An analytical model of loosening earth pressure in front of tunnel face for deep-buried shield tunnels in sand

Abstract

For deep-buried shield tunnels in sand, it is difficult to determine the loosening earth pressure in front of tunnel face due to the significant soil arching effect during excavation. Considering the soil arching effect and the correlation between the relative displacement of soil and the arching deformation patterns, this paper proposed a new analytical model of loosening earth pressure in front of tunnel face. This soil arching effect refers to the load transfer of parabolic soil arch, the height of shear bands and the lateral stress ratio on both sides of rectangular arch. Formulas for calculating the three-dimensional loosening earth pressure were deduced. Then the reliability of this model was verified through comparing the results from the proposed model and the three-dimensional trapdoor experiments. Subsequently, this model of loosening earth pressure was introduced into a five-truncated cones model to compute the limit support pressure on tunnel face. Finally, comparisons of the proposed model and classical models as well as typical centrifuge model tests were conducted. Comparative analysis shows the proposed model of loosening earth pressure excels the classical models, and the failure zone predicted by the proposed model is in good agreement with that obtained from centrifuge model test.