Effect of inter-layer thickness on dynamic mechanical properties of rock mass combined with hard and soft media

In order to explore the influence of interlayer thickness on the dynamic mechanical properties of the rock mass composed of soft and hard media, taking sandstone and granite as the soft and hard rock matrix, the energy evolution and loss laws of the rock mass composed of soft and hard media under different interlayer thicknesses (0 mm, 5 mm, 10 mm, 15 mm) were studied by using the split Hopkinson pressure bar device, and the energy driving mechanism of its failure was explored. The discrete lattice spring method (DLSM) was used to simulate the crack growth, stress time and damage strain evolution of rock mass with different interlayer thicknesses. The results show that with the increase of interlayer thickness, the resistance of interlayer to the crack growth and development of rock mass is gradually enhanced, and the energy consumption is gradually increased. The energy driving mechanism for the failure of the composite rock mass containing interlayers of soft and hard media is: under the impact load, the elastic energy in soft rock, hard rock and interlayers increases continuously, and the elastic energy stored in the interlayers of the composite rock mass first reaches its bearing capacity limit, and the interlayers are rapidly destroyed. After the failure of the interlayer, the stored energy is released instantaneously and transferred to the soft rock and hard rock. Cracks begin to appear in the soft rock. Under the combined action of the energy released by the interlayer and the energy stored in the rock itself, the soft rock will have cracks and produce a little damage. The failure of interbedded rock mass starts at the interbedded cementation surface. With the increase of the interbedded thickness, only one side of the sandstone near the cementation surface is partially fractured. The growth rate of rock mass stress is inversely proportional to the interlayer thickness. The rate of damage degree increasing with strain of rock mass with low interlayer thickness (0 mm, 5 mm) is relatively constant compared with that of rock mass with other interlayer thickness. The damage degree of rock mass with high interlayer thickness (10 mm, 15 mm) increases rapidly with the strain in the late stage of crack growth.