An Innovative Technology to Control Groundwater during Excavation over Confined Aquifer

When excavation is conducted near confined aquifers of the soft deposit of Shanghai, quicksand and piping failure may occur. To prevent the possible Geo-hazards, dewatering in aquifers is generally conducted with arrays of deep wells. If groundwater is pumped out from both phreatic aquifer and confined aquifer, two sets of wells are installed; the first set of wells pumps groundwater from the phreatic aquifer; and the other one pumps groundwater from the confined aquifer. Dewatering system with two sets of wells is widely employed in field works, but it is not economic. To minimize construction costs, an innovative technology called two functions of one well (TFOW) is developed. In TFOW, one set of wells penetrates into the confined aquifer with a valve box installed at the depth of aquitard inside the well. The valve is shut down to pump groundwater from the phreatic aquifer and is opened to pump groundwater from the confined aquifer. This paper introduces the TFOW technology in the beginning and then presents field tests. Results of the field test show that there is no significant impact on the surrounding environment with TFOW technology.