Monitoring and Analysis of Deep Foundation Pit Construction of Structural Loess in Northwest China

Abstract

To investigate the internal force and deformation characteristics of the supporting structure of structural loess foundation pit, 15 field monitoring data of foundation pits in Shaanxi, Gansu and Ningxia, were collected. The lateral movement of the supporting structure, settlement of soil behind piles and axial force of supporting point were studied on the basis of induction and systemize. The results show that: (1) due to the influence of spatial effect, the pile lateral displacement, surface settlement at the corner of foundation pit were significantly smaller than the middle of foundation pit; (2) the pile maximum lateral displacement at the middle of foundation pit ranges from 0.8 %” ∼ 2.0 %” of excavation depth, the pile top lateral displacement ranges from 0.2 %” ∼ 0.6 %” of excavation depth, the lateral displacement at the corner of foundation pit decreased by 60% ∼ 70%; (3) the maximum surface settlement in the middle of the foundation pit can reach 0.35%<r∼1.2%o of the excavation depth, and the maximum settlement at the corner of foundation pit decreased by 60% ∼ 70%; (4) the position of largest axial force of supporting point occurs near the maximum lateral displacement, between 0.4 ∼ 0.8 of excavation depth, the maximum measured axial force of the supporting point reached 35% ∼ 80% of the designed axial force, indicated that many foundation pits were too conservative in the design process, the structural characteristics of loess in northwest area should be considered, and the design scheme of the foundation pit should be optimized to save the cost of foundation pit engineering to avoid unnecessary waste.