Mechanism of explosive crack propagation under the coupling of high crustal stress field and explosion stress field

To clarify the crack propagation mechanism under the coupling of high ground stress field and explosion stress field in rock engineering blasting, this study quantitatively explores the influence of this coupling effect on rock crack propagation through theoretical analysis, laboratory experiments and numerical simulation. By analyzing the crack propagation process and fracture morphology in different confining pressure blasting model experiments, and synchronously simulating the dynamic process of explosion-induced cracks and comparing with experiments, the results show that the coupling of confining pressure and explosion stress field changes the elastic-plastic zone and stress distribution at the crack tip of rocks, as well as the crack propagation path and speed. Under unidirectional confining pressure, the same-direction confining pressure causes tensile stress concentration in the loading direction of the specimen, and the crack propagation length increases by up to 76.5 % compared to no confining pressure. In the vertical direction, compressive stress concentration occurs, and the crack propagation length decreases by up to 39.5 %. Under bidirectional equal confining pressure, compressive stress significantly inhibits crack propagation, and the crack lengths in the x and y directions decrease by 76.3 % and 52.9 % respectively compared to no confining pressure. Moreover, the crack propagation direction is more inclined to be consistent with the confining pressure stress field direction. The explosion stress wave incident in the positive direction induces type I cracks, and the oblique incidence forms type I + II composite cracks. Compared with no confining pressure, in the direction where confining pressure generates compressive stress, the peak stress intensity factor at the crack tip decreases by up to 74.3 %, and the effective stress decreases by up to 47.6 %. Confining pressure simultaneously enhances the compressive strength of rocks and the attenuation speed of stress waves, increasing the energy required for crack propagation. In the direction where confining pressure generates tensile stress, the crack propagation speed increases by 26.0 %, the effective stress increases by 36 %, and the energy required for crack propagation decreases. The crack propagation mechanism revealed by this study under the coupling effect provides theoretical basis and technical support for the design and construction of rock engineering blasting in mines.