The effect of face support pressure on tunnel face displacement and surface settlement in EPB tunneling method

Determining an appropriate range of face support pressure is an important parameter in mechanized tunneling in urban areas، to preventing face instability، providing the necessary conditions for advancing through controlling settlements. There are many studies using numerical methods to determine the effects of applying various face pressures on the surface deformation. Most of them are for a specified case and also generally expressing that increasing the pressure causes reduction in the amount of surface settlement. In this article the effect of applying various face pressures on the tunnel face displacement and surface settlement has been studied. three-dimensional numerical models using finite difference method and Sensitivity analysis on excavation depth and environment parameters were performed. It was observed that in all cases، increasing pressure causes a significant reduction in the amount of surface settlement at the beginning of the session، Then the amount of the impact is low and finally، by using higher pressures، in addition to creating a heave in the front، the amount of settlement will increase. In larger depths and smaller angles of internal friction، the settlement increasing sensitivity to increasing face support pressure in a specific amount، is higher. Also it can be said that face displacement sensitivity to face support pressure in the environments with different angles of internal friction، different cohesions or in different excavation depths are relatively identical. It means that by increasing the face pressure in a specified value، the amount of movements in two conditions will be close. While this is not true in the case of environments with different deformability modules.