Study On Mechanical Behavior Of Reconstruction And Extension For Typical Highway Tunnel

As the rapid development of economy puts forward higher requirements to the highway transportation capacity, nowdays many four-lane highway need renovation and expansion of the six-lane or even eight-lane, and the renovation of tunnel along which have become the key projiect. Though a practical research for Quanzhou-Xiamen Expressway Dai Mo Shan Tunnel expansion project, an analysis about the design and construction programs for four-lane expansion of the eight-lane which with typical significance was done, so as the effect of approaching excavation to the existing tunnel and the surrounding rock.Among all these plans for Dai Mo Shan Tunnel, to build a new tunnel and expand a existing one drives smoothly and flowly, spends a short duration and needs a moderate technical conditions. Through a research for practical situation, rationa rock conditions and forepolling parameters have been chosen. A three-dimensional finite difference model was built for construction analysis. It came to the influence in terms of the surface displacement, urrounding displacement and stress to the existing tunnel and the surrounding rock. Different excavation of footage influents displacement and stress of existing tunnel differently.Having analyzed the features and shortcomings of traditional yield approach index, a new definition of YAI(yield approach index) which focus on the shortest stress path has been presented basing on a studing about the absolute length of rock stress path under the Mohr-coulomb yield criterion, while yield approach functions for several yield criterions have been built up under at the same time. Compared with traditional definition, this definition conveyed the influence of ball stress tensor to the YAI. To make a comparative analysis on excavation models using this two different definitions,the effect of approaching excavation can be studied from the point of risk changes of each stress point. Different excavation of footage influents the yield approach index as well as the stress. It comes to the conclusion after analysis that this method is theoretically feasible,which to analyse the effect of approaching excavation by the YAI.