Simple approach to assessing excess pore water pressure induced by shield tunneling in saturated-unsaturated clay soil.

Excess pore water pressure (EPWP) induced by shield tunneling has a significant influence on the stability of the tunnel face, post-construction settlement, and the mechanical behavior of the tunnel lining. However, the three-dimensional and unsaturated property of the soil field is seldom considered in current research. Considering the non-uniform radial convergence model, a modified three-dimensional displacement solution induced by shield tunneling was established first. Then based on unsaturated EPWP elastic theory, a reliable and efficient method is developed to expedite the evaluation of EPWP distribution in three-dimensional saturated and unsaturated clay soil. The validity of the method is confirmed through comparison with field test and numerical outcomes. The analysis examples demonstrate that negative and positive EPWP are generated above the tunnel crown and beneath the tunnel invert, respectively. In the vertical direction, the negative EPWP exhibits a decreasing trend ahead of the heading face and an increasing trend behind it. Along the longitudinal direction, the influence zone of EPWP extends to 1D ahead of and 6D behind the heading face. With the decrease of soil saturation, the EPWP values tend to diminish. The maximum EPWP values observed in saturated conditions can be 16.13 times higher than those under unsaturated conditions. [ABSTRACT FROM AUTHOR]