Study on the Mechanical and Mesoscopic Properties of Rockfill Under Various Confining Pressures

To investigate the mechanical response characteristics of damming rockfill materials under different confining pressure conditions, this study integrates laboratory triaxial compression tests and PFC^2D numerical simulations to systematically analyze their deformation evolution and failure mechanisms from both macroscopic and microscopic perspectives. Laboratory triaxial test results demonstrate that as the confining pressure increases, the peak deviatoric stress rises significantly, with the shear strength of specimens increasing from 769.43 kPa to 2140.98 kPa. Under low confining pressure, rockfill exhibits pronounced dilative behavior, whereas at high confining pressure, it transitions to contractive behavior. Additionally, particle breakage intensifies with increasing confinement, with the breakage rate rising from 4.25% to 8.33%. This particle fragmentation alters the granular skeleton structure, thereby affecting the overall mechanical properties and leading to a reduction in shear strength. Numerical simulations further reveal the micromechanical mechanisms governing rockfill behavior. The simulation results show a shear strength increase from 572.39 kPa to 2059.26 kPa, exhibiting a trend consistent with experimental findings. The shear failure mode manifests as a characteristic "X-shaped" shear band distribution, while at high confining pressures, shear fracture propagation is effectively inhibited, enhancing the overall structural stability. Furthermore, increasing confining pressure promotes denser interparticle contacts, with contact numbers increasing from 16,140 to 18,932 and the maximum contact force rising from 12.19 kN to 59.83 kN. The quantity and frequency of both strong and weak force chains also increase significantly, further influencing the mechanical response of the material. These findings provide deeper insights into the mechanical behavior of rockfill materials under varying confining pressures and offer theoretical guidance and engineering references for dam stability assessment and construction optimization.