Analysis Of Surrounding Rock Stability Of Soft Rock Tunnel And Study On Its Supports

In soft rock tunnel engineering, how to determine the stability of surrounding rock is key, difficult point during the period of designing and constructing. Accidents happen from time to time because of the variability of surrounding rock, which lead to the heavy losses of people's life and property. To study the deformation principle of surrounding rock have a practical significance in view of the variable characteristics of surrounding rock.Taking Zhangou tunnel with rank IV and rank V surrounding rock as an example, the characteristics and mechanism of deformation in the surrounding soft rock are analyzed. Meanwhile, the factors that influence the stability of surrounding rock are also analyzed. Based on the elastoplasticity theory, numerical model has been established in this paper with the FEM software of ANYSYS9.0 as a tool. The deformation principle of surrounding rock and the influence of burying depth on stability are also simulated under the same supports to find out the similarities and differences under different rank surrounding rock condition. Through analyzing and forecasting the deformation and stress state in surrounding rock and supports the stability of surrounding rock can be evaluated to optimize and consummate the tunneling procedure and supporting parameter. The conclusion is as follows:In the aspect of deformation, under the same burying depth the deformations of different rank surrounding rocks have the same tendency, but the biggest displacement distribution rule is different at the vault and soleplate. The displacement of rank V surrounding rock reduces more obviously after being supported than that of rank IV. In the aspect of stress distribution, under the same condition stress distribution in different rank surrounding rock basically obeys the same principle, however the rank V surrounding rock is more easily influenced and the stress zone is also slightly bigger than that of rank IV. Besides, the tension stress zone at vault and soleplate is more easily appearing and obviously higher than that of rank IV. In the aspect of plastic zone, the plastic zone in rank V surrounding rock is obviously larger than that of rank IV. When the rank of surrounding rock gets lower, the plastic zone will have a rapid expansion towards the vault. In the aspect of initial period supports, the maximum value of shearing force and bending moment appears at the same place under different rank surrounding rock. The maximum value of axle strength moves towards the vault when surrounding rock changes from rank IV to rank V. Also, the force exerted on initial supports increases when the rank of surrounding rock gets lower. In the aspect of burying depth, displacement, axle strength, bending moment and shearing force have an approximate relationship of linearity with the increasing burying depth. But the force exerted on initial supports increases more quickly in lower rank surrounding rocks than higher rank surrounding rocks.Finally, the modeling results have been used to compare with actual condition of the project, it proves to have a good effectiveness, which can be used to instruct the tunneling construction.