Physics of Strain Burst in Hard Rock – Fracture characteristics and influences of the stiffness of the host rock mass

Abstract

Rock burst is a phenomenon in which rock disintegrates, accompanied by the ejection of debris. Strain burst is a type of rock burst. It is directly associated with stress concentration after rock excavation. Overstressed rock suddenly loses its integrity and broken rock pieces are ejected into the open space. Efforts have been made in the field observations, monitoring, and engineering control measures of strain bursts. However, little effort has been made on understanding the physics of strain bursts to date. Two prerequisites for strain bursts are stress concentration to fracture rock and excessive energy to eject the fractured rock. This work is focused on these two aspects to understand the physics of strain bursts in underground excavations, which relates to the relationships of strain bursts with mineralogy, petrology, microcracking and energy transfer during strain burst events. This work is based on microscopic observations of the cracks generated during the progressive failure of two different types of rocks, nano-indentation tests of the constituent minerals of rocks during failure, laboratory rock specimen bursting tests and strain burst numerical modeling using the finite difference code FLAC3D. This work reveals the fracturing patterns of rock before and after a burst and the energy conversion during a strain burst. It also reveals the effects of the stiffness of the surrounding rock mass on the intensity of strain bursts.