The deformation behavior of soil mass in the subsidence area of Beijing

Abstract：Land subsidence induced by excessive groundwater withdrawal has constituted a major environmental geological problem in Beijing plain area. The construction of the monitoring network of land subsidence in Beijing began in 2002 and the network had covered the whole plain area by the end of 2008. Based on the data from layered marks and groundwater observation wells, the authors drew curves of variations over time in the aspects of both soil mass deformation and water level and relationship between soil mass deformation and water level, and carried out an analysis of deformation behaviors of soil mass with various lithologic characters at different depths depending on the corresponding water levels. As a result, the deformation behavior of soil mass is generalized into five categories. Some conclusions have been drawn： (i) the deformation rate of the shallow soil mass in the present is slowing down, and most of the mid-deep and deep soil masses are still in continuous compression at a faster speed; (ii) the sand strata are characterized by elastic deformation,and clay soil mass at different depths is usually characterized by elastic-plastic deformation and creep deformation and can be considered to be visco-elastoplastic materials.