北京地面沉降区土体变形特征

因过量开采地下水而引发的地面沉降问题已成为北京平原区最主要的地质灾害。北京地面沉降监测网络从2002年开始建设,到2008年底已经基本覆盖整个平原区。本文基于地面沉降分层标和地下水位监测资料,从土体变形与水位随时间的变化、土体变形和水位的关系出发,分析了不同岩性、不同深度土体在不同的水位变化模式下的压缩变形特征,最终将土体在水位变化下的变形特征概括为5类。结果表明:现阶段北京地面沉降区浅部土体压缩减缓,中深部土体和深部土体多以较快的速度持续压缩。砂层以弹性变形为主;不同埋深的粘性土体存在弹性变形、塑性变形和蠕变变形,具有显著的粘弹塑性。

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

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.