Dynamic mechanical response and fracture mechanism of rock-like materials with concealed structural planes of different filling thicknesses

Abstract

Structural planes are the primary variables determining the stability of rock masses. Numerous non-penetrating structural planes exist in nature and are concealed inside the slopes or underground rock formations. The concealed structural planes (CSP) pose a possible hazard to the construction safety of rock mass engineering, particularly for the rock mass subjected to dynamic load. Using rock-like materials, intact specimens and specimens with CSP of varying filling thicknesses are constructed in order to examine the dynamic mechanical response and fracture mechanism of rock masses with CSP. Single impact experiments and cyclic impact experiments are carried out at various speeds using the Split Hopkinson Pressure Bar experimental system (SHPB). The results demonstrate that the specimens' peak stress is negatively correlated with the filling thickness, and that as the reflection coefficient increases and the transmission coefficient decreases, the filling thickness increases. Also, the energy dissipation rate of the specimens is positively correlated with the increase in thickness of filling at impact velocities of 3.7 m/s and 4.5 m/s, with the rate showing an increasing trend followed by a decreasing trend at impact velocities of 5.5 m/s and 6.5 m/s. The main surface and internal cracks of specimens can be categorized into seven types, which are combined into three failure modes. As the filling thickness increases, the failure mode changes from transverse tensile failure to combined tensile and shear failure to bi-directional tensile failure under combined transverse and axial tensile action. The crack propagation behavior and the fracture mechanism from the interior to the exterior of the CSP specimens are investigated using the impact test results, finite element model, and mechanical theory analysis, which can be used as a reference to reveal the destabilization process of the rock mass with CSP.