Abstract：With the development of expressway tunnel，its stability is becoming the key problem for design and construction. According to surrounding rock characters of the Gonghe tunnel along Chongqing—Changsha road，model tests of unreinforced tunnel and bolt-reinforced tunnel are conducted on triaxial testing machine. Based on the model test，the complete failure course of surrounding rock is found. The strain gauge is used to record the strain of different parts of the surrounding rock，and the variability of the stress of surrounding rock under different conditions is analyzed. The following conclusions can be drawn. (1) The radial and the tangential stresses increase with the increase of load. (2) The radial stress increases with the increase of the distance from tunnel wall. (3) There is a stress concentration of the tangential stress on the tunnel wall，and the tangential stress decreases with the increase of the distance from the tunnel wall. (4) The radial and the tangential stresses of surrounding rock after reinforcement are higher than those before reinforcement. The bolt improves the stability of the surrounding rock. The reinforcement effect of the long bolt is better than that of the short bolt.
