Numerical Investigation on Rock‐Fracturing Mechanism by Using Splitter under Hole Assistance

Abstract

In this work, a numerical model of rock breaking under hole assistance was established based on the finite element method (FEM) coupling with smoothed particle hydrodynamics (SPH) to reveal rock-breaking mechanisms and analyze the reasons for crack formation and propagation under hole assistance. In addition, the numerical model was verified by experiment with and without a hole, and the simulation results are basically consistent with the experimental results in rock breaking. During the process of rock fracturing, the hydraulic splitter was first inserted into the predrilling hole, and then the wedges were pushed into the rock under the action of the hydraulic pressure. In this process, the splitter wedge was separated from the two sides, and the transverse bursting force was transmitted to the rock. Finally, the main fracture formed and the rock mass broke due to the bursting force. The results show that the cracks propagate along the approximately straight lines OO1 (the distance between the auxiliary holes and the left predrilled fracturing hole) and OO2 (the distance between the auxiliary holes and the right predrilled fracturing hole) before extending to the auxiliary hole which is unlike the crack propagation in rock without auxiliary holes, and the crack propagating direction gradually approaches horizontally and is vertical to the side after passing through the auxiliary holes. Moreover, when the auxiliary holes are located at the prefabricated angles α = 40° and 45°, the crack propagation can be well induced and the cracks pass through the auxiliary holes. However, at α = 50°, the auxiliary holes can no longer well induce the crack propagation in the process of rock breaking; however, the fracturing pressure is still less than that with no auxiliary holes, indicating that the auxiliary holes play a positive role in guiding rock breaking.

Utilizing numerical simulation to determine the reasonable parameters for the design of hydraulic rock-splitting head

“…The external dimensions of the wedge wing, and the wedge wing opening, depend on the hole. The mechanism for separating rock from boreholes is presented in [10]. In case the wedge wing sizes do not match the hole, it will affect working efficiency and reduce productivity.…”

“…where P (N) is the hydraulic cylinder pushing force, and N(N) is the rock splitting force. When the rock-fracturing mechanism using a hydraulic splitter under hole assistance, the rock splitting force can be calculated according to [10]. Formula (2) provides the relationship between the pushing force and the parameters of the wedge and wedge wing.…”

“…The foundational principles of calculations related to rock or concrete, mechanical design, and hydraulic transmission have been presented in [10][11][12][13][14][15]. In [10] a theoretical analysis of rock breaking containing hole is made, and then a numerical model of rock breaking under hole assistance is established. The rock-breaking mechanism is explained, including the reasons for crack formation, crack initiation, and propagation.…”

Numerical and Preliminary In Situ Investigation on Roadway Excavation Using Static Expansion Mechanical Fracturing

“…The work process of mechanical fracturing using a radial splitter starts a hole drilling, then the pump station provides high-pressure oil to the splitting bar through hydraulic oil pipelines to push the wedge block to move downward, and then the wedge block drives the wedge feathers to expand. In this process, the axial thrust is converted into the radial splitting force for the borehole wall [21]. When the splitting force is large enough, the rock will be fractured toward the side of the free surface.…”

Effect of charge coefficient on directional fracture of slotted charge

“…Yang et al (2014) investigated the dynamic stress intensity factor and crack tip propagation mode in dynamic caustic tests. Li et al (2019) studied the fracture characteristics of the cracks surrounding the bunch holes and analyzed the mechanism of crack initiation for defects in columns and ends. Based on computer tomography, Wang et al (2020) studied the propagation of shock waves, the damage characteristics of rock, and the dynamic fracture features of crack following explosion under coupled charge conditions.…”