An innovative earth retaining supported system for deep excavation

The U-shape wall is an innovative application of a composite buttress-cross wall to reduce excessive movements induced by excavation. The performance and mechanism of the U-shape wall in controlling the deformations were examined by three-dimension finite element analysis. The examination includes the buttress part treatment of the U-shape wall (i.e., demolished or maintained), the length of the buttress part, the depth of the cross part, and the deformation control mechanism of the U-shape wall. Results revealed that the buttress part treatment of the U-shape wall was insignificant. Moreover, the normalized depth of the cross part to final excavation depth ratio was 0.15-0.2 that can yield optimum performance. Also, the design of the length of the buttress part relies on the target value of the reduction. For example, with a 5 m length of the buttress part, the deformations could be reduced by 60-80% from the case of without U-shape wall. The deformation control mechanism of the U-shape wall was notably contributed to the combined stiffness between the U-shape wall and the diaphragm wall.