Study On The Whole Process Of Tunnel Collapse Induced By Large Deformation And Its Prevention And Control Technology

Large deformation is one of the common disasters in tunnel construction in jointed rock mass.If it is not treated timely and effectively,it may lead to major engineering accidents.On April 29,2015,a tunnel of Jinhong Expressway in Yunnan Province was damaged due to improper treatment of large deformation,resulting in a major accident in which the tunnel collapsed and personnel were trapped.Based on this background,this thesis deeply studies the collapse caused by large deformation in tunnel excavation,and has achieved the following innovative results:(1)Based on the evaluation parameters of rock mass in the generalized Hoek-Brown criterion,the fast prediction of tunnel collapse contour was realized by transforming the parameters GSI、mi、D、σci、p in the generalized Hoek-Brown criterion to the parameters A and B in the equivalent tangent equation(σn-τn)form of Hoek-Brown criterion.The effects of different parameters on predicting the collapse contour were also studied.On this basis,the predictive expression of the collapsed contour under complex conditions is further derived.It can be seen from the calculation and analysis of the surrounding rock evaluation parameters that the tunnel has a large risk of collapse.(2)The spatial distribution parameters and mechanical parameters of joints were obtained by field investigation and joint direct shear test.Then the elastoplastic mechanical parameters of rock mass were obtained based on equivalent rock mass technique and displacement back analysis method.These provided a basis for subsequent research.(3)A set of physical model tests was designed,and the device for tunnel model excavation and the displacement monitoring device for surrounding rock were made by ourselves.Combined with theoretical derivation and numerical simulation,the occurrence and development of large deformation,first lining demolition and collapse of tunnel were simulated to the greatest extent.According to the test results,the tunnel vault position was prone to collapse disaster.When the large deformation first support was removed,the positions of the vault and arch foot of the first lining on both sides were prone to tension and shear failure respectively.Therefore,these locations needed to be reinforced in the process of treatment.(4)The finite difference method and discrete element method were mixed used to simulate the deformation and failure characteristics of the surrounding rock of the tunnel after large deformation.It revealed the phenomenon that the stress increases with the increase of displacement in the later stage of large deformation.Then the failure of the surrounding rock blocks and joints during the large deformation process is analyzed,and it was found that the failure range of the joint was much larger than the failure range of the rock blocks.It is more safety if the large deformation treatment time was advanced from 100%to 90%of final deformation.The treatment work needs to be completed within a certain period of time.The distance of each treatment cycle should be the distance between the two steel frames.The research results of this paper have been successfully applied in the construction of Jinhong Expressway tunnel and achieved good engineering results.