Crack propagation patterns and energy evolution rules of coal within slotting disturbed zone under various lateral pressure coefficients

Abstract

Lateral pressure coefficient is an important parameter in geological engineering, and it influences significantly the damage zone around boreholes. In accordance with the fundamental principles of the Particle Flow Code (PFC), various models were established to investigate the crack propagation patterns and energy evolution rules of coal in disturbed zones of hydraulic slotting for various lateral pressure coefficients. Cracks around a slotted borehole propagate in the horizontal direction when the lateral pressure coefficient λ is less than 1, distribute uniformly when λ is equal to 1, and extend mostly in the vertical direction when λ is greater than 1. The total number of cracks increases linearly with λ. The variation in kinetic energy for coal failure was recorded; kinetic energy evolution observes a similar rule and its process can be divided into four stages, namely, the quick-release, rapid dissipation, drastic fluctuation, and stabilized stages. The peak value of the kinetic energy increases linearly with λ. The acoustic emission events distribute discretely when λ is small and uniformly when λ is equal to 1. The variation in acoustic emission events tends to increase sharply before decreasing when λ is greater than 1. The research findings are significant to the exploration of pressure relief mechanisms for hydraulic slotting from a microcosmic perspective.