Abstract: Based on an upgrading project of a wastewater treatment plant in Beijing and combined with the need of owner’s operation requirements, this paper presents the design conception and the construction technique of the wastewater treatment plant. The entire upgrading project site has a water depth of 10.5 meters and the staged construction divided the original site into two parts by a sandbag cofferdam with one side maintained the normal operation, and the other side was dewatered and excavated. Combined with the results from the finite element analysis software PLAXIS 2D and the construction monitoring data, it is technically feasible to use the sandbag cofferdam as water retaining structure in the deepwater dewatering requirements. This project can provide some guidance or references for projects with similar background and conditions.

Key words: underwater deep excavation, cofferdam using sandbag, finite element analysis, water retention structure