The effect of sloping grounds on the seismic response of tunnels

In this paper the seismic response of tunnels in the sloping grounds is analyzed by means of elasto-plastic finite element method and using quasi-static analysis. The circular tunnels are modeled in the sloping ground and at depths of ۵, ۱۰, ۲۵ and ۳۵ meters in the shale rocks. The tunnels are supported by end anchored rock bolts with length of ۳ meters and spacing of ۲ meters. The seismic loading is done for different earthquakes and horizontal and vertical acceleration coefficients are calculated for different depths. The axial force of rock bolts are measured for each of the acceleration coefficients of earthquakes. The results of the evaluations show that the most changes of rock bolts axial force is related to case that the horizontal seismic coefficient (Kh) apply in the same direction as dip of ground surface. Moreover, the strength factor of rock masses around the tunnels has reduced with increasing the dip of ground surface and as a result the changes of rock bolt axial force have increased for all earthquakes. The most impact of earthquake on the rock bolt axial force in slopes is related to shallow tunnels and this effect decreases with increasing depth tunnels.

Keywords:

Seismic response , Circular tunnels , Sloping ground