Numerical simulation of blasting at tunnel contour hole in jointe rock mass

Abstract

The orientation and the spacing of discontinuity affect a failure mechanism of blasting, and they will cause a severe over-break. Such an over-break causes increasing the construction time and cost. So, it is necessary the study to clarify failure mechanism of blasting by orientation and the spacing of discontinuity. In this study, using PFC2D(Particle Flow Code 2Dimension), which was developed by Itasca Ltd., blasting at tunnel contour holes is simulated. To find out affection by the joint orientation it is set an analysis model having the angle of discontinuity the 0, 10, 20, 30, 45, 60, 90 degree. When the angle of discontinuity is under the 45 degree, the rock mass does not break out along new cracks but break out along the joint. When the angle is over 45 degree, the affection of discontinuity on blasting is decreased but failure surface is very rough. In order to find out the affection of joint spacing the analysis model is set joint spacing having 100, 200, 300 mm. As joint spacing is decreased the failure surface is very rough. When the rock mass have 3 joint set, the analysis model is set that the space of blast hole is 500, 600, 700 mm. From the result, the best blast hole spacing is 600 mm. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.