Loose Quaternary deposits are widely distributed in Suzhou,where extracting groundwater has caused a large-scale land subsidence.The land subsidence influences the development of economy.Optical fibers are laid in a 200m borehole drilled in Shengze,Suzhou.Based on the BOTDR and FBG technologies,the Quaternary sediments deformation and land subsidence are long-term monitored.It is showed that Quaternary sediments can be divided into different aquifers(Af)and aquitards(Ad).The main compaction occurs at two thick aquitards which adjacent to the second confined aquifer.In addition,the shorter the distance between the aquitard and the pumping aquifer is,the greater the degree of compression of the aquitard is .The soil layer reaches the maximum compression in summer while a small rebound occurs in winter,showing the conformance with the pore water pressure of the pumping aquifer.We define the compression degree as the ratio of the accumulative compression and the thickness of this layer(i.e.,the unit compression).At this stage the subsidence trend can be judged by compression degree. For the aquitards,there is a tendency shows that Ad2 >Ad3 >Ad4 >Ad1.For the aquifers,the Af2 is the main compaction layer while Af1 and Af3 remain almost constant.DFOS technique provides a very advanced monitoring method for the study of land subsidence mechanism and the evaluation of soil compression deformation potential.%苏州地区广泛分布松散第四纪沉积物,大量抽取地下水导致了苏州大范围的地面沉降,严重影响了该区经济发展.本文在苏州盛泽 200m 钻孔内安装了分布式感测光纤,采用 BOTDR 及 FBG 等分布式光纤感测技术(DFOS),对第四纪沉积层压缩及地面沉降进行了长期的监测分析.分析结果表明:苏州盛泽地区第四纪土层可分为 3 个含水层(Af)及 4 个弱透水层(Ad),现阶段含水层压缩已不明显,主要压缩层为与抽水含水层相邻的两个隔水层,且与抽水含水层距离越近的部位压缩越明显;第四纪沉积层的变形与抽水含水层孔隙水压变化基本一致,呈现出夏季压缩,冬季略回弹的趋势,并且存在滞后现象;定义压缩度为各层累计压缩量与其自身厚度的比值,即每米压缩量.各土层沉降趋势可用压缩度判断,对于黏土隔水层沉降程度 Ad2>Ad3>Ad4>Ad1,对于含水砂层,Af2 为主要变形层,Af1 及 Af3 变形基本稳定.DFOS 技术为研究地面沉降机理,评价土层压缩变形潜力提供了十分先进的监测手段.
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