Investigation into Rock Breakage with Expansive Cement Under Biaxial Confinement

While drilling and blasting with explosives is widely used for rock fragmentation in mining and civil engineering, its use is associated with rigorous safety and environmental constraints as blasting creates toxic fumes, vibrations and dust. In recent years, there has been a growing interest in transitioning from blasting with explosives to rock fragmentation without explosives. In this study, the potential of expansive cement (EC), aka soundless chemical demolition agent (SCDA), as an alternative to explosives to break hard rock under confinement is explored through a comprehensive experimental and numerical modelling study. To do so, two large-scale tests have been designed and carried out on 1 m x 1 m x 0.25 m panels made from high-strength concrete and subjected to planar, biaxial loading conditions. Such test configuration is designed to mimic a mining front subjected to biaxial stresses. Different EC drill hole patterns were tested and compared. The fragmentation behaviour due to EC was first examined with five particle flow code (PFC2D) models simulating different EC drill hole patterns. Two panel designs were retained for the large-scale experiment. It is found that rock breakage with EC under confinement is feasible and promising, especially when the optimized drill pattern from numerical modelling is adopted. It is demonstrated that discrete element modeling with PFC2D can be used effectively to design and optimize the EC drill hole pattern under biaxial confinement. The findings of this study could set the stage for numerous future applications of EC for rock fragmentation of subsurface hard rock excavations such as shafts, tunnels, and mine openings.