Model Test on Effect of Dynamic Pressure Arch of Tunnel in Soft Broken Surrounding Rock

In order to explore whether arch effect of surrounding rock develops dynamically with the progressive failure of tunnel,taking soft broken surrounding rock as test object,using blanc fixe,river sand and cleanser essence to simulate the material of surrounding rock,full-face cutand-cover tunnel method was used on test platform by self-design to measure and record the change of surrounding rock stress from tunnel excavation to the end of the collapse.The results show that with the tunnel excavation,the horizontal stress is in reverse proportion to the vertical stress on haunch.Due to the brittle failure,both the radial stress and horizontal stress of surrounding rock at the position nearest to the tunnel are decreased.Due to the plastic failure,the radial stress of surrounding rock near the tunnel is increased and the horizontal stress is decreased.At the relatively distant area,the radial stress is decreased and the horizontal stress is increased.The plastic zone would develop to the inner of surrounding rock if the tunnel is not supported in time after tunnel excavation.According to the position change of horizontal stressvalue in tunnel vault and vertical peak stress value on haunch,it is confirmed that arch effect develops dynamically with the tunnel collapse.