SEISMIC ANALYSIS AND FAULT DISLOCATION DESIGN OF THE TUNNEL THROUGH RIFT VALLEY OF NAIROBI-MALABAR RAILWAY

The Nairobi-Malabar railway runs through the great rift valley, and has tunnels running through many active faults. In the design of tunnel structure, both earthquake and dislocation of fault are considered. In the seismic and seismic design of the tunnel, the tunnel structure is designed as the chain. So the tunnel structure can automatically adjust its deformation with the action of the earthquake and fault dislocation, without causing the overall failure. In order to analyze the seismic response of tunnel structure, a numerical model of dynamic analysis is established. The synthetic time history of acceleration with a probability of over 2%in 100 years is considered as a horizontal seismic action input at the bottom of the numerical model. The response law and chain characteristics of tunnel structure under earthquake are calculated and analyzed. The calculation shows that the chain-like tunnel structure can play a good role in seismic energy dissipation. In addition, due to the dislocation of the fault, the inner limit of the tunnel is reduced, which makes the tunnel loses its normal traffic function. Therefore, in the fault dislocation design, according to the characteristics of the fault and the type of catenary, the tunnel section expansion size is determined comprehensively. When the fault dislocation affects the normal traffic operation, the footwall tunnel can be expanded and backfilled according to the characteristics of the normal fault. Adjusting the slope of the line, the insulation distance of the catenary and the suspension mode can eliminate the dislocation amount of the fault. So the normal passage condition of the line in the tunnel can be achieved, without rebuilding the second lining structure of the tunnel.