Three-Dimensional Face Stability of Earth Pressure Balance Shield Tunnels Considering Non-Uniform Support and Semi-Open Driving Mode under Seepage Conditions.

This work is motivated to study the face stability of earth pressure balance shield tunnels excavated in the semi-open mode and supported by non-uniform chamber pressure under seepage conditions. Within the kinematic approach of limit analysis, an analytical framework incorporating the seepage effect and linear chamber pressure distribution is developed. The pore pressure distributions are numerically simulated and imported into the three-dimensional (3D) discrete rotational failure mechanism. The work rates caused by the pore pressure and non-uniform support in the semi-open mode are introduced into the work rate balance equation to optimize the critical support pressure. Then, a parametric analysis of three typical soils, including the sand, silt, and clay, is performed to investigate the difference between the semi-open mode and closed mode under seepage conditions. The effects of the muck height and pressure gradient in the chamber, the groundwater levels, and anisotropic permeability are also studied. Finally, several design charts of the normalized critical support are presented. The results show that the difference between considering a linear pressure distribution and a uniform distribution in the semi-open mode is small, with a maximum difference of 3%. Compared to the closed mode, the instability of the tunnel face is significantly higher in the semi-open mode under seepage conditions. [ABSTRACT FROM AUTHOR]