Abstract:

The elastic modulus of the materials filled in the karst caves under the tunnel floor is smaller than that of the surrounding rock, which affects the stress of the lining and, in the end, causes lining cracks. In the paper, the stress and displacement of the lining of a tunnel with filled karst caves under its floor are calculated on basis of Winkle elastic foundation beam theory and the calculation results are compared and analyzed on basis of numerical simulation results. Conclusions drawn are as follows: 1) The materials filled in the karst caves play a supporting role for the tunnel lining and causes large shear force and bending moment at the boundary between the karst caves and the surrounding rocks; 2) The tensile stress of the lining at the karst cave positions increases rapidly, therefore, the structural reinforcement of the lining at these positions should be strengthened, i.e., antibending steel bars and antishear steel bars should be added to improve the tensile and shear capacity of the structure so as to avoid cracks; 3) Efforts should be made to ensure that the elastic modulus of the materials filled in the karst caves is close to that of the surrounding rock as much as possible to improve the stress state of the lining at the karst cave positions.

Key words: Baishan tunnel, karst cave, crack, elastic foundation beam, filling material, elastic modulus