Improving blast-induced tunnel profile under different in-situ stresses

Abstract

Contour blasting techniques with pre-cutting areas are deemed as promising methods to improve the contour quality of tunnel with high in-situ stress. However, their performance under different in-situ stresses has not been well studied. In this paper, the performance of two typical contour blasting techniques, i. e., smooth blasting (SB) and pre-splitting blasting (PB) with pre-cutting (PC) areas (namely PCSB and PCPB) under different ground stress conditions is investigated by the road tunnel numerical model after calibration. The results show that under the coupled charge and 50 MPa in-situ stress, PCSB can form a better tunnel contour than PCPB. In addition, the performance of two techniques is investigated with different decoupled charge coefficients and in-situ stresses. It can be found that the contour quality under the PCSB and PCPB both gradually improves with increased in-situ stresses from 30 to 50 MPa. Moreover, adjusting decoupled charge coefficients of peripheral boreholes is feasible for the PCPB to form effective tunnel contour under different in-situ stresses. However, it is more appropriate to adjust decoupled charge coefficients of all boreholes for the PCSB to form eligible tunnel contours under different in-situ stresses. Empirical formulae are finally given to provide design guides of PCSB and PCPB to excavate different in-situ stresses of rock mass used in this paper.

Keywords

in-situ stress / smooth blasting / pre-splitting blasting / tunnel contour quality / decoupled charge coefficient

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