Crack growth properties and AE phenomena in notched hard/soft layered rock under punch shear test; experimental test and numerical simulation

Facing layered rocks is common in various mining geotechnical and tunnel engineering projects. These layers vary in thickness and are separated by bedding planes, which can either be cemented together or distinct from each other. Totally, these components form the entirety of the rock mass. The study examined how the thicknesses of hard and soft rock layers, layer number, layer angle, and notch length affect the shear failure mechanism and acoustic emission (AE) events of notched bedding rock. For this purpose, experimental punch tests and numerical simulations with normal stress of 2 MPa were used. They prepared samples including one soft layer, one hard layer, a two-layered model with hard and soft rock layers, three layered model with a soft interlayer, and a four-layered model with two hard and two soft rock layers. Each model had two edge notches in one direction. The shear behavior of notched hard and soft rock layers was subsequently simulated using particle flow code (PFC). The layer numbers were the same as the physical samples, with the bedding layer angles changing from 0° to 90° in increments of 15° in numerical simulation. The results showed that increasing the notch length reduced the shear strength and stiffness. The major AE hit number was higher in hard ductile gypsum than in soft brittle gypsum. In the soft brittle model, the final failure occurred immediately after crack initiation, while delayed failure occurred in the hard ductile model.