Study On Stability Analysis And Safety Control Technology Of Deep Buried Tunnel Based On Strain Softening Model

The YanChong Expressway is the main transportation supporting project for the 2022 Olympic Winter Games in Beijing.The Yudushan Tunnel,as an important part of the YanChong Expressway,is characterized by long line,deep burial depth and unfavourable geological conditions.The Yudushan Tunnel is the key to whether the YanChong Expressway can be completed on schedule.Shortly after the start of the Yudushan Tunnel project,collapse accidents of various sizes occurred,causing serious construction delays and economic losses.The occurrence of these accidents aroused the great attention of the engineering construction units,and then the scientific research aimed at the safe construction of the Yudushan Tunnel was launched.The author participated in the three-year research work of the project as one of the main members.Based on this project,the thesis takes the instability mechanism of deep buried tunnel strain softening surrounding rock as the research object,and aims to formulate safety control measures for the deep buried tunnels.The following innovative results have been achieved:(1)A method for solving the engineering response of the deep buried tunnel surrounding rock suitable for different strength criteria is established.The correlation mechanism between the elasto-plastic solution of the strain softening surrounding rock of the deep buried tunnel and the variation of strength criterion is revealed systematically.And on this basis,the dynamic prediction of the extent of the broken rock zone of the deep buried tunnel surrounding rock is preliminarily realized.Considering the strain softening characteristics of rock and non-associated flow rule comprehensively,a new strain component characterization function of the potential plastic zone of the deep buried circular tunnel is derived.A method for solving the nonlinear mechanical response mechanism of the surrounding rock of the tunnel excavation is established.This method not only has the characteristics of the traditional method,but also covers the elasto-plastic solution of the elastic-perfectly plastic and the plastic-brittle-plastic rock tunnel.The elasto-plastic unified solution equation for the deep buried tunnel is derived,which can reflect the strength criterion effect.Suggestions for selecting suitable strength criteria in the process of the tunnel engineering stability evaluation and the support design are given.It lays a foundation for the study and engineering application of the stability control of the deep buried tunnel surrounding rock.(2)The characterization method for the support characteristic curve of tunnel surrounding rock is optimized and improved.The bearing mechanism of the primary support structure of the tunnel and its relationship with the strain softening surrounding rock are well revealed.The whole process of the dynamic interaction between the strain softening surrounding rock and the primary support of the deep buried tunnel is analyzed.The mechanical analysis model of the surface primary support is established considering the steel arch,steel fabric and sprayed concrete.The analytical formula which can fully reflect the mechanical bearing nature of the surface primary support is derived.The mechanical bearing effects of the different component combinations in the primary support system are revealed.A new solution of the support characteristic curve of the tunnel surrounding rock considering the steel arch,steel fabric,sprayed concrete and anchor support is established.The determination method of the maximum support force and the support stiffness of the primary support system is clarified.The quantitative influencing factors of the support characteristic curve of the tunnel surrounding rock are revealed.It provides useful references for the safety evaluation and construction design of the deep buried tunnel.(3)The optimization of the supporting time of the primary support is realized by adopting the failure approach index.A new primary support design method suitable for the strain softening surrounding rock is established based on determining the optimal supporting time.A technical plan for the safety control of the surrounding rock of the deep buried tunnel is proposed,which achieves ideal engineering results.For the first time,the failure approach index is adopted to optimize the supporting time.On the basis of proposing the concepts of critical stress release rate and the critical displacement release coefficient,the optimal supporting time design method of the primary support system for the strain softening surrounding rock of the deep buried tunnel is established.The scientific and dynamic adjustment of the primary support system is realized.Combined with the physical model test,the necessity of the double-layer primary support in the safety control of the surrounding rock of the deep buried tunnel is clarified.The surrounding rock safety control plan of "enhanced reservation+double-row small pipe and pre-grouting support+three-benching seven-steps excavation+double-layer primary support+non-uniform anchoring and grouting reinforcement" is designed,and the ideal engineering results is achieved.