Investigation of shear behavior of notched bedding rock containing welded interface between hard and soft layers; an acoustic emission-based approach

Abstract

The present work investigates the impacts of layer number, ratios of layer, brittleness of layer, layer angle, and length of notch on the shear failure of bedding rock with a welded interface, using experimental punch test and numerical modeling. The study also analyzed the acoustic emission (AE) events throughout the entire process, from initial shear stress applied to the notched bedding layer to final rock bridge failure. Rectangular samples with varying numbers of soft and hard layers were prepared. The ratio of soft gypsum thickness to total sample thickness in the one soft layered model, one hard layered model, two-layered model, three-layered model with soft interlayer, and four-layered model was 1, 0, 0.5, 0.33, and 0.5, respectively. Each model consisted of two vertical non-persistent edge notches in one direction, with notch lengths of 20, 40, and 60 mm. All layers had a horizontal configuration in the experimental test (layer angle 90°), while angle of bedding layers varied from 0° to 90° with increments of 15°. The considered models were investigated using punch shear tests. The results indicate that a tensile crack was initiated at the tip of the notch, propagating parallel to the shear loading axis until coalescence with the model boundary. Both peak shear strength and shear stiffness decreased as layer angles increased in models consisting of two and four layers. The mechanical properties of the three-layered model improved with increasing layer angles due to the increased presence of the hard gypsum layer in the shear failure surface. Increasing the number of layers resulted in an increased number of major AE hits, while increasing the notch length led to a drop in the number of observed AE hits. Moreover, the number of major AE hits was higher in hard ductile gypsum than in soft brittle gypsum. The failure mechanism was consistent between numerical simulation and experimental testing.