Numerical Analysis Of The Stability For The Surrounding Rock During Dynamic Construction Process Of Large-span Tunnel

With the rapid development of the state high grade construction, there are more and more highway tunnels, especially large-span highway tunnels. In the course of the highway tunnel's construction, the stress in rock mass will redistribute around grotto, When this kind stress exceeds surrounding rock's ultimate strength, surrounding rock will lose its stability and destruct. Consequently, it becomes increasingly important for the study of stability of surrounding rock and its forced condition of the structure during construction of highway tunnels.Longtoushan tunnel in Guangdong province is the largest one cave and 4-lane highway tunnel in china, which is bidirectional and detached. The biggest excavated width in construction is 21.1m, its biggest clear height is 13.2m. Associated with the project of Longtoushan tunnels, sticking to the evaluation of surrounding rock's stability of large-span highway tunnels, in order to uphold surrounding rock's stability and direct highway tunnel's construction, with the combination of qualitative evaluation, quantitative evaluation, integrate and local evaluation, the paper studies the surrounding rock's stability of tunnels systematically. Firstly, the paper studies characteristic of mechanics and criterion of surrounding rock's stability for the large-span highway tunnels and confirms criterion of surrounding rock's stability. Secondly, starting with the engineering geological factors influencing surrounding rock's stability of tunnel, the paper carries on the analysis and discussion about deformation and destruction mechanism to surrounding rock, the author puts forward the strength of rock, growth degree of discontinuity, characteristic of soft discontinuity are primary factors influencing surrounding rock's stability in Longtoushan tunnel. Finally, based on the analysis of the basic theory about the interaction mechanism of surrounding rock and support structure in construction, a spatial computation model is made, a numerical computation method with 3-D elastic-plastic finite element is proposed to analyze stability and safety of the III surrounding rock in construction, through analyzing the distributing law of displacement, stress and strain in rock mass followed with tunnel's construction, the author gets some beneficial conclusions,which is of guiding meaning for evaluation of stability and security in surrounding rock during construction of large-span highway tunnels.