Visco-elasto-plastic compaction of aquitards due to groundwater withdrawal in Shanghai, China

Abstract

Long-term excessive groundwater withdrawal can cause aquifer systems to compact, and land subsidence ensues. The compaction of aquitards lags behind the change of groundwater level in adjacent aquifers, which is attributed to low hydraulic conductivity and great creep deformation of aquitards. Under the condition of groundwater withdrawal, aquitard clays may compact visco-elastically, elasto-plastically or visco-elasto-plastically, depending on the effective stress history they have experienced. Laboratory data manifest that aquitard clays have a similar constitutive relationship to aquifer sands, therefore the double-yielding visco-elasto-plastic mechanical model proposed for aquifer sands is applicable to aquitard clays. A fully coupled one-dimensional visco-elasto-plastic compaction model is constructed for aquitards to predict their compaction by integrating the double-yielding mechanical model with the flow governing equation of groundwater. The comprehensive compaction model not only makes the groundwater flow and soil deformation coupled, but also takes into account the complex deformation characteristics of aquitard units under long-term groundwater withdrawal, such as creep and plastic deformation under reloading.