上海市城市化进程引起的地面沉降因素分析

20世纪90年代上海中心城区的地面沉降在地下水开采量没有增加的情况下出现了新一轮的增长。与此同时,上海进行了大规模的城市化建设。通过对中心城区地面沉降量与工程建设进行相关性分析发现,近年来中心城区的地面沉降量与工程建设具有相关性。目前城市化建设引起地面沉降的现象已受到关注,但尚缺乏对城市化进程引起地面沉降机制的系统研究。针对上海市城市化进程引起地面沉降的因素进行分析探讨,城市化进程引起的沉降包括建筑物荷载及交通荷载等外荷载引起的沉降,基坑开挖、降水及隧道施工等工程施工引起的土体压缩,以及隧道渗漏,周边地区对地下水补给量的减小,地下构筑物挡水效应等引起的地下水位持续下降而诱发的沉降     

Evaluation of allowable withdrawn volume of groundwater based on observed data

To control land subsidence due to groundwater withdrawal, it is important to estimate allowable withdrawn volume of groundwater in a soft deposit. This technical note presents a simple approach for estimating the allowable withdrawn volume of a deposit. A regression analysis method was used based on measured land subsidence and recorded net withdrawn volume. This approach was proposed based on the principle of soil compression at different effective stresses, i.e. the soil compression is small when the consolidation stress is lower than the yield stress of the deposit, but large when the consolidation stress is higher than the yield stress. Two case studies are presented in this technical paper to demonstrate how to use the simple approach to estimate the allowable withdrawn volume.     

The development and control of the land subsidence in the Yangtze Delta,China

Land subsidence in China occurs predominantly in 17 provinces (cities) situated in the eastern and middle regions of the country, including Shanghai, Tianjin and Jiangsu, and Hebei provinces. It is primarily caused by groundwater overpumping. One of the areas most severely affected by land subsidence is the Yangtze Delta, most of which consists of Shanghai City, the Su-Xi-Chang area (Suzhou, Wuxi and Changzhou cities) of Jiangsu Province, and the Hang-Jia-Hu area (Hangzhou, Jiaxing and Huzhou cities) of Zhejiang Province. The excessive exploitation of groundwater forms in a large regional cone of depression and, consequently, land subsidence is also regional, currently centered in the Shanghai and Su-Xi-Chang areas. In 2002, the maximum cumulative subsidence of Shanghai, Su-Xi-Chang and Hang-Jia-Hu were 2.63 m, 2.00 and 1.06 m, respectively. The land subsidence area is continuing to expand throughout the Yangtze Delta. To study the characteristics and the pattern of this land subsidence, the government has implemented a monitoring system involving the placement of 37 groups of extensometers (layers marks) and drilling of more than 1000 observation wells. These provide an invaluable historical record of deformation and pore water pressure and facilitate studies on the special features of soil deformation when the groundwater level changes due to pumping. Several measures have been taken in recent years to control the development of the land subsidence in the different areas; these include groundwater injection, prohibition of pumping deep confined groundwater, and an adjustment of the pumping depth and magnitude of the groundwater withdrawn. At present, although the subsidence area is still increasing slowly, the subsidence rate is controlled.     

Evaluation of land subsidence by considering underground structures that penetrate the aquifers of Shanghai, China

Underground structures that penetrate into aquifers can cause groundwater-level drawdown and land subsidence. Numerical analyses, based on a three-dimensional (3-D) groundwater flow model incorporated with a 1-D consolidation model, have been conducted to assess the behaviour of seepage and effect on subsidence by considering underground structures in the multi-aquifer?Caquitard system of Shanghai, China. Two extreme scenarios were examined: (1) distributed underground structures, and (2) concentrated underground structures around the heavily urbanized area. In the first scenario, the aquifer with underground structures was substituted with another material that possessed a lower hydraulic conductivity, established using the effective-medium theory; when the ratio of the volume of the underground structures to that of selected aquifer layers??(1) low-pressure partially-confined aquifer (Aq02), (2) the first confined aquifer (AqI), and (3) the second confined aquifer (AqII)??increases by 10?%, subsidence increases by about 3, 3 and 32?%, respectively. In the second scenario, part of the aquifer material was directly replaced by the structure material (very low hydraulic conductivity). In this situation, when the ratio of the volume of the underground structure to the volume of aquifers Aq02, AqI or AqII increases by 10?%, subsidence increases by about 5, 8 or 20?%, respectively.     

地下水位变化模式下含水砂层变形特征及上海地面沉降特征分析

土体变形特征与其经历的应力状态有关。由于抽灌水位置和水量的变化,同一土层中不同时期的地下水位可以呈现不同的变化模式,土层表现出不同的变形特征。论文根据上海1400多个水位孔近40a的水位观测资料和各土层的变形资料,从土层变形角度将地下水位的变化方式划分为5种模式。分析了每种地下水位变化模式下土层的变形特征,并进一步分析了上海地面沉降在时间和空间上的特征。分析结果表明:地下水位的变化模式对上海土层的变形有显著影响。同一土层在不同的水位变化模式下可表现为弹性、弹塑性或粘弹塑性的变形特征;地面沉降与地下水开采量、地下水开采层次与主要沉降层具有密切的关系,开采地下水是上海地面沉降的主要原因;与现阶段含水层的水位变化模式相联系,第四承压含水层是上海最近几年来地面沉降的主要沉降层。     

水位与沉降双控模式下浅层地下水压力回灌试验研究

通过浅层地下水压力回灌对比试验研究,掌握上海地区特殊地质条件下浅层地下水回灌技术工艺,并对浅层地下水压力回灌技术控制地面沉降的效果进行了分析。研究表明,采用变压力、变流量地下水人工回灌可有效实现地下水位和地面沉降的双重控制,效果显著,可有效应用于上海地区地下空间开发引发的工程性地面沉降防治实践。     

滨海地区深基坑减压降水地面沉降研究成果及应用——以上海市为例

针对地下空间开发中深基坑减压降水地面沉降发育特征、沉降机制及防治对策等研究进展,以上海市为例,总结了近年来滨海地区深基坑减压降水地面沉降研究取得的主要成果。建立了深基坑减压降水地面沉降防治综合分区方法,探索了深基坑减压降水地面沉降防治原型试验设计方法,掌握了上海市浅部承压含水层深基坑减压降水地面沉降规律,提出了深基坑减压降水地面沉降-地下水位双控模式及控制指标,提出了深基坑减压降水地面沉降防治措施,构建了深基坑减压降水地面沉降管控体系。这些研究成果在特大型城市安全管理、重大市政工程建设及运营服务中得到应用,对同类地区地面沉降研究和防治工作具有借鉴意义。     

Modelling the cutoff behavior of underground structure in multi-aquifer-aquitard groundwater system

The quaternary deposit of Shanghai is composed of an alternated multi-aquifer-aquitard system (MAAS) consisting of a sequence of aquitards laid over aquifers one by one. In the MAAS, any drawdown of groundwater head in an aquifer may cause consolidation of the overburden aquitard. When underground structures penetrate those aquifers, groundwater seepage path changes and drawdown occurs at the side characterized by the lower hydraulic potential along the flow direction (hereafter refers as to the lower side). This drawdown may cause additional subsidence at the lower side and unbalanced load between the two sides of the underground structure. In order to evaluate the cutoff effect of an underground structure on groundwater seepage in a MAAS representative of the underground of the city of Shanghai, a numerical analysis based on a groundwater flow model has been carried out. The simulated results have shown that underground structures which cut off groundwater flow locally change both magnitude and direction of the flow velocity field. The induced changes in the groundwater field are highly sensitive to the penetration depth and width of the underground structure. Design recommendations for underground structures in aquifers belonging to a MAAS are also presented, which has not yet been considered in the engineering practice of Shanghai.     

Regional land subsidence simulation in Su-Xi-Chang area and Shanghai City, China

Su-Xi-Chang area and Shanghai City, located in the south of Yangtze Delta, China, has subsided due to groundwater overpumping. Because of the regional scale of the groundwater exploitation, cone of depression and land subsidence at present, Su-Xi-Chang area and Shanghai City are treated as a single area for land subsidence study to avoid the uncertainty of boundary condition due to the regionalism. The characteristics of aquifer system compaction are complex because of the difference in the types, compositions and structures of the soils that the hydrostratigraphic units are composed of, and in the histories of groundwater level change the hydrostratigraphic units have experienced. Considering the fact that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics, such as elasticity, elasto-plasticity, and visco-elasto-plasticity, at different sites of the cone of depression or in different periods, corresponding constitutive laws have been adopted. This avoids the shortcomings of the previous research that the same constitutive law was adopted in all the hydrostratigraphic units during the entire time period. A coupled flow and subsidence model, which includes a three-dimensional flow model with variable coefficients and a one-dimensional (vertical) subsidence model, is built according to the complicated hydrological condition in the region. The simulation model is calibrated using observed data, which include compression of individual strata from groups of extensometers and groundwater levels from observation wells from 1995 to 2002. The model reproduced that the primary subsidence layer in Shanghai shifts from the shallow aquitard to the fourth confined aquifer because of the groundwater yield variations and the change of exploitation aquifers. However the third aquitard was the primary subsidence layer in Su-Xi-Chang area and the compaction deformation of the sandy aquifers was remarkable. The simulation results could provide some reasonable advice about groundwater exploitation in the future.     

黄河三角洲典型地段地面沉降机理研究及预测预警

随着社会经济的快速发展,黄河三角洲地区普遍发生了地面沉降,已经成为了影响区域社会经济可持续发展的重要因素之一。本文以黄河三角洲地面沉降典型地段—滨州地区为研究对象,以该区2005~2019年年间共计6期地面沉降监测数据为基础,对区内多年来地面沉降发展演变规律进行分析,对地面沉降成因机理进行研究,并根据滨州地下水系统的水文地质条件以及地面沉降机理,概化出滨州地下水系统水位地质概念模型及地面沉降模型。在此模型基础上推演建立滨州地下水开采与地面沉降三维数值模型。利用该模型对地面沉降与地下水位监测数据进行内插外推计算,综合计算结果分析和研究,对地面沉降和地下水动态进行预测预警,从而为黄河三角洲地区地面沉降防治提供依据。     

Three-dimensional numerical modeling of land subsidence in Shanghai,China

Shanghai, in China, has experienced two periods of rapid land subsidence mainly caused by groundwater exploitation related to economic and population growth. The first period occurred during 1956–1965 and was characterized by an average land subsidence rate of 83 mm/yr, and the second period occurred during 1990–1998 with an average subsidence rate of 16 mm/yr. Owing to the establishment of monitoring networks for groundwater levels and land subsidence, a valuable dataset has been collected since the 1960s and used to develop regional land subsidence models applied to manage groundwater resources and mitigate land subsidence. The previous geomechanical modeling approaches to simulate land subsidence were based on one-dimensional (1D) vertical stress and deformation. In this study, a numerical model of land subsidence is developed to simulate explicitly coupled three-dimensional (3D) groundwater flow and 3D aquifer-system displacements in downtown Shanghai from 30 December 1979 to 30 December 1995. The model is calibrated using piezometric, geodetic-leveling, and borehole extensometer measurements made during the 16-year simulation period. The 3D model satisfactorily reproduces the measured piezometric and deformation observations. For the first time, the capability exists to provide some preliminary estimations on the horizontal displacement field associated with the well-known land subsidence in Shanghai and for which no measurements are available. The simulated horizontal displacements peak at 11 mm, i.e. less than 10 % of the simulated maximum land subsidence, and seems too small to seriously damage infrastructure such as the subways (metro lines) in the center area of Shanghai.     

2001-2020年上海市地面沉降灾害经济损失评估

地面沉降是加速潮灾、涝灾等自然灾害的风险源.由于上海市市政建设和高层建筑的建设以及周边地区继续抽取地下水的影响,地面沉降趋势仍在继续.这使上海市在未来必将遭受地面沉降灾害所产生的巨大经济损失.分析了上海市未来地面沉降灾害产生经济损失的可能性、损失程度等.通过对影响未来地面沉降灾害经济损失不确定因素的分析,运用统计方法评估了2001-2020年间上海市地面沉降灾害风险的经济损失.经评估,2001-2020年上海区地面沉降灾害风险经济损失总额为245.7亿元.     

开采浅层地下水对地面沉降影响的探讨

苏锡常地区由于长期过量开采深层地下水，已诱发了严重的地面沉降灾害。为此，江苏省政府下达了在2005年全面禁采深层地下水的文件。为解决用水问题，许多专家、学者建议开采利用浅层地下水。在苏锡常地区开采浅层地下水是否会同样诱发严重的地面沉降问题，是目前争议的焦点。文章详述了苏锡常地区水文地质条件及地面沉降现状，确定了地面沉降的各种影响因素，分析对比了浅层地下水与深层地下水在开采条件下所能引起的地面沉降量，说明采用合理的开采工艺开发利用浅层地下水不会诱发严重的地面沉降。     

广州金沙洲岩溶区地下水位变化与地面塌陷及地面沉降关系探讨

金沙洲可溶性灰岩分布面积广,岩溶洞隙发育,洞隙及地下水的连通性强,上覆第四系松散土体中软土广泛分布,客观存在岩溶地面塌陷及地面沉降的地质环境条件。2007年4月起,受某高铁隧道施工抽排地下水的影响,金沙洲地下水出现异常波动,引发了地面塌陷及地面沉降。文章根据监测数据,经对比分析结果表明,区内岩溶地面塌陷及地面沉降受控于地下水位的变化,地下水位波动至基岩面附近时,是地面塌陷较活跃的时期,地面沉降与地下水位变化呈正向相关。文章进一步对地面沉降与地下水位变化关系的机理进行了探讨,认为目前地下水位尚未恢复正常的区域仍存在地面塌陷及地面沉降的隐患。     

Long-term groundwater storage changes and land subsidence development in the North China Plain (1971–2015)

The North China Plain (NCP) has been suffering from groundwater storage (GWS) depletion and land subsidence for a long period. This paper collects data on GWS changes and land subsidence from in situ groundwater-level measurements, literature, and satellite observations to provide an overview of the evolution of the aquifer system during 1971–2015 with a focus on the sub-regional variations. It is found that the GWS showed a prolonged declining rate of ?17.8?±?0.1 mm/yr during 1971–2015, with a negative correlation to groundwater abstraction before year ~2000 and a positive correlation after ~2000. Statistical correlations between subsidence rate and the GWS anomaly (GWSA), groundwater abstraction, and annual precipitation show that the land subsidence in three sub-regions (Beijing, Tianjin, and Hebei) represents different temporal variations due to varying driver factors. Continuous drought caused intensive GWS depletion (?76.1?±?6.5 mm/yr) and land subsidence in Beijing during 1999–2012. Negative correlations between total groundwater abstraction and land subsidence exhibited after the 1980s indicate that it may be questionable to infer subsidence from regional abstraction data. Instead, the GWSA generally provides a reliable correlation with subsidence. This study highlights the spatio-temporal variabilities of GWS depletion and land subsidence in the NCP under natural and anthropogenic impacts, and the importance of GWS changes for understanding land subsidence development.     

苏州城市规划区Ⅱ承压水开采与地面沉降预防控制研究

在孔隙承压水开采与地面沉降的关系上存在2种观点。水、土应力平衡理论认为：只要开采承压水，就会引发应力失衡并导致地面沉降；而水、土动态平衡理论则认为：除非开采水压力至水、土应力平衡面以下，否则不会引发地面沉降。苏州城市规划区第Ⅱ承压水开采水位与地面沉降动态观测表明，在-33m处存在一个天然动态水、土应力平衡面。第Ⅱ承压含水层形成后，经上覆堆积物自重压力长期压缩作用，其水压力具较高的压强．这种天然状态下产生的弹性释放储存量可开采利用多少，取决于开采状态下水、土应力平衡时可消耗压力水柱高度中的水头值。因而地面沉降的根本原因是开采水位超过了-33m，突破了天然状态水、土应力平衡面水位。Ⅱ承压含水层在天然状态受上覆堆积物重力产生的高压强弹性释放储存量现象，可以帮助我们确立该地区孔隙Ⅱ承压水开采不产生地面沉降的临界水位(水、土应力平衡面)。这一点对承压水开采条件、可开采资源性质具有重大实际意义。同样可以应用于饱受地面沉降困扰的无锡、常州及周边地区，为地下水开发利用政策由单一的封井停采转为目标水位控制开采提供了科学依据。同时也为此政策在承压水动力学机制上找到了内在原因。     

天津滨海新区地面沉降层位的精准识别与沉降过程重建

塘沽地区地面沉降是新生代松散沉积物多层位沉降叠加的结果,精准识别各层位的沉降贡献是该区地面沉降防控的关键。利用塘沽G2地面沉降分层标组2011—2014年观测数据,对新生代沉积物不同层位的地面沉降进行了精准识别;结合以前的分层标观测资料,重建了1960年以来不同层位的地面沉降过程。结果显示,在1960—1970年地下水开发初期,地面沉降主要层位是浅部粘性土自然固结和第二含水组地下水开采;1970—1980年深层地下水开采高峰期,主沉降层位由二组逐渐加深到三、四组;1985年以后实施了地面沉降控制措施后,第四系地下水开采引起的地面沉降逐渐减小;2000年之后,随着滨海新区的成立和大规模的城市建设,城市建设引起的建筑基础沉降逐渐成为主要的沉降层。通过对不同时期主要地面沉降层位的转换过程分析,提出地面沉降精准防治新思路。     

基于ANN的苏锡常地裂缝预测研究

伴随着地面沉降灾害的发生,地裂缝作为一种新的地质灾害出现在苏锡常平原上,已有十多年历史,给地区发展造成严重危害。作者在较详细地阐述区域地质背景基础上,着重分析了地下水位和地面沉降在地裂缝形成中的作用。确定了“起伏的基底外加地下水位和地面沉降作用”这一地裂缝成灾模式。研究认为地裂缝的发生与地下水及地面沉降之间不存在简单的线性关系。而是二者共同作用的结果,同时需要有量的配合。初步确定了水位埋深50m,地面沉降量达500mm这样一个苏锡常地区地裂缝的易发环境。通过文章的研究,使得苏锡常地区地裂缝的产生机制更加清晰。文中一些定性和半定量的分析结论将对该地区地裂缝防治区划产生指导作用。     

天津市汉沽区深层地下水演变研究

根据天津市汉沽区地下水历史资料,分析区域地下水开采量、水位埋深、地面沉降变化及它们之间的联系等。发现汉沽区地下水处于长期超采状态,地下水位也呈逐年下降趋势,地面不断下沉,地下水的过量开采是引起地面沉降和水位持续下降的主要原因。通过建立汉沽区地下水流-地面沉降模型,设定三个水平年地下水开采方案,预测未来地下水位埋深及地面沉降变化。预测表明,随着地下水开采量的消减,地下水位逐步上升,地面下沉趋势可得到遏制。     

上海市地下水位大幅抬升条件下土层变形特征分析

过去对地下水位持续下降条件的地面沉降研究较多,但对水位大幅持续抬升过程中的地面沉降研究较少。本文根据 上海大量地面沉降、水位观测和钻孔资料,系统分析上海市90年代末以来地下水位大幅抬升条件下各土层的变形特征。自 1998年以来,上海市通过大幅压缩开采量、回灌地下水等措施使第二、三、四和五承压含水层水位分别平均抬升2.1 m, 3.6 m, 12.4 m, 12.7 m。水位的抬升使上海市地面沉降平均速率由1998年的12.2 mm/a减小到2011年的1.83 mm/a,减少85%。 通过对27组分层标数据分析发现：现阶段主要压缩层位在第一、二软土层,年沉降速率为2~4 mm/a;而第二含水层以下土 层已经有少量回弹。在水位持续大幅抬升过程中,本文总结了两种变形特征：1） 变形和水位变化基本同步,残余变形量非 常小,变形可概化为线弹性变形,这种变形主要发生在第一、二、三和五承压含水层、第五和六弱透水层;2） 压缩速率逐 渐减小,无明显持续回弹趋势,有较大残余压缩量且存在变形滞后现象,变形可概化为弹塑性变形,这种变形主要发生在 地第二、三和四弱透水层。第四承压含水层变形较复杂,两种变形特征都有。其中较大残余变形量主要由塑性贮水率比弹 性贮水率大2个数量级引起;变形滞后主要由弱透水层中超孔隙水压力消散较慢引起。本文研究成果对于掌握水位抬升过 程中土层变形方式、发生发展机理、预测未来地面沉降及地下水科学管理和资源评价具有重要意义。