复合防渗衬垫缺陷渗漏量计算方法探讨

复合衬垫系统的渗漏量是评价衬垫系统的一个重要指标,笔者假定膨润土中流线垂直向下和不考虑土工膜与土工织物之间空隙的影响,根据水流的连续条件,利用解析的方法,对土工膜上存在孔洞缺陷的土工膜＋GCL复合衬垫系统的缺陷渗漏量进行数值模拟。然后通过试验验证,得出该计算模型可以作为存在孔洞缺陷的土工膜＋GCL复合衬垫系统渗漏量的一个计算手段。     

土工膜缺陷对土石坝渗流特性的影响及控制措施

由于土工膜因缺陷导致的渗漏问题可能对土工膜防渗土石坝工程安全造成隐患,为此模拟不同的土工膜缺陷大小和位置,分别采用剔除单元法和渗透系数放大法对存在缺陷的土工膜坝面防渗土石坝进行饱和-非饱和三维渗流场有限元数值仿真计算,分析土工膜不同缺陷条件下大坝整体及局部渗流场变化规律。计算结果表明:土工膜缺陷渗漏仅对缺陷附近坝体局部渗流场分布产生较大影响,对大坝其他部位影响不大;土工膜缺陷位置越低,缺陷处水头越大,缺陷渗漏量增加越明显,并使缺陷处膜后坝体浸润线局部抬高。最后,针对土工膜缺陷渗漏提出了若干工程设计控制措施。     

随机多缺陷条件下土工膜防渗土石坝渗漏特性

由于土工膜缺陷渗漏可能对土工膜防渗土石坝的防渗安全性造成隐患,采用饱和-非饱和渗流有限元理论,对坝面防渗土工膜多缺陷随机分布下的典型土石坝进行三维渗流场有限元模拟,合理考虑土工膜缺陷的数量、类型、位置、大小及其分布,重点分析土工膜的渗透量和缺陷渗漏量及膜后浸润面的变化规律。结果表明:与单缺陷条件下大坝渗流特性相比,坝面完好部分土工膜的渗透量变化不大,但多缺陷引起的渗漏量明显增大,导致大坝的总渗流量大幅增加。多缺陷会引起膜后坝体浸润面整体抬升,但局部浸润面高度变化与缺陷位置和数量明显相关,所在剖面缺陷位置越低,数量越多,浸润面抬升越明显。另外,膜后垫层水头局部分布规律与相邻缺陷渗漏的交叉效应相关。     

平原水库土工膜防渗特性分析

复合土工膜防渗措施是解决平原水库渗漏问题的有效手段。为了研究平原水库土工膜防渗特性,以山东省清源湖水库为例,采用数值模拟与现场实测相结合的方法,建立了基于饱和-非饱和渗流微分方程的土工膜防渗围坝渗流有限元分析模型,并将计算结果与实测数据进行了对比。研究表明铺设土工膜防渗后,非饱和区域显著增加,忽略非饱和区域会使得渗漏量计算值偏小、浸润线及溢出点高度计算值偏低,令设计者低估渗漏的严重程度,不利于坝体的渗流稳定;土工膜缺陷因素(如缺陷的位置、尺寸、数目及与其下垫层的接触情况)对渗漏量和围坝浸润线亦有较大影响;土工膜缺陷及土工膜与下垫层的接触情况主要取决于施工质量,在施工期对土工膜缺陷进行严格控制,可有效减少渗漏量,对平原水库的安全运行具有十分重要的意义。     

土石坝防渗(复合)土工膜缺陷及其渗漏问题研究进展

在国内外众多土石坝采用(复合)土工膜防渗的工程背景下,分析了坝面或坝内土工膜缺陷的类型及产生缺陷的原因。归纳总结了国内外已有(复合)土工膜缺陷渗漏问题的研究成果,认为现有研究成果不适用于解决高土石坝复合土工膜的缺陷渗漏问题。同时认为高土石坝复合土工膜的缺陷演化规律、缺陷渗漏对坝体渗流场分布及对大坝安全的影响,以及如何采取有效的限渗减漏措施预防和减小缺陷渗漏量,已成为高土石坝复合土工膜防渗工程发展的瓶颈。为此,建议对复合土工膜的缺陷渗流特性进行试验研究,同时采用理论分析、数值模拟和工程实例反馈分析等手段对土石坝中复合土工膜的缺陷渗流及缺陷演化等相关问题进行系统研究,以便为复合土工膜防渗高土石坝的渗漏安全评判、预防及修复等方面起到理论指导作用。     

土工膜防渗低水头平原水库渗流场及膜体稳定性

针对平原水库土工膜稳定及渗漏等问题,结合珠江三角洲某土工膜防渗平原水库实际工程,建立渗流有限元模型,模拟施工和运行过程中土工膜破损和缺陷情况,分析土工膜缺陷对库底土工膜膜体稳定性和渗漏量的影响。结果表明:平原水库库内未储水时,土工膜缺陷对平原水库渗流场和库底土工膜稳定性的影响甚微;当库内及外江水位均处于高水位时,缺陷处膜下压力水头最大,但土工膜仍可维持稳定;当土工膜缺陷距离排水盲管30m,且缺陷孔径为0.5~3.0cm时,孔径变化对缺陷处渗漏量的影响较小,但缺陷数量和位置对缺陷处总渗漏量影响显著。     

土工膜防渗土石坝渗流特性分析

土工膜是一种新型防渗材料,在土石坝中已经得到了广泛的应用,但关于土工膜的渗流特性及防渗效果的研究还较少。基于土工膜的渗流机理,将发生在土工膜中的渗流分为土工膜本身渗透和土工膜缺陷渗漏两类,分别研究了影响土工膜渗透和渗漏的各种因素,总结了相应的工程措施,为土工膜的防渗设计提供依据。研究表明,精心的设计和高质量的施工是土工膜防渗工程成功的保证。最后介绍了电学渗漏位置探测法的原理及其在土工膜缺陷检测中的作用。     

仁宗海水库电站防渗系统设计及三维渗流计算

仁宗海水库电站堆石坝建于复杂深厚覆盖层上,防渗系统由土工膜面板+河床悬挂式防渗墙+两岸灌浆帷幕组成。为了验证设计防渗系统的合理性,采用饱和稳定渗流有限元法、渗流量插值网格法进行了三维渗流计算分析;同时采用二维有限元方法,就防渗系统不同部位存在缺陷对渗流场的影响进行了敏感性分析。计算成果表明,大坝渗流场分布符合一般规律,坝体和坝基发生渗透破坏的可能性很小,总渗漏量较小,设计的防渗系统是经济的、合理的、可靠的。建议加强防渗系统的施工质量控制,尤其应避免防渗系统浅表部缺陷。     

复合土工膜缺陷渗透量试验观测

结合某复合土工膜斜墙坝工程材料实际情况，自行设计试验装置，进行复合土工膜缺陷渗透量试验研究，经长期观测得到复合土工膜在不同缺陷孔径、不同水头作用下的缺陷渗透量实测值。分析了复合土工膜的缺陷渗透作用机理及相关因素对其影响，为土工膜的防渗设计提供依据。     

平原水库复合土工膜缺陷渗漏影响因素数值分析

使用Flac3d数值模拟软件,以南水北调东线大屯水库为原型,建立平原水库复合土工膜缺陷渗漏数值计算模型,分析缺陷孔径、位置、水头高度及多缺陷联合作用对平原水库实际工程渗漏量的影响。结果表明:数值计算结果和室内试验结果吻合度较高,可用于实际工况分析;复合土工膜缺陷的数量和水头高度是影响复合土工膜缺陷渗漏的主要因素,其次为缺陷尺寸、缺陷间距和缺陷位置;复合土工膜缺陷尺寸较小和距坝脚较远时对复合土工膜缺陷渗漏量影响较小;复合土工膜缺陷渗漏量随缺陷数量和库水位的增加呈线性增长的趋势,当缺陷距坝脚小于100 m,且缺陷尺寸大于10 mm,同时缺陷间距较小时,应重点排查修补。     

Development of Multiple Leakage Detection Method for a Reservoir Pipeline Valve System

The detection of multiple leakages in pipeline systems has been one of the challenging issues for the control of water loss in water distribution systems. Inverse transient analysis can be a useful principle for predicting leakage through the calibration of location and leakage quantity, based on the pressure reflection that originates from an abnormal boundary condition. In this study, an innovative leakage detection method is proposed to address unknown conditions on multiple leakage dimensions through introduction of revised leakage expressions based on a frequency domain approximation. A multiple leakage function was modified for an efficient representation of multiple abnormalities at a reservoir pipeline valve system. An iterative metaheuristic scheme (IMS) was designed to handle an optimization scheme for multiple leakages using a pressure response for a discharge impulse introduced through value manipulation. In order to address unsteady friction in hydraulic transients combined with multiple leakages, both one-dimensional and two-dimensional models were used to derive leakage expressions for turbulent and laminar flow conditions. An isolated multiple leakage function (IMLF) was proposed to exclusively encapsulate the impact of leakages and unsteady fiction. Considering uncertainties in the hydraulic transient propagation, data noise, and multiple local optima issues in large parameter calibrations, three advanced schemes were modularized to improve detectability of IMS. Several hypothetical examples were presented to show the potential of IMS, validity of three advanced schemes, and robustness in multiple leakage prediction compared to existing approaches.     

干旱区平原水库模拟蒸发量试验研究

干旱区平原水库水面蒸发是平原水库水量损失的重要组成部分,由于水库面积大,采用常规蒸发皿测定的蒸发量与水库实际蒸发量特征不相符。为了准确模拟干旱区平原水库蒸发量,开展了模拟水库的小面积水域蒸发试验,通过水位测针测量蒸发池的蒸发量,并与蒸发皿蒸发量进行比较。试验结果表明,在实际蒸发量中,蒸发池的蒸发量波动较大,蒸发皿蒸发速率比水面蒸发速率高9.1%。蒸发皿蒸发量与水面蒸发量的比值呈现先下降后上升的趋势;蒸发池水面蒸发量主要受到温度、净辐射、风速、饱和水汽压差影响;蒸发皿水体容量小,与蒸发池相比水体热容量较小,因此与大气交换更加快速,受净辐射和气温日较差影响较大。     

Groundwater Response to Tidal Fluctuation in an Inhomogeneous Coastal Aquifer-Aquitard System

This paper investigates tide-induced groundwater fluctuation and submarine groundwater discharge (SGD) in a leaky inhomogeneous coastal aquifer system with an upper unconfined aquifer, a lower confined aquifer, and an aquitard between them. The upper left aquifer is formed due to land reclamation. The SGD defined as the groundwater flow from land into the sea is controlled mainly by the hydraulic gradient between land and sea. An analytical expression is developed to discuss and assess the effect of inhomogeneity on the groundwater head fluctuation in the leaky aquifer system. Joint effects of aquifers’ parameters such as leakage and hydraulic diffusivity on the groundwater head fluctuation and SGD are investigated. The predicted results from the analytical expression indicate that the groundwater head fluctuation in both unconfined and confined aquifers is dependent on dimensionless leakages and increases with dimensionless hydraulic diffusivity.     

小浪底排沙洞无粘结预应力混凝土衬砌设计综述

小浪底排沙洞承担着水库排沙及泄洪任务，应用水头122m。为防止衬砌开裂，内水外渗，对山体稳定产生不利影响，原设计方案为有粘结预应力混凝土衬砌方案。在施工阶段，经专家论证和现场试验，决定改为无粘结预应力结构衬砌方案。文章详细介绍了无粘结预应力混凝土衬砌方案有关洞身衬砌的结构布置、预应力混凝土结构的应力特性、预应力构件及张拉设备的参数论证和选型等内容。     

高水头条件下氯离子击穿高岭土衬垫的离心模型试验研究

利用400 g-t土工离心机模拟了高水头条件下氯离子在高岭土衬垫中的一维运移及击穿过程。在1g条件下采用高含水率的高岭土泥浆加压固结制备形成衬垫模型,离心模型试验离心加速度50g,历时3 h 52 min,成功模拟了高水头条件下氯离子击穿黏土衬垫的过程。试验结果表明：离心状态下模型在高渗透压力作用发生再固结,在约30 min固结过程中模型发生了非稳定渗流,对早期污染物运移过程具有一定的影响,导致该运移过程与Ogata(1961)提出的污染物一维对流-扩散解析解的求解条件有所差异。采用等效时间的方法对试验结果进行拟合,根据拟合的参数预测原型的击穿时间,发现渗透系数为3.2×10^-9m/s的2 m厚黏土衬垫在上覆10 m水头作用下的击穿时间仅为1.97 a,稳定渗漏率为0.604 m/a。     

A Selective Literature Review on Leak Management Techniques for Water Distribution System

Water Distribution System suffers from leakages causing social and economic costs. There is need of platform to manage water distribution system more efficiently by detecting, localizing and controlling the leakages even before or as soon as they occur, ensuring quality water services to the consumers. Since last two decades, high efforts have been made by researchers for the development of efficient leakage management techniques for reduction of water losses in distribution system. This paper provides a comprehensive analysis on leakage management techniques covering three aspects: leakage assessment, leakage detection and leakage control, with an objective to identify present challenges and future scope in their respected field. Role of smart water technologies for efficient leakages management in pipeline network is also examined and discussed. Conclusion is drawn regarding current leakage management techniques and proposals for future work and existing challenges are also outlined.     

反拱水垫塘三维紊流场水力特性的试验研究

反拱底板水垫塘是一种新型的水垫塘型式,是一个倒拱形壳体结构。它是根据峡谷天然河道的形状,将水垫塘设计成中间低、两岸高的拱形体型,不同程度地利用拱的作用来抵抗巨大的动水压力,提高防护结构的安全性。随着反拱水垫塘的广泛应用,关于反拱水垫塘的水流场研究越来越受到重视。针对已建成的拉西瓦水电站的反拱水垫塘,根据重力相似准则,选择合适比尺1∶130,设计了反拱水垫塘水力学物理模型,模拟工况为设计水头7.69 cm,测量了在此工况下的反拱水垫塘各测点压强和流速值。通过对实验数据的处理得到原型反拱水垫塘的压强和速度值,实现了对高水头和大流量作用下反拱水垫塘底板动水压强及流速的试验研究,得出底板动水压强及流速沿流程以及沿拱圈横向的分布规律。     

Hybrid Leakage Management for Water Network Using PSF Algorithm and Soft Computing Techniques

Reduction of leakages in water distribution system (WDS) is one of the major concerns for water industries. This paper presents a hybrid leakage reduction model using pressure management technique, performed by optimizing water storage level in the tank, along with optimized control and localization of pressure reducing valve (PRV) in water distribution system. Pattern Sequence-based Forecasting (PSF) algorithm is used for prediction of flow rate (demand) from the tank for next 48 h, to calibrate the future desire water storage level in the tank. A mathematical tank and pump simulation algorithm is proposed for optimization of water storage level in the tank. A modified reference pressure algorithm is proposed for efficient localization of pressure reducing valve. Multiobjective genetic algorithm (NSGA-II) is used for finding out the optimized operational control setting of the pressure reducing valve for leakage minimization. The proposed algorithm leads to better leakage reduction of 20.81% in modified benchmark WDS, with a reduced number of the pressure reducing valves. Constraints such as maintaining lower hydraulic failure index (<0.01), emergency water storage, etc. is also considered. It can be concluded that the proposed hybrid leakage reduction technique provides efficient as well as cost-effective solution for leakage control.     

Experimental Evidence of Leaks in Elastic Pipes

Several studies have been carried out in recent decades to establish a relationship between total head and leaks. In literature, the leakage governing equations have been analysed in light of pipe materials, water head, leak dimension or shape. Most of these contributions questioned the classical Torricelli equation, demonstrating through experimental evidence that the classical orifice law can give unsatisfactory results. Nevertheless, starting from the Torricelli equation, other exponential or linear governing equations have been proposed as mathematical models able to reproduce the leakages in water distribution systems (WDSs). To investigate the validity of the proposed governing equations, an experimental campaign was carried out by means of a water distribution network composed of approximately 500 m of polyethylene pipes. The experiments were designed to investigate the effects of leak area and pipe rigidity on discharge. Furthermore, the effect of leak size enlargement with water head was analysed. Finally, the proposed research contributes to the population of a database for estimating the coefficients of head-discharge relationships.     

Pressure Zoning Approach for Leak Detection in Water Distribution Systems Based on a Multi Objective Ant Colony Optimization

Leakages result in considerable loss of water in water pipe networks. Therefore it is an important issue to detect leakage amount and its approximate location. Leakages in water distribution system are directly related to the operating pressure. In the current study, a new model is proposed for leakage amount and location detection and it is applied into two benchmark water distribution networks. In the proposed method, the water distribution networks are divided into three pressure zones in order to consider the leakage differences in different operating pressures. Then, nodal pressures and demands are calibrated using a new multi objective ant colony based optimization model. In this method, leaks are simulated as extra nodal demands. For determining the nodes where leakage happens, a probability based scheme is used. The leakage occurrence probability varies depending on the pressure zone that each node is located. The results illustrate the applicability of the proposed model for detecting the leakages in water distribution systems.