The investigation of rock indentation simulation based on discrete element method

Abstract

Rock indentation is widely encountered in rock engineering, such as oil & gas drilling process. The rock indentation represents the fundamental process for mechanical rock breaking. Therefore, it is necessary to research the failure mechanism during the rock indentation process. For this purpose, the Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests are performed to calibrate the relations between micro-properties and macro-properties of the rock specimens. The rock indentation process and crack propagation with the effects of lateral pressure, hydraulic pressure, ledge, wedge angle and joint are researched by PFC2D in this paper. The results show that: with the indenter penetrating into rock, the sub-vertical crack is formed from the damaged zone and it will extend to bottom edge of the rock at last; the initiation and propagation of the sub-vertical crack is mostly driven by the tensile contact force. The development of sub-vertical crack and damaged zone are restrained with increasing lateral pressure, the lateral pressure increases led to an increase in the critical penetration depth and the size of the damaged zone decreases and its shape flattens with the lateral pressure increasing. On the contrary, the development of sub-vertical crack and damaged zone are promoted with increasing hydraulic pressure. With the wedge angle increases the size of crushed zone underneath the indenter increases, it promotes the formation of sub-vertical crack; larger wedge angle causes a larger indentation force. The existence of a ledge leads to crack initiation and propagation towards the free surface and the presence of the joint also promotes crack initiation and propagation towards the joint; when the crack propagates to the joint, the crack will no longer propagate towards the intact rock mass but along the joint.