Design and practice of deep foundation pit engineering under sensitive conditions in soft soil area

Based on the successful engineering practice for the underground garage of a hospital in Shanghai, the design and practice for the underground garage under the congested urban housing environment in Shanghai soft soil area are presented. The garage is close to nine existing buildings including two historical buildings whose protection requirements are extremely high. According to the characteristics of the project, the temporary retaining and bracing system combined with the substructure of the underground garage and the top-down construction method are adopted. Precast diaphragm walls first applied in two-storey underground garage in Shanghai soft soil are used as the temporary retaining wall combined with the exterior wall of the garage . In order to reduce the settlement of buildings caused by deep excavation, protective measures including shut-off screens between the retaining wall and the existing buildings and the pile underpinning technique for the foundation of the existing buildings are applied. The practice shows that the settlement of the buildings meets the requirements through adopting the above-mentioned technical measures, and the safety of the surrounding environment is ensured. This project provides a reference for other similar underground space development projects in Shanghai area.