Study On Collapse Mechanism And Treatmentmethod Of Huofengshan Tunnel

Tunnel collapse has been one of the most threatening disasters in tunnel engineering now,it happened with an high frequency and great risk in the process of tunnel construction.While the reasons and mechanisms of tunnel collapse are different in different project for the various geological conditions.So it is imperative to study the collapse mechanisms combining with the geological condition of the project.In the background of Huofengshan tunnel,the tunnel collapse mechanisms and its treatment method were studied by numerical calculation and monitoring measurement.The research conclusions are as follows.1.The collapse mechanism of Huofengshan tunnel is that,the stress of supporting rocky layer is large for the greater thickness of covering soil and the thinner thickness of supporting rocky layer.In addition,the carrying capacity of supporting rocky layer would be reduced by blasting.So the surrounding rock may become unstable.2.The following conclusions about collapse treatment method of Huofengshan tunnel are concluded through the comparison results of various treatment methods.(1)The deeper the grouting depth is,the better the carrying capacity of supporting rocky layer is.While the increase rate of carrying capacity of supporting rocky layer reduces after the grouting depth is more than 4m.(2)The larger the surface grouting area is,the more uniform and symmetrical the stress of surrounding rock.While the range of surface grouting is within 10 m around the collapse area,the stress of upper surrounding rock is exactly symmetrical.(3)The surrounding rock deformation rate of CD method and CRD method are more gentle than step method,it is helpful for stability of surrounding rock.Then the best collapse treatment method of Huofengshan tunnel is that,the grouting depth of surrounding rock is 4.5m,the range of surface grouting is within 10 m around the collapse area,and the construction method is CD method.3.The surrounding rock deformation is normal during construction and finally reach a steady-state by the recommended treatment method,and the collapse control effect is good.