Characteristics and parameters of sand strata deformation due to groundwater pumping in Shanghai

Severe land subsidence took place in Shanghai due to long-term pumping of groundwater.Based on the observation data of soil strata deformation and groundwater table the relationship between the deformation characteristics of sand strata and the variation of groundwater tables is studied.It is found that in the periods of groundwater table ascending or keeping steady the sand strata exhibit elastic behavior.Whereas,in the period of descending the sand strata exhibits elasto-plastic behavior when the groundwater table is higher than the lowest in the history.A bilinear elasto-plastic model can be used to describe this behavior.The sand strata exhibit visco-elasto-plastic behavior when the groundwater table is lower than the lowest.A model in which a spring arranged in parallel with the Bingham body and serially connected with another spring can be used to depict the visco-elasto-plastic behaviors of sands.The deformation parameters of sand strata are determined according to the obtained data and provide the basis for the calculation of land subsidence.