Design Theory And Application Research On Full-face Pre-reinforcement Technology Of Soft And Weak Tunnel

In recent years, soft and weak rock located in complicated hydro geological conditions, often had been encountered when high railway tunnels were constructed. That relaxation zone comes into being close to tunnel face force rock mass and shotcrete support to deform with the characteristics of low strength, fractured joints, faults presenting granular structures and poor stability. The engineering disasters such as shotcrete support deformation invasion and tunnel collapse are very prone to appear once engineering measures and construction methods are not reasonable. The key to control the collapse is to stabilize rock mass. And the key to stabilize rock mass is to handle well the core soil ahead of tunnel face to be excavated ahead of tunnel face. However, NATM could be difficult to satisfy the current urgent need for tunnel construction because of complex construction procedures, seriously wasted materials, and slow duration. To this end, tunnel face pre-reinforcement technology was proposed base on tunnel construction technology theory and experiences at home and abroad, which was that bolt-cutting glass fibers along tunnel centerline to enhance strength of the core soil were used to reinforce the core soil to be excavated ahead of tunnel face and to control the deformation of the core soil. In this way, the space arch effect ahead of tunnel face can naturally play a role and ensure tunnel to realize full-face construction quickly and safely.Presently, relevant cases about tunnel face pre-reinforcement technology were seldom seen in the country, and also had no successful experience to follow. The process and failure mode of tunnel collapse are discussed firstly in this paper. And the mechanism of tunnel face pre-reinforcement technology is studied. On this base, the convergence-confinement method of tunnel face pre-reinforcement technology is studied, mainly including ground response curve, support characteristic curve, longitudinal deformation profile and extrusion deformation curve based on the stress release ratioλ. FLAC3D is used to study the mechanism of space arch effect and pipe roof and glass fiber blots influencing on pace arch effect. The basic technical parameters fit to the tunnel face pre-reinforcement technology of railway tunnel are obtained such as density (number), length, stiffness of reinforcements, overlapped length of reinforcements and so on. The results of theoretical and numerical analysis indicate that the theoretical plastic radius, the maximum horizontal displacement of tunnel face, failure mode of tunnel collapse basically agree with those of the numerical analysis. Then, the mechanical properties of bolts are studies in laboratory test, and the basic principles and methods of work face horizontal displacement are introduced in details. Monitoring design and results are used for evaluation of pre-reinforcement. Finally, the measured results in underpass of Xiamen compare with the theoretical and numerical ones. The problems and suggestions were pointed out when pre-reinforcement technologies were applied in Xiamen underpass.