Numerical simulation research on shock absorption of mountain tunnel portal section in highly seismic region

The research about shock absorption of mountainous tunnel portal is fairly hard to see now. The entry portal of NO.2 Huangcaoping Tunnel located on State Highway of NO.318 is selected as the prototype and use the finite difference software FLAC3D 3.0 to study the protected length of tunnel portal for earthquake and the influence of lining stiffness on seismic response, and to analyze the damping effect of setting buffer layer in lateral direction and axial direction and of reinforcing the surrounding rock, and finally summarize the points and the synthetically measures for shock absorption. The results show that after about 25~30m to go deep into tunnel, the amplification effect of seismic wave gets stable and this distance can be used as reference to specify the protected length for earthquake-resistance, that too large stiffness of lining will expand the seismic damage, that setting lateral buffer layer and setting axial buffer layer can both significantly decrease the seismic response and make the stress get even, and what’s more, the effect of the former seems better than the latter, that enforcing wall rock with bolts can effectively reduce the seismic load on lining and this effect seems especially good for weak wall rock. Finally, the suggestion is put forward that synthetically measures for vibration absorption should be adopted and the lining stiffness should be balanced for seismic safety design of mountainous tunnel portal.