Abstract
In this paper, the hydrogeological features of Quaternary deposits in Shanghai as well as the characteristics of groundwater withdrawal and recharge in urban areas are investigated. One phreatic aquifer and five confined aquifers (AqI to AqV) are present in Shanghai, and these aquifers are separated by five aquitards. Groundwater withdrawal from confined aquifers has resulted in land subsidence in Shanghai. To control land subsidence, the groundwater withdrawal volume has been decreased, and the groundwater recharge volume has been increased since 1965. Correspondingly, the pressure head in confined aquifers has risen. The groundwater head increases in shallow aquifers may impact underground structures and lead to the following issues: i) an increased risk of water in-rushing hazards caused by confined water pressure during structural excavations and ii) an increased instability risk caused by groundwater buoyancy. Both excavation anti-uprush and underground structure anti-floating are discussed in this paper. Based on the risk possibilities, the anti-uprush of the excavation is divided into six regions, and the structural anti-floating is divided into five regions in urban areas. To avoid geohazards caused by the rise in groundwater head, real-time monitoring of the pressure head in AqII is recommended.
Highlights
Land subsidence is a geological phenomenon closely related with human beings
The unit weight of soil is taken as 18.5 kN/m3, the unit weight of water is taken as 10 kN/m3, and the pressure head is the highest water head during the 2012 to 2015 period in each region
When the groundwater head a confined aquifer rises, Thisinto study the amount of groundwater withdrawal andingroundwater recharge in the water head in theeffects adjacent aquifers willofincrease to the leakage effectBased between
Summary
Land subsidence is a geological phenomenon closely related with human beings. It causes many geologic hazards, e.g., destruction of urban infrastructures, tilting of buildings, variation of groundwater environment, and ground fissures. Human activities are an important factor for land subsidence, including engineering construction and groundwater withdrawal. In China, land subsidence was first discovered in the 1920s in Shanghai and Tianjin, and it had become very serious in the 1960s in these two cities. There are nearly 100 cities in China whose ground subsidence is mainly the result of groundwater withdrawal, and 80% of these cities are distributed in eastern China. The Yangtze River Delta Plain is the most typical area of land subsidence in China, including Shanghai, Su-Xi-Chang area, and Hang-Jia-Hu plain.
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