Mechanical response and cracking behavior of fractured rock-mortar composites under coupling effects of fracture properties and interface strength

The mechanical behavior of rock-mortar composite (RMC) systems in tunnel engineering is of great importance for maintaining the structure stability and safety. However, the low-strength bonding of RMC results in the reduction of interface strength, accompanied by the formation of open interface fracture, which greatly affects the stability and safety of composite system. In this work, the coupling effects of fracture properties and interface strength on the mechanical response and cracking mechanism of RMCs with an open interface fracture under radial loading is studied via the finite-discrete element method (FDEM), which are validated through experimental tests. Firstly, the numerical models of RMC are built according to the laboratory sample preparation, and the input parameters of sandstone and mortar in FDEM are calibrated with Brazilian splitting tests of intact samples. Secondly, the co-effects of open interface fracture orientation ( a ) and length ( L ) on the mechanical behavior, acoustic emission (AE) signals, crack deflection angle and failure patterns are studied. Results indicate that the peak load increases as a increases but decreases as L increases. Meanwhile, the cracks are initiated at the fracture tips and then deflects to the top and bottom loading points when a ≤ 45°, and the deflection angle increases with an increasing a . Finally, the reduction factor of interface strength ( η ) on cracking mechanism is discussed. The peak load increases linearly as η increases when a = 0°, but changes little with other a . Besides, shear cracks are generated at the interface with η of 0.2 and a of 15°, 30° and 45°, while tensile damage is predominant in other cases. The findings can offer theoretical support for the stability analysis and design of tunnel involving RMC structures.