Laboratory Test and Numerical Simulation for Geotextile Bag with Sand Cofferdam of Immersed Tunnel

The mechanical indexes of the geotextile and filling sand were obtained by laboratory test based on geotextile bag with sand cofferdam of Zhoutouzui immersed tunnel in Guangzhou, and a fine calculation model was established. The deformation development law of geotextile bag with sand cofferdam was explored by refined numerical calculation. Combining with the existing research results, the deformation mechanism was determined. Numerical results were verified by theoretical analysis and the control index of design and construction was proposed. The results show that cofferdam moves to the side of dry dock under the action of unbalanced pressure, and the displacement decreases from the top to the bottom. Cofferdam appears settlement under gravity and pumping action as well as the displacement increases with the pumping water level decline. The main reason of cofferdam's large deformation is density increase caused by dewatering, which increases overlying pressure from upper geotextile bag to lower one and makes geotextile flattening deformation. Foundation soil experiences vertical pressure consolidation, lateral extrusion and local sliding, which causes the maximum and minimum deformation present to the top and toe of geotextile bag. The cofferdam has no sliding failure and is in overall stability as well as the numerical results are consistent with results deduced by theoretical analysis, so the cofferdam should take the height as the control index.