Abstract: The influence of stone size on the shear strength of gravel soil was investigated through large direct shear test on three groups of remolded gravel soil specimens of different stone sizes. The gravel soil in the slope of Daqianshiling Tunnel in the Tianshifu-Huanren railway was taken as research object. On this basis, the characteristics of grain size distribution of the gravel soil specimens were researched by using fractal theory. The fractal dimension of gravel soil with different stone sizes was obtained, and the relationship between shear strength parameters and fractal dimension was studied. Results indicate that when stone content is the same, shear strength and internal friction angle increase with stone size increasing; on the contrary, cohesion decreases along with the increase of stone size. With the increase of stone size, fractal dimension increases, and as fractal dimension gets bigger, the particle distribution is more uneven, and vice versa. There is a certain degree of correlation between shear strength parameters and fractal dimension. With the increase of fractal dimension, cohesion decreases whereas internal friction angle increases; cohesion and internal friction angle have approximately parabolic function relationship with particle fractal dimension.

Key words: gravel soil, large direct shear test, strength characteristics, stone size, fractal theory