Reverse Calculation and Analysis of Measured Internal Force of Deeply Buried Shield Tunnels with Large Crosssection Under High Water Pressure Conditions

Abstract:

A field monitoring program was performed to measure the steel strain in segments of a shield tunnel deeply buried with high pore water pressure of Nanjing Metro Line 3 project. Concerning the nonlinear properties of concrete and segment joint of tunnel, an improved algorithm was proposed to compute the internal forces of deeply buried shield tunnels under high water pressures based on three existing reverse calculation methods, and the results were compared to the ones computed in structural design. The results show that the improved algorithm can reflect the actual stress state of segments, especially the lining of shield tunnels deeply buried with high pore pressure; the distribution of internal forces calculated in design is almost equal to the one computed by the improved algorithm, but there are some quantitative discrepancies; the axial forces of segments and joints calculated in structural design are approximately half of the backcalculation results; the bending moments of segments calculated by the proposed algorithm are close to the results of the modified routine method at the bottom of the tunnel while approximate the results of the beamspring model at the roof and haunch of the tunnel, and the bending moments of segment joints are greater than the results of the beamspring model. The insights provided from this study can contribute to the improvement of largesection shield lining design.

Key words:shield tunnel; field monitoring; measured steel strain; reverse calculation of internal force in segments