Effects of joint orientation in tunneling

Abstract

This research is focused on the effects of joint orientation with respect to the direction of tunnel axis. It is expected that the stability of surrounding rock is affected by the strike and dip of the joints and the direction of the tunnel axis, whether it is with the dip or against dip etc. similarly the spacing of joints will also affect the stability. The orientation of joints in different directions can form blocks liable to fall. The objective of this research project is to determine the degree of influence of joints' strike and dip orientation in tunneling. Field works related to this project was carried out at the Bogala Graphite Lanka Ltd. Tunnel mapping and other observations related to the project were made at 489.6 m level in Bogala mine. Models were made with joint spacing of 15 mm with two joint sets (joint sets parallel to tunnel axis and joint sets perpendicular to tunnel axis). Tunnels were created with 90 mm diameter with dip angles of joints are 0°, 30°, 60°, and 90°. The tunnels models are loaded using UCS machine and observed the behavior of rock mass around the tunnels during loading. From the results the most preferable dip angle for the joint strike perpendicular to the tunnel axis would be the 90° and for the joint strike parallel to the tunnel axis would be 0°.