Dynamic stress concentration and damping mechanism of twin cylindrical composite-lined tunnels subjected to vertical incident plane SV waves

A series of solutions are presented for the dynamic stress concentration factor of the underground twin cylindrical tunnels with composite liners and buffer layers in a half elastic space subjected to vertically incident plane SV waves based on the Fourier-Bessel expansion method, and the mechanical model for the tunnels with small clear distance with soft layer is established. The influences of the factors such as the distance between the tunnels and the damping layer are investigated. It is shown that the distance between the tunnels plays an important role in the dynamic stress concentration factor of the composite-linned tunnels, and the dynamic stress of the liners decreases when the distance of the tunnels increases. The interaction of the two tunnels must be considered when the distance between the centers of the cavities is less than 4 times the diameter of the chamber. The dynamic stress concentration factor of the surrounding rock in the middle part between the tunnels is larger than that at the other parts. With the low shear modulus of the damping layer, the normal force between the wall rock and the liner is weakened, then the dynamic stress of the liners decreases by 20% with the buffer layers set between the surrounding rock and the liner, while the tangential dynamic stress of the surrounding rock increases.