Sensitivity Analysis On Selection Of Construction Method For Large Span Tunnel

There are many mountains in our country, so it will cause many tunnels to build during the highway projects. At present, there isn't perfect underground structural theory to guide the design and construction of tunnel, so it is inevitable that the project accident occurs now and then.With the support of the dangerous project situation induced by the mutation of the class of surrounding rock in Liushan Tunnel of Hangzhou-Anhui highway project, with the numeric analysis software this paper mainly makes a study to the influence of the different excavation methods to the stability of the surrounding rock, considering different class of surrounding rock,the span length of tunnel and the lateral pressure coefficient.The conclusions are:①Through establishing and analyzing 3-D FEM of the unomal geology section in Liushan Tunnel, the conclusion shows that bench excavation is better than full section excavation under the weak surrounding rock condition.②The whole procedural analog result for different excavation method shows that, the time when the stress field and displace field are changed greatly, is after the arch crown loses supporting of the rock pillar completely. If the arch crown loses supporting, the upper load will be supported by the arch formed by excavation, at the same time the stress alteration of the pressure arch will lead to the stress alteration of the surrounding rock nearby the working face, and the stress concentration will happen nearby the arch springing and arch crown too.③Considering the different classes of surrounding rock, the analog result for different excavation methods shows that, with the surrounding rock becoming bad, the influence on sensitivity of excavation methods selection becomes great. As a result of it, the worse the surrounding rock is, the more important to choose a proper construction method.④Considering the different span length of tunnel, the analog result for different excavation methods shows that, with the increase of the span length, the influence on sensitivity of excavation methods selection will become greater. Therefore, the more the span length is, the more important to choose a proper construction method.⑤Considering the different lateral pressure coefficient, the analog result for different excavation methods shows that, with the increase of the lateral pressure coefficient, the influence on sensitivity of excavation methods selection will become weaker. Therefore, the smaller the lateral pressure coefficient is the more important to choose a proper construction method.