Mechanical properties of rock under coupled static-dynamic loads

Rock drilling machine, INSTRON testing system, and SHPB device are updated to investigate the characteristics of rocks at great depth, with high loads from overburden, tectonic stresses and dynamic impacts due to blasting and boring. It is verified that these testing systems can be used to study the mechanical properties of rock material under coupled static and dynamic loading condition and give useful guidance for the deep mining and underground cavern excavation. Various tests to determine the rock strength, fragmentation behavior, and energy absorption were conducted using the updated testing systems. It is shown that under coupled static-dynamic loads, if the axial prestress is lower than its elastic limit, the rock strength is higher than the individual static or dynamic strength. At the same axial prestress, rock strength under coupled loads rises with the increasing strain rates. Under coupled static and dynamic loads, rock is observed to fail with tensile mode. While shear failure may exist if axial prestress is high enough. In addition, it is shown that the percentage of small particles increases with the increasing axial prestress and impact load based on the analysis of the particle-size distribution of fragments. It is also suggested that the energy absorption ratio of a specimen varies with coupled loads, and the maximum energy absorption ratio for a rock can be obtained with an appropriate combination of static and dynamic loads.