Overlying Rock Thickness Calculation of Roadway with Pressure Based on Unified Strength Theory

The elasto-plastic analysis for the stress of surrounding rock of roadway with pressure was carried out based on unified strength theory.By controlling the radius of plastic zone,the formula of the minimum overlying rock thickness was deduced.The effect of the intermediate principal stress on the material strength and the effect of strength difference in tension and compression were considered in the obtained formula.A series of overlying rock thicknesses could be obtained by defining the coefficient of intermediate principal stress.In practical engineering,the proper coefficient of intermediate principal stress could be obtained according to the experiment results of rock,and the minimum overlying rock thickness could be reasonably determined,furthermore,the roadway could be designed reasonably.The analytical results show that the formula considers the strength difference in tension and compression and intermediate principal stress,and the formula can be degenerated into the formula under other surrounding rock conditions or other strength theories.It has a good practicality.