume deformation.