苏锡常地区深层地下水禁采后土层变形特征分析

STUDY ON THE DEFORMATION CHARACTERISTICS OF SOIL LAYERS AFTER BANNING GROUNDWATER PUMPING IN SU-XI-CHANG AREA

为了控制苏锡常地区的地面沉降,2000年开始该区实行了深层地下水的禁采。基于近10年来监测数据,对比分析了禁采前后地质环境要素的变化规律,重点剖析禁采后地下水回升条件下的土层变形特征。数据分析结果显示,禁采以来,以主采层第Ⅱ承压含水层为代表的地下水位逐步回升,自2000年至2009年,40m埋深水位降落漏斗面积由近4000km^2缩小至1200km^2。地面沉降的发展速率也出现不同程度的减缓,至2008年,大于5mm/a的沉降区面积已缩减到1200km^2。研究区土层的变形特征表现出明显的差异性。苏州北部沿江地区和中部地区地面沉降出现了明显回弹,土层表现为弹性变形特征。而位于地下水位漏斗和沉降漏斗中心附近的土层表现出沉降的迟滞性,即使在禁采后水位回升的情况下土层仍表现为持续沉降或微沉。研究结果为后续区域地面沉降模型中土层沉降模型的合理选择提供依据。

The strict ban of the deep groundwater pumping has been undertaken within a given period since 2000 in order to control the land subsidence in Suzhou-Wuxi-Changzhou area.According to the long-term monitoring data of land subsidence and groundwater level in the recent ten years,the characteristics of land subsidence and groundwater level was analyzed before and after the ban of groundwater withdrawal,with focus on the deformation features after the period of groundwater exploitation ban.Taking the 2nd confined aquifer for example,it was found that the groundwater level was recovered gradually and the area of depression cone of buried depth of groundwater level of 40m was reduced from 4000km2 in 2000 to 1200km2 in 2009.Correspondingly,the rate of land subsidence was slow down and the area of the subsidence rate greater than 5mm/a was reduced to 1200km2 in 2008.More importantly,the deformation characteristics of soil layers are different depending on the location of the depression cone.The ground rebound occurred in the area in north and middle of Suzhou along Yangtze River,which means the deformation in this subarea is basically elastic.However,the land kept subsiding in the area located in the depression cones of groundwater water and land subsidence although the groundwater level rises rapidly over the last years,which indicates a delayed deformation feature.It is important to develop different subsidence models for soil layers according to these results in the further step to build the regional land subsidence model.