The Geological Characteristics and Design Scheme of the Nariobi-Malaba Railway Through the Great Rift Valley
In order to select appropriate safety measures for the railway tunnel crossing the active fault zone,taking the Ngong tunnel in the eastern wing of the East African Rift Valley as an example,a combination of field geological investigation and theoretical analysis methods were employed to conduct targeted research on the geological structure within the fault zone through which the tunnel passes.The geological characteristics and fault activity were summarized and evaluated,and the impact on the tunnel project was inferred,leading to the formulation of specialized design principles and plans for the tunnel.The study reveals that the active faults in the tunnel project area are distributed in the form of steeply inclined normal faults.When a magnitude 7 earthquake occurs,the fault zone crossed by the tunnel will experience an average vertical displacement of 0.9 meters.In response to these foreseeable geological hazards in the rift valley areas,avoidance or prevention measures should be implemented during the initial design phase.The research results suggest the following:(1)The route should avoid geologically unfavorable strata as much as possible.If avoidance is not feasible,structures such as tunnels and embankments with large angles should be used for easy repair.(2)Considering post-earthquake reparability,sufficient redundancy should be included in the design of longitudinal curve elements to meet the requirements for slope adjustment after an earthquake.(3)In the initial construction phase,the outline of the secondary lining structure of the tunnel should be designed to be inclusive,ensuring that the post-disaster tunnel interior meets the clearance requirements for normal train passage.(4)To meet the post-earthquake repair needs,special designs should be made for the track substructure within the tunnel,the suspension method of the overhead contact system,the form of water drainage cable troughs,and the segmental structure of the tunnel,so that the tunnel has the ability to quickly recover and resume normal use after an earthquake.
Nariobi-Malaba RailwayThe Great Rift Valleyactive fracture zoneNgong tunneldesign schemegeological characteristics
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