Behavior and optimal analysis of double-layered cantilever soldier-pile retaining structure subjected to basement supplement beneath existing building
Tang Deqi1,2 Yu Feng1,2 Huang Xiangguo3 Liu Nianwu1,2 Xie Zhengbing3
1. Institute of Foundation and Structure Technologies, Zhejiang Sci-Tech University, Hangzhou 310018, China；
2. Zhejiang Provincial Engineering and Technology Research Center of Assembly-Concrete Industrialized Buildings, Hangzhou 310018, China；
3. Wuhan Municipal Construction Group Co., Ltd., Wuhan 430023, China
Abstract：Underground space supplement by excavation beneath constructed basement usually encounters the situation that existing and newly-created retaining piles form a double-layered retaining structure. This is a new issue that traditional excavation design methods have not involved. On the basis of model-test results, a finite element analysis is carried out to investigate the bearing mechanism and the failure mode of such special retaining structure. The parametric studies involve the influence of the length ratio of the two-layer piles and the row spacing on the safety factor of excavation and the force sharing of the two retaining rows. The research shows that the safety factor increases with decreasing the pile-row spacing, leading the supplementary retaining piles transferred from replacement elements in the active soil to be the principal bearing elements and the overall overturning failure of the retaining structure. When the row spacing is relatively large, the overturning failure is caused by the existing piles alone, and soil slip surface is limited to the soil between the pile rows, while the newly-added support piles and the soil behind these piles have been little affected. Within a certain length range, increase of the length of the new support piles will effectively increase the safety factor of excavation and the force sharing effect. Such effect is more obvious for smaller spacing of the pile rows. The optimal solution for the arrangement of new support piles is obtained by comprehensively evaluating the maximum value of the bending moments of the new-existing two-stage support piles, the sum and the safety factor of the support.
