The Effect of Drainage Conditions on the Static Shear Characteristics of Calcareous Silt

Facing the global challenge of sea-level rise, the stability of land reclamation engineering is severely threatened by the weak calcareous silt interlayers formed during its construction process. This study investigated the mechanical behavior and particle breakage characteristics of calcareous silt through consolidated drained (CD) and undrained (CU) triaxial shear tests on specimens with varying initial dry densities, examining the effects of effective confining pressure and drainage conditions. Results showed that drained conditions induced strain-softening, which was enhanced by increasing effective confining pressure and initial dry density. Undrained behavior transitioned from softening to hardening with increased initial dry density. Although initial dry density affected the undrained stress path shape, both drainage conditions and initial dry density had a negligible influence on the critical state line. Particle breakage increased linearly with confining pressure in both drained and undrained shear tests, but was significantly greater under drained conditions. An empirical formula was established that relates particle breakage to confining pressure, mean effective stress and initial dry density, providing a theoretical basis for constitutive modeling and a practical tool for engineering applications.