Dynamic Stress Concentration and Particle Velocity Response of a Composite Lining Tunnel with Imperfect Interfaces Subjected to Blasting P Waves

The dynamic response of a composite lining tunnel with an isolation layer under blast-induced cylindrical P waves is investigated by using the wavefunction expansion method. The spring model is introduced to simulate the imperfect interfaces between the structural layers of tunnels. Numerical calculations are carried out based on the Xianglu Mountain Tunnel in Southwest China to illustrate the influence of the source-to-tunnel distance, the degree of interface imperfection, and the shear modulus and thickness of the isolation layer on the dynamic stress concentration factor (DSCF), the radial velocity scaling factor (RVSF), and the hoop velocity scaling factor (HVSF) of the final lining. It is concluded that dynamic stress and peak particle velocity in the final lining are strongly affected by the source location, especially under the condition of a small source-to-tunnel distance and a relatively low incident frequency. The DSCF, RVSF, and HVSF for blasting P waves, the frequency of which is below 200 Hz, agree with the corresponding results for far-field plane P waves if the source-to-tunnel distance surpasses 50 times the inner diameter of the tunnel. The interface imperfection tends to weaken the DSCF in the final lining, and its effect on RVSF and HVSF is frequency-dependent. The isolation layer can significantly reduce the dynamic stress and particle velocity response in the final lining.