| Ever since the birth of shield method, with the advantages of its security and stability, the method has gradually become the main tunnel construction method. Especially in recent years, the construction of the subways and river tunnels in our major cities has promoted the development of shield construction. During the excavation of the shield tunneling process, it’s inevitable that the principal stress axes of the soil will rotate due to soil stress release, and the problem was encountered frequently and overlooked. So it’s necessary to consider the impact of the principal stress axis rotation of the soil during tunnel excavation.The thesis takes the north line of the river tunnel of Weisan Road in Nanjing as the background, and uses the three-dimensional finite difference software-Flac3D to simulate a section of the tunnel construction process. The principal stress axes rotation of the soil will have an impact on soil internal friction angle, so during the numerical calculation, it’s necessary to change the soil internal friction angle as the excavation to study the impact of the principal axes rotation.According to the calculation results, it’s found that before the tunnel face reached the soil’s rotation of principal stress which is in a distance of2m ahead of tunnel face is completed. Before the excavation, the maximum principal stress direction of the soil around the tunnel is vertical, with the excavation, the direction is parallel with the tunnel contour.Make the contrast with the calculation results of considering the rotation of principal stress or not, the maximum ground subsidence is greater when considering the rotation and the development of the scope of the plastic zone is essentially the same. The scope of the plastic zone of the tunnel is gradually increasing with the excavation and then steady when the excavation passes the study face. The influence scope of the plastic zone enlarges one time when considering the rotation. |
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