Study on Bolt Pre-tension Control in Underground Mine

The pre-stress is an important parameter of the bolt support and would have an important influence to the mine roadway support effect.The paper analyz ed the bolt pre-stress affected to the mine roadway support effect and the relevant relationship between the bolt pre-tightening torque and the pre-tension.According to t he conventional pre-tightening tools of the bolting operation in the present underground coal mines, the paper had a comparison on the advantage and disadvantage of each operation tools. From the technology, material and operational tools, the measures to control the bolt pre-tension in underground mine was provided.The rational s cope of the bolt pre-tightening torque was provided . As for the high strength bolt and the powerful bolt, the pre-tightening torque of the bolt would not be the higher the b etter, but shall have a rational scope of the pre-tightening torque. The underground site test measured data showed that as for the traditional high strength bolt, the pre-t ightening torque of the bolt shall be at 300 N.m and generally shall not be over 500 N.m.As for the powerful bolt, the pre-tightening torque of the bolt shall be at 400 N. m and generally shall not be over 550 N.m.Otherwise the bolt would be easy to be deformed and failed.With the underground mine cases, a test of the bolt pre-tension control was conducted and the bolt broken phenomenon was basically eliminated with excellent effect.