Appropriate Dynamically-Reinforced Supporting Time Determination in Relation to the Time Effect of Stress Field Evolution: A Case Study on the Deep Soft-Rock Roadway in China

In order to choose the appropriate time for the dynamic reinforcement, the time effect of stress field evolution of the surrounding rock was first analyzed in this study. Then the deep soft rock roadway in Xinhu Coal Mine, China was taken as a typical example with regard to how the rheology-affected stress field of the surrounding rock evolved. The calculation algorithm of stress field evolution was given together with the corresponding program developed. Calculation results showed that the peak point of the surrounding rock in the early phase moved faster, where the turn appeared on the 60th day when the peak point lied 6.96 m away from the center of the roadway. Then the peak point moved at a slower pace, and finally, on the 124.8th day, the stress peak point was basically stabilized 7.21 m away from the center. In this way, the appropriate dynamically-reinforced supporting time of the No. 2 North rail-crosscut in Xinhu Mine was determined as 60 days after the primary support. In addition, a dynamic reinforcement technical plan was developed. The primary supporting system was bolt + W-shaped strip + diamond mesh + shallow hole grouting bolt + cable + shotcrete, and the reinforcement support system was bolt + M4 strip + diamond mesh + grouting cable. In-situ observation showed that both the maximum deformation and its maximum velocity in the roof and both walls of the roadway were small. The results indicated that both the reinforced supporting time and the parameters are appropriate.