Stability Analysis Of Shield Tunneling Face Considering Soil Arching Effect

In the process of large number of shield tunnel construction,it is a very important problem to control the land subsidence in the permitted scope.The key to control the ground subsidence is to control the size of the support force of the shield,which is the main control condition for maintaining the stability of the excavation surface and limiting the deformation of the soil above the tunnel.The failure mode of tunnel excavation surface based on the limit analysis method has obtained a lot of research results,and the calculation expressions of limit support force tend to be diversified,but scholars seldom study the effect of soil arch effect on the size of ultimate support.Based on the limit analysis upper limit method,the stability of the excavation face is analyzed under the condition of considering the soil arch effect,and the numerical simulation is used,and the above theory is verified by the engineering example.The main work is summarized as follows:1.Based on the single block failure mode of Leca,the expression of the ultimate support force of the shield tunnel surface is obtained by considering the lateral soil pressure of the surrounding soil and the limit analysis upper limit method.The lateral soil pressure of the surrounding soil is equivalent to "partial cohesive force" because of the rigid body hypothesis of the block and surrounding soil in the failure mode of the Leca single block.2.FLAC3 D software is used to simulate the deformation and failure of the soil in front of the shield tunnel,and the size of the ultimate support force is obtained.Compared with the theoretical results of Leca single block and the soil arch effect,the results of numerical simulation are more close to the ultimate support force obtained in this paper.3.A case study of Beijing metro line eight Tianqiao station to the entrance of Yongding gate is analyzed,and the ultimate support force of the excavation face is obtained,which is closer to the ultimate supporting force calculated in this paper,and the scientific nature of the shield excavation face theory considering the soil arch effect is verified again.4.Finally,the influence of tunnel burying depth,shield diameter,cohesive force of soil and internal friction angle on the ultimate supporting force of excavation face is explored.With the increase of tunnel diameter,the ultimate support stress ratio increases gradually,and the limit support increases gradually.With the increase of tunnel cohesion and internal friction angle,the limit support stress ratio decreases gradually and the limit support decreases gradually.With the increase of the shield depth,the limit support stress ratio and the limit support of the open excavation face are increased.The force increases slightly,and the amplitude is small...