Numerical study on the effect of in-situ stress on smoothwall blasting in deep tunnelling

Abstract

In the present study, a numerical model is first calibrated against the crack networks and pressure attenuation data in laboratory blasting test. Then, based on the calibrated numerical model, two-hole plane models are developed and used to perform a series of simulations of smoothwall blasting in deep tunnelling subjected to in-situ stress. The evolutions of rock fracture and excavation damage zone in the roof/floor and sidewalls under different far-field hydrostatic pressure and anisotropic in-situ stress conditions are numerically investigated. The findings in numerical modelling are also analytically interpreted with the stress distributions around the designed tunnel perimeter and perimeter borehole. The numerical and analytical results show that the variations of rock cracking and excavation damaged zone induced by smoothwall blasting with in-situ stress are mainly attributed to the high tangential compressive stress concentration around the remaining rock after inner primary blasts and the tensile stress acting on the wall of perimeter hole, which control the crack propagation and initiation respectively. At last, the implications of findings for practical smoothwall blasting in deep tunnelling are discussed.