Optimization of water-urban-agricultural-ecological land use pattern:A case study of Guanzhong Basin in the southern Loess Plateau of Shaanxi Province,China

Extensive land use will cause many environmental problems.It is an urgent task to improve land use efficiency and optimize land use patterns.In recent years,due to the flow decrease,the Guanzhong Basin in Shaanxi Province is confronted with the problem of insufficient water resources reserve.Based on the Coupled Ground-Water and Surface-Water Flow Model(GSFLOW),this paper evaluates the response of water resources in the basin to changes in land use patterns,optimizes the land use pattern,improves the ecological and economic benefits,and the efficiency of various spatial development,providing a reference for ecological protection and high-quality development of the Yellow River Basin.The research shows that the land use pattern in the Guanzhong Basin should be further optimized.Under the condition of considering ecological and economic development,the percentage change of the optimum area of farmland,forest,grassland,water area,and urban area compared with the current land use area ratio is+2.3,+2.4,-6.1,+0.2,and+1.6,respectively.The economic and ecological value of land increases by14.1%and 3.1%,respectively,and the number of water resources can increase by 2.5%.

Finite-difference model of land subsidence caused by cluster loads in Zhengzhou,China

Groundwater exploitation has been regarded as the main reason for land subsidence in China and thus receives considerable attention from the government and the academic community.Recently,building loads have been identified as another important factor of land subsidence,but researches in this sector have lagged.The effect of a single building load on land subsidence was neglected in many cases owing to the narrow scope and the limited depth of the additional stress in stratum.However,due to the superposition of stresses between buildings,the additional stress of cluster loads is greater than that of a single building load under the same condition,so that the land subsidence caused by cluster loads cannot be neglected.Taking Shamen village in the north of Zhengzhou,China,as an example,a finite-difference model based on the Biot consolidation theory to calculate the land subsidence caused by cluster loads was established in this paper.Cluster loads present the characteristics of large-area loads,and the land subsidence caused by cluster loads can have multiple primary consolidation processes due to the stress superposition of different buildings was shown by the simulation results.Pore water migration distances are longer when the cluster loads with high plot ratio are imposed,so that consolidation takes longer time.The higher the plot ratio is,the deeper the effective deformation is,and thus the greater the land subsidence is.A higher plot ratio also increases the contribution that the deeper stratigraphic layers make to land subsidence.Contrary to the calculated results of land subsidence caused by cluster loads and groundwater recession,the percentage of settlement caused by cluster loads in the total settlement was 49.43%and 55.06%at two simulated monitoring points,respectively.These data suggest that the cluster loads can be one of the main causes of land subsidence.

Groundwater flow through fractured rocks and seepage control in geotechnical engineering: Theories and practices

Groundwater flow through fractured rocks has been recognized as an important issue in many geotechnical engineering practices.Several key aspects of fundamental mechanisms,numerical modeling and engineering applications of flow in fractured rocks are discussed.First,the microscopic mechanisms of fluid flow in fractured rocks,especially under the complex conditions of non-Darcian flow,multiphase flow,rock dissolution,and particle transport,have been revealed through a com-bined effort of visualized experiments and theoretical analysis.Then,laboratory and field methods of characterizing hydraulic properties(e.g.intrinsic permeability,inertial permeability,and unsaturated flow parameters)of fractured rocks in different flow regimes have been proposed.Subsequently,high-performance numerical simulation approaches for large-scale modeling of groundwater flow in frac-tured rocks and aquifers have been developed.Numerical procedures for optimization design of seepage control systems in various settings have also been proposed.Mechanisms of coupled hydro-mechanical processes and control of flow-induced deformation have been discussed.Finally,three case studies are presented to illustrate the applications of the improved theoretical understanding,characterization methods,modeling approaches,and seepage and deformation control strategies to geotechnical engi-neering projects.

Comprehensive Analysis and Artificial Intelligent Simulation of Land Subsidence of Beijing, China

Mechanism and modeling of the land subsidence are complex because of the complicate geological background in Beijing, China. This paper analyzed the spatial relationship between land subsidence and three factors, including the change of groundwater level, the thickness of compressible sediments and the building area by using remote sensing and GIS tools in the upper-middle part of alluvial-proluvial plain fan of the Chaobai River in Beijing. Based on the spatial analysis of the land subsidence and three factors, there exist significant non-linear relationship between the vertical displacement and three factors. The Back Propagation Neural Network (BPN) model combined with Genetic Algorithm (GA) was used to simulate regional distribution of the land subsidence. Results showed that at field scale, the groundwater level and land subsidence showed a significant linear relationship. However, at regional scale, the spatial distribution of groundwater depletion funnel did not overlap with the land subsidence funnel. As to the factor of compressible strata, the places with the biggest compressible strata thickness did not have the largest vertical displacement. The distributions of building area and land subsidence have no obvious spatial relationships. The BPN-GA model simulation results illustrated that the accuracy of the trained model during fifty years is acceptable with an error of 51% of verification data less than 20 mm and the average of the absolute error about 32 mm. The BPN model could be utilized to simulate the general distribution of land subsidence in the study area. Overall, this work contributes to better understand the complex relationship between the land subsidence and three influencing factors. And the distribution of the land subsidence can be simulated by the trained BPN-GA model with the limited available dada and acceptable accuracy.

Changes of groundwater flow field of Luanhe River Delta under the human activities and its impact on the ecological environment in the past 30 years

The Luanhe River Delta is located in the center of the Circum-Bohai Sea Economic Zone.It enjoys rapid economic and social development while suffering relatively water scarcity.The overexploitation of groundwater in the Luanhe River Delta in recent years has caused the continuous drop of groundwater level and serious environmental and geological problems.This study systematically analyzes the evolution characteristics of the population,economy,and groundwater exploitation in the Luanhe River Delta and summarizes the change patterns of the groundwater flow regime in different aquifers in the Luanhe River Delta according to previous water resource assessment data as well as the latest groundwater survey results.Through comparison of major source/sink terms and groundwater resources,the study reveals the impacts of human activities on the groundwater resources and ecological environment in the study area over the past 30 years from 1990 to 2020.The results are as follows.The average annual drop rate of shallow groundwater and the deep groundwater in the centers of depression cones is 0.4 m and 1.64 m,respectively in the Luanhe River Delta in the past 30 years.The depression cones of shallow and deep groundwater in the study area cover an area of 545.32 km^(2)and 548.79 km^(2),respectively,accounting for more than 10%of the total area of the Luanhe River Delta.Overexploitation of groundwater has further aggravated land subsidence.As a result,two large-scale subsidence centers have formed,with a maximum subsidence rate of up to 120 mm/a.The drop of groundwater level has induced some ecological problems in the Luanhe River Delta area,such as the zero flow and water quality deterioration of rivers and continuous shrinkage of natural wetlands and water.Meanwhile,the proportion of natural wetland area to the total wetland area has been decreased from 99%to 8%and the water area from 1776 km^(2)to 263 km^(2).These results will provide data for groundwater overexploitation control,land subsidence prevention,and ecological restoration in plains and provide services for water resources management and national land space planning.

区域地面沉降研究进展与展望

地面沉降是全球性重大地质环境问题,区域差异性地面沉降已经对城市基础设施、线性轨道交通和地下空间开发利用形成重大威胁,制约着经济和社会的可持续发展。围绕区域地表形变信息获取、地面沉降演变机制和模拟方面的研究进展进行系统阐述,重点分析了InSAR形变监测和多源形变数据融合的区域地表形变信息获取技术,基于室内土工试验数据和长时序观测数据,利用相关分析、统计分析和机器学习等方法分析地面沉降演变与各影响因素的关系。在此基础上,探讨了地下水流场—土体变形模型、数理统计模型和机器学习模型等地面沉降过程模拟模型的优缺点。发现多源形变数据融合能够提高区域地表形变信息的时空分辨率,地质构造、地层岩性、地下水开采和动静载荷等影响因素的差异性是造成地面沉降差异性演化的机制,地面沉降数学模型的计算效率与可解释性难以兼顾是当前沉降模拟存在的主要问题。据文献检索,当前研究主要关注地下水超量开采引发的地面沉降。进而提出未来区域地面沉降研究方向:在气候变化叠加新水情、新数据背景下,充分融合遥感大数据与野外观测站实测小数据集,耦合基于物理机制的模型和机器学习模型,优化集成InSAR、GeoAI、云平台等技术的最新进展,揭示全球气候变化和人类活动综合作用下的区域地面沉降演变机制,为区域地面沉降防控和城市安全提供技术支撑。

基于MODFLOW的BP神经网络模型对地面沉降的模拟研究

针对区域性地面沉降问题,文章运用MODFLOW软件中的水井子程序包,在地面沉降监测点处设置了虚拟水位观测井,以虚拟水井模拟的年均水位和统计的年开采量作为输入,各监测点的年沉降量作为输出,引入并构建了BP神经网络模型。对区内6个控沉点的沉降量预测结果表明,随着开采量的减少和水位的回升,地面沉降趋于缓和。同时,作者对BP神经网络模型的物理意义进行了有益的探索性研究。

Simulation of regional land subsidence in the southern Yangtze Delta

Investigation of the deformation characteristics of individual hydrostratigraphic units is the key to construct a regional land subsidence model. All of 12 hydrostratigraphic units in the study area were discussed throughout. On the basis of the measured data of groundwater level, five kinds of changing patterns of groundwater level were deduced and the relationship between the deformation characteris-tics of aquifer units and the corresponding changing patterns of groundwater level was discussed. The study area is 1.7×104 km2, where the geological condition is complex. The changing patterns of groundwater level the hydrostratigraphic units have experienced vary from site to site and from time to time. Consequently, the deformation characteristics of units are sophisticated. An identical hydros-tratigraphic unit may exhibit different deformation characteristics, such as elasticity, elasto-plasticity, visco-elasticity, and visco-elasto-plasticity, at different sites or during different periods, not to mention the different units. The existing models are difficult to describe the complex visco-elasto-plastic con-stitutive law under the condition of land subsidence. So the Merchant’s model was modified to depict the visco-elasto-plastic behavior of units. Then a three-dimensional flow model with variable parame-ters and a vertical one-dimensional subsidence model were constructed and coupled. The coupled model was applied in simulating land subsidence in the southern Yangtze Delta and a satisfactory re-sult was obtained. The simulation results show that the new coupled model can depict the complex geological conditions and describe the developing process of land subsidence very well in the south-ern Yangtze Delta. The new model can surely be used to predict land subsidence in the future, which is very helpful to taking measurements to control land subsidence.

基于MODFLOW地下水数值模拟对济南北部地区地面沉降的预测

为查明济南北部地区深层地下水开采影响地面沉降的成因机理,在综合分析区内水文地质、工程地质、地下水开采等资料的基础上,基于Visual MODFLOW三维有限差分地下水流动模型,对深层地下水降落漏斗发育情况进行了数值模拟,得出地下水流场时空动态分布规律,建立了流-固耦合模型,并对区内地面沉降发展趋势进行了预测。经验证,预测沉降速率与InSAR监测地面沉降速率基本吻合,预测结果基本可靠,具有较高的研究意义和应用前景。

裂隙地下水渗流及溶质迁移数学模型研究进展

针对裂隙地下水渗流及溶质迁移多场耦合数学模型,综述模型研究的发展历程与阶段性成果,将现有模型划分为基于不同介质概化的等效孔隙介质模型、多重介质模型、离散裂隙模型,基于不同耦合方法的非全耦合模型与全耦合模型,以及基于不同模型推导途径的力学途径模型与混合耦合理论模型。针对该领域研究的关键科学问题总结其发展趋势,探讨裂隙地下水渗流及溶质迁移多场耦合数学模型研究的难点及潜在发展方向,为裂隙地下水流及溶质迁移研究提供理论参考。

分布式地表水-地下水耦合数值模型研究进展

系统梳理地表、地下各水文过程中常见的控制方程以及数值求解方法,指出单一地下水模型和单一地表水模型在解决耦合问题中的短板。回顾近年来的相关研究,归纳出11种常见的耦合模型。从模型原理和适用方向2个方面对已有研究概括总结,将耦合方法划分为松散耦合型、半松散耦合型和紧密耦合型,分析耦合模型在变化环境下的地下水-地表水转化关系、河道生态流量以及地表水-地下水联合调度方面的应用。未来可以重点关注耦合模型在复杂地貌、多样化参数、模型识别验证方法、运算效率以及多学科交叉等方面的研究。

苏锡常地区非线性地面沉降耦合模型研究

长期过量开采地下水所引发的地面沉降是一个复杂的非线性变化过程,对其进行数值模拟时,如不考虑沉降发展过程中模型参数的非线性变化,会给预测带来很大误差。本文依据苏锡常地区实际资料,通过典型钻孔土力学试验,确定出土体在不同荷载条件下的弹塑性和蠕变特征方程以及土体渗透系数随孔隙度变化的关系式。在此基础上建立了研究区三维变系数地下水流模型及考虑土体垂向不同变化特征(弹塑变或蠕变)的一维区域沉降模型,并采用多尺度有限单元法对模型进行了真正意义上的耦合求解。

第四纪松散沉积层地下水疏降与地面沉降三维全耦合数值模拟

针对第四纪松散沉积层地下水疏降引起的地面沉降问题,以比奥固结理论为基础,考虑土体的非线性特征及土的渗透性随应力状态的动态变化,将地下水渗流场和土体应力场耦合起来,建立了地下水疏降与地面沉降变形的水土全耦合三维数学模型,并采用三维有限元数值分析方法,以上海市地铁四号线董家渡段隧道修复深基坑降水为例,模拟预测了基坑中心水位降至标高-23.4 m时基坑周围地下水渗流场与地面沉降变形场的分布特征。该模型稳定性好,收敛速度快,能模拟复杂三维地质体和整个基坑降水工程的结构,具有重要的工程实用价值。

天津市地下水流-地面沉降耦合模型

天津市平原区地面沉降主要由地下水大量开采引起,影响范围广、危害大,已成为天津市主要的环境地质问题。分析了研究区的水文地质条件,结合地下水开发利用状况,将研究区概化为6个含水层组,地下水流考虑三维非稳定流,地面沉降选用一维固结压缩模型,运用地下水流模型Modflow 2005和地面沉降模拟模块Sub,建立了天津市平原区地下水流-地面沉降数值耦合模型,模型面积为1.1×104 km2,利用1998—2008年地下水位等值线、过程线、地面沉降过程线等资料对模型进行了识别。模拟期的地下水均衡分析表明,在多年开采条件下,越流补给、压缩释水、侧向边界流入分别占深层含水层补给量的41.84%、32.15%和24.17%。将调试后的模型应用于南水北调实施后地下水控采条件下的地面沉降趋势预测,显示出停采或减少地下水的开采,有利于减缓地面沉降下降速度,且表现出开采层位越往下,地面沉降恢复难度越大的变化趋势。

基于地下水渗流方程的三维地面沉降模型

针对地下水抽取引起的大面积地面沉降的问题,提出了一种计算方法。该方法基于饱和与不饱和岩土介质中地下水渗流理论,计算出三维状态下的大面积地面沉降。提出的方法被结合到地下水渗流的三维有限元法分析中,计算时考虑了地层的可压缩性,并被用来分析软土的固结,将该法与太沙基理论及固结试验的结果进行比较,结果表明其误差小于2%。该法还被用来分析单井抽取承压地下水引起的周围地基的沉降及承压水层由于挡水板的阻断作用而引起的下游侧的地基的沉降。

Biot固结理论在地面沉降计算中的应用

在回顾地面沉降研究现状的基础上,提出采用Biot固结理论进行由降水形成的渗流场与应力场的耦合分析,并运用二维Biot固结平面有限元程序计算因开采地下水而引起的地面沉降问题,最后通过工程实例验证了该方法的可行性。

基于EVS Pro的3D地质建模

为了了解污染物在地层中的分布情况以及地下水开采后产生的结果,在环渤海地区地质构造研究的基础上,利用EVS Pro3维地质建模软件,以天津市(含环渤海地区)74个实测钻孔数据、38个化学污染物的实测钻孔数据为依据,实现了对该地区含水层及地下水漏斗的3维模拟,为解决环渤海地区污染物的控制以及合理有效开采地下水提供了模型支持。

松散承压含水层地区深基坑降水三维渗流与地面沉降耦合模型

以上海环球金融中心基坑降水为例,根据基坑降水过程中有效应力和孔隙水压力的转化关系,建立了基坑降水与地面沉降的耦合模型,并采用有限差分数值模拟方法,模拟了在多层含水层复合存在、含水层最深底板埋深达145 m、基坑周围挡水连续墙埋深达34 m、抽水井埋深达55 m、抽水井过滤器埋深为34～55 m,单井抽水量为1420 m3/d的8口抽水井联合降水情况下,基坑中心下伏第Ⅰ承压含水层上部降压段水位降至埋深26 m时的地下水复杂流动状态及其地面沉降特征。经后续工程验证,该结果正确、可靠,该理论用于模拟预测此类地区深基坑降水引起的地下水流场变化及其地面沉降具有较高的可信度。

地下水开采与地面沉降控制三维全耦合模型研究

针对第四纪松散沉积层中地下水开采所引起的地面沉降问题,以比奥固结理论为基础,考虑到土体的非线性特征及土体的渗透性随应力状态的动态变化,引入邓肯-张非线性模型和渗透率动态模型,将地下水渗流场和土体应力场耦合起来,并以吴江市浅层地下水开采为例,建立了浅层地下水开采与地面沉降三维全耦合数值模型。在对模型进行校正、识别的基础上,以微承压含水层未来10 a内地下水位埋深不低于含水层顶板、地面沉降量不超过50 mm为约束条件,预测了吴江市各镇的地下水可采资源量合计为1203.59×104m3/a。

高层建筑物荷载与地下水开采叠加作用下的地面沉降特征

在地下水开采和高层建筑荷载叠加作用下,城市地面沉降分布愈加复杂。以天津塘沽地区为例,考虑到土体在固结沉降中的平衡条件、弹性本构条件、变形协调条件和水流连续条件,以比奥固结理论为基础,建立了高层建筑荷载和地下水开采叠加作用下三维地面沉降模型,采用有限元方法进行了数值计算。结果表明,高层建筑物的附加荷载作用在其建成后的3~4 a内将产生可观的地面沉降量;抽水和高层建筑荷载叠加作用下的地面沉降存在耦合效应,叠加作用下的地面沉降值小于可比条件下单独抽水和单独荷载作用下地面沉降值之和。