The performance of geotechnical structures in unsaturated soils is affected significantly by the hydraulic conditions. In the present paper, a unified computational upper bound limit analysis method is applied to study the stability of dual circular tunnels located in unsaturated soils. The linings are substituted by an equivalent uniform pressure exerted on the periphery of the tunnel. The main focus is put on the effect of ground water table and surface water infiltration on the required supporting pressure and collapse mechanisms of dual tunnels. The critical center-to-center spacing above which the interaction of the tunnels disappears is also discussed.
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