Performance of a Zoned Excavation by Bottom-Up Technique in Shanghai Soft Soils

Abstract

This paper investigates a basement excavation adjacent to running metro tunnels and underground pipelines in Shanghai soft soil. The zoned excavation technique was adopted to control the deformations caused by excavation. The excavation site was divided into three parts and successively constructed in the order of Zones A, B, and C with the bottom-up method. The field data of retaining walls, struts, columns, surrounding ground, pipelines, and metro tunnels were monitored and analyzed in terms of lateral and vertical deformations throughout the whole construction process. The data indicates that the wall deflection and column heave in Zones B and C were smaller than those in Zone A. The ground surface settlements near the metro lines were effectively reduced by the zoned excavation technique. The deformations of the metro tunnels and pipelines were well controlled within the acceptable limits. A general relation between wall deflection and the excavation area was also proposed based on this and 15 similar cases.