Dilatancy of coarse-grained soil in large-scale triaxial tests study

Dilatancy is a basic behavior of soils which is closely related to strength and deformation behaviors of soils and makes soils significantly different from normal elastic materials. Four groups of large-scale triaxial tests were conducted to investigate the influence of dilatancy on strength and deformation behaviors of coarse-grained soils at different initial densities. The test results show that: (1) The stress-strain curve shows softening behavior if volumetric strain rate (the ratio of volumetric strain increment to axial strain increment, assume positive for volumetric strain and axial strain under compressed condition) firstly decreases from a positive value to a negative value and then increases but still smaller than zero; the dilatancy and strength of the soil reach maximum at the minimum value of the ratio, otherwise the stress-strain curve behaves as hardening behavior if the ratio of volumetric strain increment to axial strain increment decreases monotonously from a positive value but always larger than zero. (2) The variation trend of volumetric strain depends on dilatancy and compressibility of soils; the volumetric strain is firstly compressive and then dilatant and stress-strain curve behaves as stress softening form if dilatancy rate (the negative of the ratio of volumetric strain increment caused by shear stress to axial strain increment) is larger than compression rate (the ratio of volumetric strain increment caused by compression stress to axial strain increment) in the late shear stage; otherwise the volumetric strain is always compressive and the stress-strain curve behaves as hardening behavior for the condition that dilatancy rate is smaller than compression rate in the whole shear stage. It is of great importance to know the dilatancy of coarse-grained soils for insight into the strength and deformation behaviors of coarse-grained soils.