Delay failure and fast fracturing of notched bedding rock under shear test condition: physical test and discrete element simulation

Abstract

This research investigates the impact of the brittleness of bedding, bedding angel, and the notch length on the delayed failure and rapid fracturing of notched bedding rock under shear conditions subjected to punch tests. Also, this paper analyzed the acoustic emission events throughout the entire process of rock bridge failure. For this purpose, rectangular two layered samples containing both hard- and soft-rock layers were employed. Each model included two vertical edge notches in a single direction, with notch lengths of 20, 40, and 60 mm. The bedding layers were varied from 90° to − 75° with increments of 15°. The results demonstrate that smooth cracks originated from the notch tip and propagated vertically until coalescing with the upper boundary of the model. The occurrence of acoustic emission in hard, ductile gypsum is considerably greater than that in soft, brittle gypsum. The shear stiffness of bedded rock is maximized when a higher percentage of shear surfaces is occupied by hard and ductile gypsum. Delay failure occurs in the hard, ductile layer, while fast fracturing occurs in the soft, brittle layer. In models with constant notch length, delay failure was occurred in models with a positive layer, whereas fast fracturing was observed in models with a negative layer angle. Additionally, delay failure changes to fast fracturing with an increase in the notch length. Failure patterns, shear stiffness, and shear strengths of the notched bedding models are similar to those of notched physical samples.