Effects of groundwater exploitation and recharge on land subsidence and infrastructure settlement patterns in Shanghai

Land subsidence is a severe geo-hazard in coastal regions and represents a great threat to infrastructure. Based on long-term measurement data, including that for deep compaction from vertical multipoint extensometers, land subsidence and infrastructural settlement from leveling surveys, groundwater levels in multiple confined aquifers, and hydrogeological conditions, this study investigates the effects of groundwater exploitation and recharge on land subsidence and the settlement of infrastructure in Shanghai, China. Further, groundwater exploitation and the consequent responses of piezometric heads in the multiple confined aquifers of Shanghai soft deposits are discussed. Subsequently, regional land subsidence, local deep-soil deformation, and infrastructural settlement are analyzed in terms of groundwater exploitation. It is found that the subsidence pattern is related to the trend of groundwater exploitation and the variation of piezometric heads in the aquifers, which can be roughly divided into three phases. Subsidence funnels could occur, and could be interpreted according to the differences in groundwater exploitation intensity and the spatial variability of lithology. Since the towers of Nanpu Bridge are located within the area of the subsidence funnel, this could be the main reason for the differential settlement of the bridge.