Numerical evaluation of segmental tunnel lining with voids in outside backfill

This paper presents a numerical investigation of the mechanical behaviour of segmental linings owing to the existence of voids in the composite lining. The composite lining was formed by mining outside and shield tunnelling inside with backfill in between. Finite element method was conducted to analyse the axial forces and bending moment for voids of different diameters at different positions. The results show that the axial forces in the transverse section increase near the crown and then invert and decrease on the left and right sides with an increase in the void centre angle (beta) measured from the vertical axis. The increase in void diameter (d < 300 mm) induces an increase in the axial force on the left and right sides when beta = 45 degrees and 90 degrees, while it decreases near the crown and invert. The occurrence of voids leads to an increase in the bending moment in the entire segment section with an angle beta.