EXPERIMENTAL STUDY ON INFLUENCE OF PARTICLE BREAKAGE TO CRITICAL STATE OF CALCAREOUS SAND

The particle fragility of calcareous sand is an important property that causes its deformation and strength characteristics different from standard sand. Based on the critical state theory,this paper quantitatively reveals the evolution of the critical state line of calcareous sand with particle breakage through a series of experiments. The experiment is carried out in two different stages. In the first stage,the deformation characteristics and particle breakage characteristics of calcareous sand under different confining pressures(60~2000 kPa) are analyzed. In the second stage,the samples with different crushing rates produced from the first stage is reshaped,he second shearing under the confining pressure of 100~300 kPa is performed,then the crushing critical state line is acquired. The test results show that under low confining pressure(<300 kPa) both loose and dense sand show the strain softening and dilatancy characteristics. While under high confining pressure(>1 MPa),significant particle breakage causes continuous shear contraction. There is an obvious confining pressure threshold for particle breakage. For loose sand,there is basically no particle breakage when the confining pressure is less than 300 kPa. In the e-lg p' plane,the intercept Δe_Γ and the slope λ_c of the crushing critical state line decreases with the increase of B_r^*,so the particle breakage makes the critical state line move downward and rotate counterclockwise. While in the q-p' plane,the critical state points of calcareous sand fall on the same straight line,indicating that there is a unique critical state stress ratio M_cr and critical friction angle φ_cr.