Structural analysis for shallow tunnels in soft soils

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Generally, studies on structural design for bored tunnels focus on moderate to deep tunnels (cover-to-diameter ratio C/D ≥ 2). Such tunnel design methods cannot be used for shallow-situated bored tunnels because the influence of buoyancy is discounted, and actual loads on the tunnel lining are not taken into account properly. This paper proposes a new model that has more accurate loads on the tunnel lining combined with finite-element analysis for shallow tunnels. Internal forces and deformations of various shallow bored tunnels are investigated. The relationship between the optimal thickness-to-diameter ratio d/D of the tunnel cross section and the cover-to-diameter ratio C/D is also studied.