Dynamic Response Characteristics and Damage Evolution of Multi-Layer Combined Coal and Rock Mass under Impact Loading

Abstract

The areas involved in coal and gas outbursts are composed of multi-layer coal and rock mass, in which external dynamic disturbance propagates in the form of stress waves; therefore, reflection, transmission and diffraction occur at the interfaces, resulting in dynamic effects such as reflected tension, convergence and superposition of stress and strain, and sudden changes of reflected and transmitted stress, which are the key factors leading to the outburst. Based on the Split Hopkinson Pressure Bar system, the dynamic time–history changes of stress, strain and strain rate of five-layer combined coal and rock mass were studied under impact loading. The results show that the time–history curves of stress and strain could be divided into five stages and that of strain rate three stages; the dynamic curves of the five stress–strain stages were significantly different between high-velocity and low-velocity impact. It was hypothesized that under high-speed impact loading, the mechanical anisotropy of combined coal and rock mass at the linear elastic stage tends to be isotropic. Based on ANSYS LS-DYNA, the damage evolution and failure process of five-layer combined coal and rock mass were simulated and analyzed under impact loading. It is concluded that the initial positions of damage of each layer were located at the circle center and its vicinity; radial cracks were mainly formed under low-speed impact loading, and circumferential cracks were mainly formed under high-speed impact loading. In the propagation and action of loading and unloading waves, the “weak layer” was damaged first by tensile stress and formed a free surface, and the subsequent loading waves were reflected on the free surface to form unloading waves and tensile stress, resulting in damage and spalling in multi-layer coal and rock mass.

Study on the Influencing Factors on the Effectiveness of Liquid Nitrogen Fracturing Technology

“…The study found that the ice wedge expansion of saturated water under low temperature conditions has the greatest impact on the destruction of coal and rock joint structure. This is because the pore water becomes ice during the freezing process of LN 2 , and the volume expansion, pore pressure increase, and the internal pore structure of the rock is destroyed, resulting in stress concentration and fracture propagation [30]. For dry and low water content coal, low temperature freezing mainly plays a role in weakening pore structure.…”

Durability Assessment Method of Hollow Thin-Walled Bridge Piers under Rockfall Impact Based on Damage Response Surface

“…The impact between the rockfall and HTWBP is achieved by the automatic surface-surface contact (*AUTO_CONTACT_SURFACE_TO_SURFACE). LS-DYNA software provides a variety of material models for concrete materials [18]. The most commonly constitutive models used to simulate concrete materials in engineering applications are as follows: MAT_111 (Johnson Holmquist concrete model), MAT_72R3 (concrete damage REL3 model), MAT_96 (concrete brittle damage model), MAT_159 (continuous surface cap model, or CSCM).…”

Durability Assessment Method of Hollow Thin-Walled Bridge Piers under Rockfall Impact Based on Damage Response Surface

“…LS-DYNA software provides a variety of material models for concrete materials [18]. The most commonly constitutive models used to simulate concrete materials in engineering applications are as follows: MAT_111 (Johnson Holmquist concrete model), MAT_72R3 (concrete damage REL3 model), MAT_96 (concrete brittle damage model), MAT_159 (continuous surface cap model, or CSCM).…”