Effects of Calcareous Fine Content on the Shear Characteristics of Calcareous Sand by Consolidated Undrained Triaxial Tests

The rich internal pore structure of calcareous sand allows fine particles and sand particles in the foundation to mix easily with each other during hydraulic transport during hydraulic filling and site leveling in later construction. The addition of fine particles can change the particle composition of calcareous sand， thereby affecting its mechanical properties. To analyze the influence of calcareous fine content on the static characteristics of calcareous sand， multiple sets of consolidated undrained triaxial tests were conducted under varied confining pressures on calcareous fine-sand mixtures with fine contents of 0%， 10%， 40%， 70%， and 100%. Changes in shear strength and pore pressure were investigated， and the impact of calcareous fine content on the breakage of calcareous sand particles was analyzed. The experimental results showed that as the fine content increased， the peak stresses of the calcareous fine-sand mixtures first decreased and then increased， while the peak pore pressures and peak internal friction angles first increased and then decreased. In this experiment， the turning points of these changes all occurred in the mixture samples with a fine content of 10%. As the confining pressure increased， the peak internal friction angles of the calcareous fine-sand mixtures decreased， and the relative breakage index increased. In addition， the relative particle breakage index of calcareous sand showed a strong linear relationship with both confining pressure and fine content. Based on the results of this study， the relative particle breakage index of calcareous sand can be expressed by a polynomial function of confining stress and fine content.