Dewatering–Induced Building Settlement around a Deep Excavation in Soft Deposit in Tianjin, China

Abstract

This case study presents an investigation on building settlement induced by dewatering for a deep excavation constructed in a deposit in Tianjin, China. The excavation site is located in the Tianjin urban center, around which there are many existing buildings. Geological conditions at the site involve a multiaquifer system with one phreatic aquifer over three confined aquifers. To maintain the stability of the bottom of the excavation, a cutoff wall was used to block groundwater seepage with large diameter wells to lower the groundwater level. Field instrumentation was installed during construction to monitor (1) the quantity of withdrawn groundwater, (2) the groundwater head, and (3) the settlement of surrounding buildings. The field observations yielded the following results and implications: (1) pumping of groundwater could lead to large building settlement and a large area of ground settlement; (2) most of the settlement caused by dewatering did not rebound; (3) the cutoff wall played a significant role in reducing the building settlement during dewatering; and (4) the dewatering-on-demand procedure should be implemented during excavation.