Instability Mechanism And Earth Pressure Distribution Model Of Deep Buried Shield Tunnelling Face

With the rapid development of China's social economy and the intensification of urbanization process,the shallow underground space in the core urban area is nearly saturated,and the development of underground space has gradually developed from the normal depth to the deep direction.With the increase of the buried depth of the tunnel,the balance mechanism and stability of the shield excavation face are quite different from that of the conventional buried surface.And because of deep buried tunnel construction design theory shortage,lack of experience,the earth pressure distribution around deep buried tunnel pattern is not very clear,the relevant theoretical research is far behind the engineering practice,the construction the risk and the safety for shield tunneling,excavation face stability control and segment load of deep buried tunnels,has become the deep buried large diameter shield construction in the disaster prevention key environmental problems.Based on the deep buried tunnel project as the research object,a variety of research methods by means of theoretical analysis,physical model test and finite element numerical simulation on excavation face,failure mechanism,mechanical effect,excavation of deep buried tunnel evolution,soil arching effect of excavation,support pressure and failure mode support surface local and global instability limit support pressure and soil pressure around the tunnel to determine the distribution of key scientific problems of deep buried shield,conducted a comprehensive and systematic analysis,the influence of shield tunneling process of earth arch effect on the surrounding environment.The main research work of this paper is as follows:(1)Three-dimensional elastoplastic analysis of mechanical characteristics of shield tunneling in anisotropic soil under undrained conditionsBy using the method of analytic theory,with the help of the cylindrical cavity expansion theory and critical state soil mechanics,combining the modified Cambridge model(K0-MCC Model)constitutive theory,deducing the foundation soil under undrained conditions considering the stress induced anisotropy of the shield excavation mechanics characteristic of 3D elastic-plastic solution.The sensitivity of various factors was discussed.(2)Macro-meso model test for active failure of shield tunneling face in dry sand strataThe model of overall and local active instability failure of shield tunnel face under the conditions of small support under different buried depth conditions was studied by using the method of physical gravity similarity model test.We get the displacement field cloud map of the soil in front of excavation face under different depth to depth ratio by using particle image velocimetry(PIV).And the change of the support pressure and the distribution of soil pressure around the tunnel were monitored and analyzed.(3)Model test of soil pressure distribution around deep buried tunnels considering shield tunnelingA simple device that can simulate the continuous dynamic tunneling process of the shield was developed.Ground settlement and soil pressure distribution of deep and shallow tunnel perturbation difference mechanism of soil were analyzed by using the model test method.And the influence of the soil arch effect on the surrounding soil pressure in the excavation of the deep buried shield tunnel was determined clearly.(4)Active limit support pressure and action load of deep buried shield surface based on soil arch effectThe general solution for the limit pressure of the local shield and the whole instability of the excavation face under any stratum condition was derived considering the rotation of the main stress in the front of the excavation face during the deformation process.And the analytical formula of the action load of the shield tunnel tube was established based on the effect of soil arch effect.Finally,the achievements of this paper were summarized,and the shortcomings and research prospects were discussed separately.It is expected to provide a reference for the stability control of the excavation face and tunnel structure during the construction of deep buried shield tunnel.