Abstract: In order to study the confining pressure effect and particle size effect of shear properties of calcareous sand, triaxial shear tests were carried out under different particle sizes, relative densities and confining pressures. The stress relative softening coefficient and dilatancy coefficient were introduced to quantitatively characterize the strain softening and dilatancy characteristics. The experimental results show that with the increase of confining pressure, the strain softening and dilatancy characteristics of calcareous sand samples with different particle sizes decrease gradually, and the confining pressure is semi-logarithmic linear with the relative stress softening coefficient and dilatancy coefficient. The strain softening and dilatancy characteristics of calcareous sand samples with different particle sizes disappear due to the existence of critical confining pressure of strength and critical confining pressure of volume variation. In the range of particle size 5-0.075 mm, confining pressure has a significant effect on softening and dilatancy characteristics of loose samples, but there is no significant correlation with particle size. For dense samples, the effect of confining pressure on softening characteristics of samples increases with decreasing particle size, while the effect on dilatancy characteristics of samples decreases. Under a low confining pressure (50 kPa), the breakage of 0.5-0.25 mm particle size group is the most significant.

Key words: calcareous sand, particle size effect, triaxial shear test