Field Experimental Study on Mechanical Characteristics of Primary Supporting in Weak Surrounding Rock Tunnel

Since the poor self-stability of weak surrounding rock when applied the full-face excavation in a tunnel construction, a large surrounding rock deformation are tended to occur, which causes a big security risk. Under the engineering background of gaojiaping tunnel of zheng-wan high-speed railway, the stress of surrounding rock, steel frame, initial shotcrete stress, bolt axial force and extrusion deformation of working face of the tunnel are monitored and analyzed respectively. The results show that the surrounding rock stress, steel frame stress and initial shotcrete stress of the tunnel are significantly affected by surrounding rock lithology and construction disturbance. The plastic zone of surrounding rock can be preliminarily determined as 3m according to the peak value of bolt axial force. The extrusion deformation of the tunnel working face shows that the surrounding rock integrity of the test section is good. The experimental study is helpful to collect the deformation of weak rock mass and provide reference for establishing scientific and reasonable support system.