Numerical investigation of an improved deep-hole presplitting method based on notched blasting for deep-buried high sidewall structures

Abstract

Under high stress conditions, the local stress concentration in the high sidewall structure of a deeply buried powerhouse is obvious, and sidewall presplitting formation is significantly affected. For deep hole presplitting blasting (DHPB) widely used in underground powerhouse, the non-uniform stress characteristics of DHPB were first revealed through three-dimension (3D) numerical simulation, and three crack formation modes were subsequently classified. Afterwards, an improved excavation method of notched blasting fusion to DHPB was proposed to reduce the difficulty and inhomogeneity of DHPB brought by complex stress environment. A single hole 3D model was used to confirm the stronger guiding effect of notched blasting on crack expansion when the maximum principal stress direction is different from its. And the feasibility of the improved presplitting method on high sidewalls is pointed out by 3D numerical simulation. The results show that, for DHPB, the stress concentration at sidewall foot induced by powerhouse excavation causes a gradual change in its stress environment, and the horizontal lateral pressure coefficient (Ratio of transverse to axial) decreases with hole depth basically, while there may be a principal stress direction dividing point with a coefficient of 1.0. The direction of crack formation near the top of presplitting holes tends to be lateral to the powerhouse, whereas that near the bottom of presplitting holes tends to be axial to the powerhouse. This effect is exacerbated further by continuous undercutting of the lower and middle parts, resulting in more uneven pre-cracking of DHPB. The improved excavation method based on notched blasting can ensure that the notched direction is the dominant crack expansion direction among both notch cutting and maximum principal stress direction, weaken the influence of uneven stress environment on the presplitting formation, and re-achieve the good crack formation between holes of DHPB.