基于马氏链样本模拟的渡槽结构系统可靠度分析

提出了一种适合于渡槽结构系统可靠度计算的重要样本法。该方法根据Metropolis准则构造马尔可夫链模拟样本，通过在失效域中进行预抽样，获得对失效概率的计算贡献较大的重要区域的分布信息，然后利用此信息构造重要样本函数，采用重要样本技术计算结构系统的失效概率。对一典型梁式渡槽进行各种失效模式的分析，建立了相应的功能函数，并就本文算法与已有算法计算得的可靠度进行了比较。结果表明，该方法由于不涉及设计点的概念，解决了应用重要样本法计算系统可靠性时重要样本函数构作的难题，具有较好的效率和精度。     

Optimal Groundwater Remediation Under Uncertainty Using Multi-objective Optimization

A methodology is developed for optimal remediation of groundwater aquifers under hydraulic conductivity uncertainty. A multi-objective management method based on a pump-and-treat remediation technology, is proposed. The pumping rates and well locations are the decision variables and two objectives are chosen: minimization of contaminated groundwater in the aquifer and minimization of remediation cost. A Monte Carlo simulation method is used to cope with hydraulic conductivity uncertainty. A number of equally probable realizations of hydraulic conductivity are created and a Pareto front is obtained using a modified multi-objective Genetic Algorithm. A penalty function is utilized to maintain the algebraic sum of pumping and recharging rates equal to zero. Since Monte Carlo simulations are CPU time consuming, a method is proposed to identify the few significant realizations which have an effect on the optimal solution (critical realizations). A Pareto front with an assigned probability is derived, so that the decision maker can make decisions with specified reliability. In a case study with 100 realizations, only 11 realizations were found critical and need be considered. The remaining 89 realizations consistently obtain low ranks for all designs considered and do not affect decisions at 95% reliability level. Thus these realizations need not be considered which implies a 89% savings in computer time. The designs obtained using the critical realizations, retain a similar reliability for new realizations not considered in the design process.     

三江平原地下水循环演化特征

对三江平原20世纪50—60年代、70—80年代和90年代至今的地下水资源量进行了调查对比,结果表明:低山丘陵区和平原区主要接受大气降水的补给,平原区还接受丘陵区的地下水侧向流补给及河水补给,排泄在早期以蒸发为主,后期以人工开采为主;三江平原地下水循环演化是从20世纪70—80年代开始发生负均衡变化的,而在农业经济发展的90年代负均衡更加显著,形成了一些地下水超采区。     

山西省地下水超采区的复核与评价

利用动态法分析山西省盆地平原区和岩溶山区等重点地区地下水动态变化趋势,结果表明:随着水资源条件、地下水取用水情况等因素的变化,以及地下水超采区治理工作的不断加强,地下水超采状况已发生了较大变化。提出下一步超采区划定中应注意的问题:①基于前期划定成果对重点地区进行补充调查;②盆地平原区仍是复核、评价的重点;③确定峨嵋台地的超采范围;④重点分析洪水泉、郭庄泉对应局部地区,如汾阳杏花村水源地超采情况。     

采用统计矩法计算边坡的破坏概率

本文视影响边坡滑移破坏的因素内摩擦角和凝聚力为随机变量，采用可靠性分析中的统计矩法计算某边坡的破坏概率，并与其它几种方法相比较，结果较吻合，表明该方法用于分析边坡稳定性是可行的，文中同时讨论了内摩擦角和凝聚力的统计分布类型。以及在地下水和地震作用下内摩擦角和凝聚力的变化规律和对边坡破坏概率的影响。     

Groundwater Rise Problem and Risk Evaluation in Major Cities of Arid Lands – Jedddah Case in Kingdom of Saudi Arabia

Arid lands are in the need of additional water supply but water transportation from outside of the natural hydrological cycle causes the groundwater to rise within the urban areas. Additional water supply from surrounding areas or through the desalination plants provides comfort in domestic activities but after the usage, its disposition is necessary in an efficient manner. Unfortunately, arid region cities have neither sufficient nor efficient sewage system. Consequently, the water returned to surface cesspools and leakages from insufficient sewage system makes internal groundwater recharge within the urban area. Additionally, water supply system leakages further raise the groundwater level. Deterioration in water quality becomes a potential danger for the infrastructure and foundations. Surface depressions in the city may be flooded due to groundwater level rise and at times bed smells occur at various parts of the city. In this paper, a quantitative method is followed to assess groundwater level rise risks in addition to the few chemical risks associated with sulfate and chloride solids. It is observed that each one of these variables has different probability distribution function and expose risk maps with different features.     

地下水动态预测模型的回顾与展望

回顾了国内外地下水动态预测研究的各种模型,将这些模型划分为确定性模型和随机模型两大类,指出各种模型的适用条件及存在问题。最后提出了提高地下水动态预测的可靠性与精度的两条途径:(1)建立既能描述地下水系统内部特征也能反映其外部特征的确定性-随机耦合模型;(2)建立地下水系统的随机微分方程模型,并将系统内部参数作为随机变量,将其外部环境因素也作为随机时间序列引入地下水流定解问题,并给出解的概率分布。     

防洪减灾风险管理研究综述

主要对水文风险、水力风险、经济风险、风险决策和洪水保险五个方面的风险管理方法在防洪减灾中的研究现状进行归纳和评述 .其中水文风险的研究重点分为线型选择、参数估计、风险率计算三部分 ;水力风险的研究主要集中在水库泄洪风险及河道或洪泛区的洪水演进研究 ;经济风险分析主要集中在防洪费用效益的风险分析 ;风险决策研究通常表现为防洪问题的可靠性规划和多目标风险分析两种形式 ;洪水保险的研究主要是利用模拟模型来推导一个最优洪水保险策略 .文末阐述了防洪减灾风险管理的发展趋势     

A Framework for Ground Water Management Based on Bayesian Network and MCDM Techniques

Groundwater resources are steadily subjected to increasing water demands. The aquifers are considered as the most accessible source of fresh water. In recent years, they have been faced with severe water withdrawal in arid and semi-arid countries like Iran and thus some aquifers was considered as forbidden aquifers that it means the water withdrawal from these aquifers is unauthorized. Given a critical situation, groundwater resources management in the form of tools such as monitoring the level of the aquifers and developing the restoring scenarios is essential. Therefore, for this purpose, a framework has been developed based on prediction of groundwater level using Bayesian Networks (BNs) model. Furthermore, Multi Criteria Decision Making methods (MCDM) techniques proposed and employed for ranking of proposed groundwater management scenarios. This framework was evaluated for restoring the Birjand aquifer in Iran in different hydrological conditions. A probabilistic Dynamic BN was proposed for groundwater level prediction under uncertainties. After analyzing the obtained results, the applicable short term scenarios for groundwater management as well as appropriate economic, social and technical criteria were defined for decision making procedure. Then, using elicitation of decision makers’ opinions on the relative importance and performance of criteria, SAW, TOPSIS and PROMETHEE-II techniques were applied to rank the scenarios and the obtained results were aggregated by Borda method for final ranking of the scenarios. Lastly, the final results demonstrates the capability of the proposed framework for groundwater resources planning and management which can be employed for reducing the risk of aquifer level declining.     

Interval-parameter Two-stage Stochastic Semi-infinite Programming: Application to Water Resources Management under Uncertainty

In this study, an interval-parameter two-stage stochastic semi-infinite programming (ITSSP) method was developed for water resources management under uncertainty. As a new extension of mathematical programming methods, the developed ITSSP approach has advantages in uncertainty reflection and policy analysis. In order to better account for uncertainties, the ITSSP approach is expressed with discrete intervals, functional intervals and probability density functions. The ITSSP method integrates the two-stage stochastic programming (TSP), interval programming (IP) and semi-infinite programming (SIP) within a general optimization framework. The ITSSP has an infinite number of constraints because it uses functional intervals with time (t) being an independent variable. The different t values within the range [0, 90] lead to different constraints. At same time, ITSSP also includes probability distribution information. The ITSSP method can incorporate pre-defined water resource management policies directly into its optimization process to analyze various policy scenarios having different economic penalties when the promised amounts are not delivered. The model is applied to a water resource management system with three users and four periods (corresponding to winter, spring, summer and fall, respectively). Solutions of the ITSSP model provide desired water allocation patterns, which maximize both the system’s benefits and feasibility. The results indicate that reasonable interval solutions were generated for objective function values and decision variables, thus a number of decision alternatives can be generated under different levels of stream flow. The obtained solutions are useful for decision makers to obtain insight regarding the tradeoffs between environmental, economic and system reliability criteria.     

区域尺度地下水埋深与矿化度对土地盐碱化转变概率研究

为探明受地下水埋深与矿化度影响的极度干旱荒漠区土地盐碱化转变概率,选定甘肃省景泰川电力提灌灌区(简称"景电灌区")为研究区,分别利用ArcGIS空间插值中的反距离权重法、样条函数法、趋势面法及普通克里金法对2017年的地下水埋深和矿化度监测数据进行插值,结合误差矩阵选取最优插值方法,并对研究区1994、2008和2017年三期监测数据进行插值分析,再通过重分类消除量纲进行叠加,将土地盐碱化难易程度划分为5级,分析了研究区土地盐碱化转变概率。结果表明,地下水埋深和矿化度平均值在1994年至2017年间呈不断上升趋势,灌区土地盐碱化转变概率西南低东北高,地下水埋深较深区域不易形成盐碱地,地下水埋深较浅区域,矿化度越大越易形成盐碱地,研究可为干旱荒漠区区域地下水利用提供理论依据。     

改进AHP法灰色关联和模糊综合评价在地下水质评价中的适用性

以改进层次分析法(AHP)权重值研究为目的,通过对数据的标准规范化处理自行构造判断矩阵,采用MATLAB计算研究区地下水质的权重值,将所得权重值运用于灰色关联和模糊综合评价两种方法,以白城地区为例对地下水中铁、砷、氟等9项指标进行评价。结果表明:铁、钠、氯化物、硝酸盐(N)、硫酸盐、溶解性总固体、总硬度、砷、氟的权重分别为0.137、0.105、0.130、0.113、0.106、0.070、0.057、0.209、0.073。两种方法评价结果具有较高的空间一致性,白城地区水质总体较差,Ⅰ～Ⅴ类水占比分别为12%、13%、9%、14%、52%,西北部洮儿河扇形地区水质远优于东南部平原区。通过两种方法的适用性验证,表明改进的AHP法是符合实际的。     

水工结构可靠度设计的简化及条件概率的应用

水工结构可靠度设计采用的两种方法中,以概率极限状态为原则的分项系数法较经验安全系数法更为严谨,但分项系数较多,为此提出二系数设计法对其进行简化。此外,还提出用条件概率法解决可靠度分析中常遇到的一个试验得到两个相关试验值和现场子样容量较小两类问题。对以上问题用实例进行了说明。     

中国地下水资源质量评价(Ⅱ)——地下水水质现状和污染分析

对我国平原区浅层地下水水质现状进行了评价。初步评价结果表明,我国地下水水质形势严峻,劣质水分布面积占平原区面积近60%。高矿化度地下水分布比较广泛,总硬度和矿化度成为地下水主要的超标因子。铁、锰、氟等水文地球化学组分对地下水水质也有明显的影响,除天然因素外,地下水受人为污染的程度十分严重,全国有近25%平原区地下水受到不同程度的污染。在人口和社会经济活动密集的流域,地下水污染已经呈现大范围扩散的态势。地下水保护形势十分迫切,指出要客观认识到地下水水质的先天因素和人为污染的区别,有针对性地进行地下水的保护。     

重力坝失稳破坏变形表征指标警戒值的拟定

抗滑稳定是重力坝设计与运行中关注的最基本要求,其宏观层面一定程度上可表征为重力坝变形性状的转异行为。大坝变形安全警戒值的确定,传统上多基于各种确定的结构参数和数学模型,缺乏对相关影响因素不确定性的考虑。因此,从不确定性分析理论入手,在对重力坝抗滑稳定可靠指标、变形与坝前水深相关性剖析的基础上,引入响应面法,通过对大坝变形水压分量与抗滑稳定可靠指标之间函数关系的合理拟合,依据现行可靠性设计规范,提出了一种基于抗滑稳定可靠指标的重力坝变形安全警戒值拟定方法,并进行了实际工程案例验证。通过与传统典型小概率法拟定结果的比较,得出了总体合理、可行的结论。文中方法是传统方法的有益补充,可作为传统方法计算结果的有效验证手段。     

基于支持向量机的重要抽样方法

在结构可靠度分析中,对于非线性的隐式极限状态方程,与一次二阶矩方法相结合的传统响应面方法一般并不适用。支持向量机算法较好地解决了小样本的统计学习问题,为解决有限样本情况下结构极限状态功能函数的重构提供了有力的理论基础。基于回归支持向量机方法,采用有限的经验点重构结构极限状态方程,结合重要抽样方法计算非线性的隐式极限状态方程结构的可靠度。该方法相对传统响应面方法在结构计算工作不增加的条件下,可以获得高精度的解,能较有效地解决非线性的隐式极限状态方程的结构可靠分析问题。     

考虑参数空间变异的高风化岩质边坡可靠性分析

为探讨高风化岩质边坡参数的内在变异性,结合一阶可靠性理论(FORM)、改进拉丁超重要立方采样法(LHIS)的数值分析方法,对实际工程中的高风化岩质边坡进行概率稳定性分析。充分考虑高风化岩质边坡的岩石参数的空间变异性对边坡稳定性的影响,利用LHIS模拟计算得到安全系数的概率分布,同时利用FORM确定临界失稳破坏面的概率进行初步的敏感性分析,从而确定模型输入参数对边坡稳定性的影响;利用Spencer极限平衡法求出失稳破坏面的F_s来评价功能函数G(X)的值,并计算可靠性指标。结果表明:考虑岩石参数的空间变异性比传统单一变量更能真实反映高风化岩质边坡的特征;利用LHIS能比传统的抽样方法明显减少模拟次数,提高效率;可靠性理论及概率稳定性分析方法比传统的极限平衡法更适用于评价岩土参数空间变异的高风化岩质边坡的安全性。     

湖区地层垂向渗透系数概率分布特征分析

为了确定某湖区湖水与地下水的交换水量,根据湖底地层渗透系数的野外现场测定值,用适线法和蒙特卡罗法对研究区地层垂向渗透系数的概率分布进行拟合,在此基础上,分析了渗透系数试验测定值的可靠性.结果表明:与正态分布和均匀分布相比较,湖底地层垂向渗透系数概率分布较接近对数正态分布;渗透系数超过测定均值的概率在30%以上.     

Groundwater Exploitation and Its Impact on the Environment in the North China Plain

Abstract

The North China Plain (NCP) is one of China's most important social, economic, and agricultural regions. Currently, the Plain has 17,950 thousand ha of cultivated land, 71.1 percent of which is irrigated, consuming more than 70 percent of the total water supply. Increasing water demands associated with rapid urban and industrial development and expansion of irrigated land have led to overexploitation of both surface and the ratio of groundwater resources, particularly north of the Yellow River. In 1993, the ratio of groundwater exploitation to recharge in many parts of the NCP exceeded 1.0; in some areas, the ratio exceeded 1.5. Consequently, about 1.06 million ha of water-short irrigated areas in the NCP also have poor water quality. Persistent groundwater overexploitation in the northern parts of the NCP has resulted in water-level declines in both shallow and deep aquifers. According to data from 600 shallow groundwater observation wells in the Hebei Plain, the average depth to water increased from 7.23 m in 1983 to 11.52 m in 1993, indicating an average water-table decline of 0.425 m/year. Water table declines are not uniformly distributed throughout the area. Depletion rates are generally greatest beneath cities and intensively groundwater-irrigated areas. Water-table declines have also varied over time. With the continued decline of groundwater levels, large depression cones have formed both in unconfined and confined aquifers beneath the Hebei Plain. Groundwater depletion in the NCP has severely impacted the environment. Large tracts of land that overlie cones of depression have subsided, seawater has intruded into previously freshwater aquifers in coastal plains, and ground-water quality has deteriorated due to salinization, seawater intrusion, and untreated urban and industrial wastewater discharge. In order to balance groundwater exploitation with recharge, the major remedial measures suggested are to strengthen groundwater management, to raise water use efficiency, to adjust the water-consumed structure, and to increase water supply     

基于极限学习机的边坡可靠度分析

对于边坡极限状态函数无法显式表达的情况,传统可靠度分析方法存在求解困难或计算量大的弊端。提出了一种基于FLAC^3D和极限学习机的边坡可靠度分析方法。利用均匀试验设计构造随机变量样本,基于FLAC^3D强度折减法计算随机变量样本对应的安全系数;通过极限学习机强大的数据拟合能力映射出安全系数与随机变量之间的关系,构造响应面功能函数;将蒙特卡罗模拟生成的大量随机数代入响应面获得安全系数,在此基础上,计算边坡的失效概率与可靠度指标。通过具体算例分析,并与其他方法对比,发现本文方法结果可靠、易于实现,为边坡可靠度分析提供了一种新途径,具有广泛的应用前景。