Failure of rigid support and yielding support solution in large deformation tunnels: A case study

Large deformation often damages the rigid support in a squeezing tunnel. Radial yielding sup-port with a compressible layer is suggested as a solution for large deformation. A compressible layer was constructed between the primary support and secondary lining to absorb time -dependent tunnel deformation. Based on the proposed design method of the yielding support, PE-foam with a density of 90 kg/m(3)-100 kg/m3 was used as the fill material in the compressible layer. The thickness of the PE-foam layer was designed to be 50 mm-100 mm in squeezing mudstone interbedded glutenite. Field application and numerical results demonstrated that although the stress of the primary support may be increased by the high compression of the PE-foam layer, the maximum compression and tension stresses of the secondary lining were only 12.3 MPa and 0.82 MPa, respectively. These were considerably lower than its yield strength, indicating that damage of the secondary lining in the squeezing tunnel was prevented by the PE-foam compressible layer.