Spatial Mechanic Effect Study During Construction Process Of Big-Span Highway Tunnel

With the rapid development of the state highway construction, it becomes more and more important for the study of stability of peripheral surrounding rock and its forced condition of the structure during construction of railway or highway tunnels, especially of those long or extra-long tunnels.Associated with a project of the planned Xuefengshan Tunnel with 7.6 km long during the construction of Shaoyang to Huaihua Expressway in Hunan province of Shanghai to Ruili National Trunk Highway, this paper firstly makes an introduction of the frequently-used analysis & computation methods for tunnel supporting structure.Then, based on the analysis of the basic theory about the interaction mechanism of surrounding rock and support structure, a spatial computation model is made, a coupling numerical computation method with 3-D elastic-plastic finite element and infinite element is proposed, and a comprehensive analysis has been made to the effects of the overall stability and safety of the surrounding rocks of different characteristics, different classes and under different construction methods. And thus the problem of 3-D infinite region to which applying the general finite can't do has been resolved. By adopting 3-D coupling method, the efficiency and maturity of FEM in analyzing the nonlinear, and the accuracy and simplicity of IFEM in dealing with the infinite region and half-infinite region are bringing into play fully. Thus a new way for stability analysis of the surrounding rocks during tunnel construction is opened up.Besides, based on the theoretical study, a corresponding coupling program with 3-D elastic-plastic finite element and infinite element is developed. According to the above contents, the effects of stability and safety of the surrounding rocks of different characteristics, different classes and under different construction methods are analyzed, the good and bad about different construction methods under the condition of the same kind of surrounding rock are compared, and some useful conclusions are drawn. These study results can offer scientific grounds for choosing the optimum construction method in the construction of Xuefengshan tunnel and other engineering of the same kind under the different conditions of surrounding rock.