Model Test Research on the Law of Strata Deformation Induced by Constructing Close-Spaced Tunnel with Subsurface Excavation Method

With the double-hole and single-track tunnel of Dalian Metro Line 1 as example,the optimal ratio of similar materials for soil layers was obtained by similarity principle and uniaxial compression test to construct double-hole and single-track tunnel model in laboratory.The surface displacements at different locations of the model were measured and accordingly the law of strata deformation induced by the successive construction of the left and right tunnels was analyzed.Results show that the ground settlement reaches 70%~80% of the maximum settlement within the first 72h after tunnel construction.The ground settlement is greater in the left-line tunnel which is excavated first.Along with the increase of strata depth,the ground settlement increases gradually and the asymmetricaldouble-peakcharacteristics of ground settlement curve are more obvious.The horizontal ground displacement on the axis of two tunnels approximately decreases linearly with the increase of strata depth.The horizontal ground displacement in the locations of center line and axis of two tunnels is no longer 0.The change of the horizontal ground displacement above both sides of tunnel is the most violent,in which obvious shear layer appears.The original pile and shear wall within this range is liable to crack under additional shear action owing to tunnel excavation.