深厚覆盖层坝基防渗墙深度研究

在西部山区深厚覆盖层上建设高坝,坝基防渗是关系到工程成败的关键。塑性混凝土防渗墙加灌浆帷幕防渗体系已经在多座大坝工程中应用,实践证明是成功的。由于坝基防渗墙建设控制工期,并且工期较长,在满足防渗要求的条件下应尽量减少工程量。研究防渗墙的合理深度,能够在一定程度上减少工程量,优化施工工期。基于改进阻力系数法求得防渗墙底部坡降随防渗墙深度变化的解析解,并且通过数值模拟方法详细研究了深覆盖层内防渗墙深度变化时防渗墙底部水头、坡降的变化规律。认为深厚覆盖层内设置防渗墙的深度并非越深越好,而是存在一个最优深度。最优深度的取值取决于覆盖层的深度。一般情况下,相对深度比（防渗墙最优深度与覆盖层深度之比）在0.7左右为防渗的最优取值。     

新疆下坂地水库坝基防渗墙试验研究

新疆下坂地水利枢纽工程地处高寒、高海拔的山区,坝基覆盖层厚度达147.95m,透水性强,易坍塌和漏浆,块石坚硬,坝基防渗处理难度罕见。针对这一工程问题进行了坝基防渗墙试验研究,结果表明,以大深度混凝土防渗墙为主墙,下接帷幕灌浆的墙幕结合方案。本文针对新疆下坂地深厚覆盖层坝基防渗墙进行了试验研究,找出了防渗墙有效的施工深度及合理的施工方法,从而为坝基防渗墙设计施工提供了可靠的依据。     

深厚覆盖层上混凝土防渗墙的应力变形特性

建造在深厚覆盖层上的心墙坝,通常由土质心墙和其下部的防渗墙构成完整的防渗体系,防渗墙将受到水荷载和上覆坝体荷载的双重作用.本文采用三维非线性有限元分析了某心墙坝工程软弱覆盖层上两道混凝土防渗墙（第一道为嵌岩式,第二道为悬挂式）的应力变形特性并对其安全度评价方法进行了介绍.计算结果表明：①嵌岩式防渗墙和悬挂式防渗墙表现了不同的应力应变特性;②两道防渗墙的拉压应力均已超出混凝土的允许范围,建议采用高强低弹的混凝土配方.     

瀑布沟堆石坝防渗体自适应有限元分析

在深覆盖层地基上修建高土石坝,其防渗体系的可靠性是一项关键技术问题。针对瀑布沟水电站堆石坝的实际工程特点,应用自适应有限元方法,分析研究了大坝的稳定性和覆盖层中混凝土防渗墙与坝内黏土心墙接头部位的局部应力和变形情况,对比分析了不同接头形式的利弊,为设计部门推荐了合适的接头形式。     

深厚覆盖层上高土石坝极限抗震能力分析

针对强震区深厚覆盖层上高土石坝的特点,在三维真非线性有效应力地震反应分析基础上,提出了一套深厚覆盖层上高土石坝极限抗震能力的研究方法。从稳定、变形、防渗体安全等方面,对建在深厚覆盖层上的长河坝高心墙堆石坝的极限抗震能力进行了研究和分析。根据坝坡稳定性、地震残余变形、液化可能性、单元抗震安全性、防渗心墙及坝基防渗墙安全等多角度的评价结果,初步认为,长河坝的极限抗震能力为0.50～0.55g。     

高塑性黏土设置区域对土石坝混凝土结构应力变形影响

在土石坝混凝土结构周围设置一定范围的高塑土可以控制防渗墙改善应力集中、控制可能发生的裂缝。对设置不同高塑土区域心墙堆石坝进行有限元计算分析比较,结果表明,在廊道和主防渗墙顶局部设置高塑土,比沿心墙底部通长布置更能改善混凝土结构应力。心墙底高塑土区域设置过大,反而会使得原来局部设置高塑土分散的坝体荷载重新调整,从而导致廊道和主防渗墙的应力增加。     

对土坝劈裂灌浆设计与施工中几个问题的认识

水工建筑物的防渗一直是水利水电工程需要解决的重要课题之一。垂直防渗是防渗处理的主要手段,如水库大坝的垂直防渗心墙,在延长渗径、降低渗压水头方面,比水平防渗有效得多。由于具有机械化施工、不占用土地、管理和维护容易的特点,因而垂直防渗技术发展很快,运用很广。劈裂灌浆是在总结国内外土坝灌浆经验的基础上,在灌浆理论、机理和     

江雄水库坝基和坝肩渗漏分析与渗控方案评价

江雄水库施工中认为坝区存在较严重的渗漏问题, 由此, 在设计中对河床段坝基采用了上墙 (防渗墙) 下幕(帷幕灌浆) 组合防渗结构, 对两岸坝肩采用了帷幕灌浆防渗结构处理措施。利用渗流理论, 在分析坝区地质条件和概化水文地质模型的基础上, 建立了坝区三维渗流数值模型, 对坝区防渗处理设计条件下(方案Ⅰ和Ⅱ) 的坝基渗漏及渗透变形进行了计算和比较分析。结果表明, 两种防渗方案均可行, 但方案Ⅰ优于方案Ⅱ。     

超深覆盖层上高沥青心墙坝防渗墙受力状态的精细化分析EI北大核心

混凝土防渗墙是深厚覆盖层地基上修建土石坝的主要坝基防渗结构,是保证大坝安全的关键防线,因此,精细模拟防渗墙的受力状态,对于合理评价深厚覆盖层上土石坝工程具有重要意义。联合增量迭代法和有限元-比例边界有限元耦合方法,实现了土石坝应力变形的跨尺度精细化分析,克服了中点增量法求解局部强非线性问题时精度低的缺陷;发现了防渗墙-心墙接头附近和防渗墙底部土体剪切带的局部大应变特性,阐明了传统方法无法描述土体局部大应变而高估防渗墙应力的机制;提出了设置薄层单元来模拟应变局部效应的高效计算方法,实现了超深覆盖层上高沥青心墙坝防渗墙受力状态的三维精细化分析。本研究发展的有限元-比例边界元-增量迭代法-预设薄层单元的跨尺度非线性分析方法可为深厚覆盖层上土石坝防渗墙的安全评价和设计优化提供理论和技术支持。     

河谷地形对深覆盖层中防渗墙应力变形影响分析

为研究河谷地形对深厚覆盖层中防渗墙应力、变形的影响,以某沥青混凝土心墙堆石坝为工程背景,模拟了狭窄河谷和宽深河谷并分别建立有限元模型,坝体材料及覆盖层采用邓肯-张E-B模型,防渗墙与覆盖层、基岩之间的接触关系采用无厚度接触面模拟,进行三维非线性有限元计算,对比分析两种河谷情况下防渗墙的应力、变形情况。计算结果表明：狭窄河谷中,防渗墙沉降和水平向位移及防渗墙与覆盖层的不均匀变形均比宽深河谷小,其中不均匀变形最大减小了24.8%;宽深河谷中,防渗墙受河谷地形约束作用较弱,竖直向压应力较狭窄河谷更大,最大增加了40.3%;防渗墙的竖直向压应力最大值位置受中性点位置和河谷地形的共同影响,其中竖直向压应力最大值约30%来自墙顶坝体土压力,70%来自与覆盖层之间的负摩擦力。其研究结果可为不同地形条件下坝基防渗墙的设计提供参考。     

岩溶水库坝基防渗帷幕灌浆幕深与幕长的结构形式及处理

防渗帷幕灌浆是处理岩溶地区水库坝基坝肩渗漏的主要方法之一，它可以杜绝深、浅层的复杂的岩溶漏水问题，帷幕设计的合理性及其效果取决于水文地质、地下水的补排条件，水工建筑物结构之间的帷幕体的搭接形式，布置格局和边界范围。本文根据34处渗漏水库的灌浆实践，提出确定帷幕的深度和长度的原则，并得出了相关曲线和经验公式，对岩溶地区水库的渗漏处理进行探讨。     

Seepage problems in the right abutment of the Shahid Abbaspour dam, southern Iran

In this study, seepage phenomena through the right abutment of Shahid Abbaspour dam are investigated. The Shahid Abbaspour dam is a 200 m high arch dam, which regulates the waters of the Karun River, serves power generation, and flood control and irrigation needs. The dam site lies in the Zagros Mountains of southern Iran. This region presents continuous series of mainly of karstic limestone, marl, shale and gypsum ranging in age from Jurassic to Pliocene. The region has subsequently been folded and faulted. Seepage from the Shahid Abbaspour reservoir occurs mainly through the karstic limestone.The basic foundation treatment of the dam consisted of consolidation grouting, a high-pressure grout curtain and a drainage curtain. Moreover, a 144 m high and 30 m wide concrete cutoff wall was built to prevent reservoir seepage through a clay-filled fracture zone in the right abutment. The grout curtain penetrates the “Principal Vuggy Zone” only beneath the central portion of the dam and below the cutoff wall. In the right abutment fan curtains were constructed to reduce drainage flows, but the seepage problem could not be solved. In order to determine the seepage direction and karstification pattern, hydrogeological studies have been carried out. Additional investigation boreholes have been drilled to monitor fluctuations in groundwater level. Besides these, water chemistry, dye tracer, pinhole and XRF tests have been carried out. As a result of these studies, seepage paths have been identified in the karstic limestone in the right abutment of the dam.     

改进遗传算法在坝基帷幕灌浆方案优化中的应用

以一般基岩上的混凝土重力坝为例,采用改进的遗传算法对坝基有排水时的帷幕灌浆参数组合进行优化研究.根据帷幕的厚度进行单元网格剖分,用有限元数值方法计算渗流场,以坝基渗流量、坝基渗透压力和幕体本身的最大水力坡降不超过允许值为约束条件,以帷幕的工程造价最小为目标函数建立优化设计数学模型,寻找一般情况下的帷幕参数的最优组合,为工程设计提供参考依据.     

改进遗传算法在坝基帷幕灌浆方案优化中的应用

以一般基岩上的混凝土重力坝为例,采用改进的遗传算法对坝基有排水时的帷幕灌浆参数组合进行优化研究。根据帷幕的厚度进行单元网格剖分,用有限元数值方法计算渗流场,以坝基渗流量、坝基渗透压力和幕体本身的最大水力坡降不超过允许值为约束条件,以帷幕的工程造价最小为目标函数建立优化设计数学模型,寻找一般情况下的帷幕参数的最优组合,为工程设计提供参考依据。     

高密度电法在水库坝基无损检测中的应用

某坝基为砂卵石基础,其下为强风化基岩,坝基渗漏和左右岸绕坝渗漏是该水库坝基存在的主要地质问题。为此,采取了塑性混凝土防渗墙与双排帷幕灌浆相结合的综合防渗措施。为了检测水库坝基及塑性混凝土防渗墙施工质量,防止水库正常蓄水后发生渗漏,选用了高密度电法进行无损检测。工程采用温纳施伦贝尔法观测,分别采用5m和10m电极间距,电极数60个,剖面数16。依据5m和10m道距实测视电阻率剖面与反演结果的解释,对水库坝基和防渗墙的工程质量进行了评价,认为-25m桩号塑性混凝土防渗墙可能存在渗漏问题,-80m桩号对应一低阻异常,坝体可能存在渗漏通道;其余部位未发现明显异常。     

Using zero-thickness elements to simulate suspended cut-off walls in a regional seepage field

A regional seepage field is usually simulated by 2D horizontal seepage finite element method (FEM). However, the Dupuit assumption means that it does not take into account hydraulic head loss caused by vertical flow. In order to simulate a regional seepage field containing suspended cut-off walls by 2D horizontal FEM without any loss of accuracy and efficiency, a zero-thickness element is introduced. The zero-thickness element is used to model suspended cut-off walls and take into account the hydraulic head loss caused by vertical flow near the walls. The matrix equation is deduced. The deduction is based on the resistance coefficient method and the analytical solution of flow near suspended cut-off walls under plane condition. The accuracy of the method is assessed by comparing with 3D FEM results. These coincide with each other both in discharge and hydraulic head. The method is an effective way to simulate a suspended cut-off wall in a regional seepage field with 2D horizontal FEM.     

Optimization design and assessment of the effect of seepage control at reservoir sites under karst conditions: a case study in Anhui Province,China

Seepage analysis and assessment of the effect of seepage control at reservoir sites are essential parts of dam design and operations, and of considerable significance for the safe and economic design of the masses and hydraulic structures associated with reservoir sites. In this study, a systematic process is provided for the optimal design and assessment of seepage control of reservoir dams under karst development conditions. A reservoir dam planned for construction in the middle-upper reaches of the Huayang River in China is selected as a case example for illustration. A three-dimensional equivalent continuum seepage finite-element numerical model is applied to investigate the effectiveness of the proposed and optimized seepage-control schemes, and it is calibrated by an inversion analysis of the initial seepage field based on the flexible tolerance method and field penetration test data. By analyzing the sensitivity of seepage discharge to the length and depth of the grouting curtain, a safe and economic seepage-control optimization scheme is suggested. Additionally, the sensitivity of seepage discharge to the hydraulic conductivity of the limestone layer is analyzed, and the results show that the hydraulic conductivity of the limestone layer has a significant impact on the seepage discharge of the reservoir site. The methodology and results derived from this study can provide technical support and reference for the optimal design and assessment of seepage control for reservoir dam engineering under karst conditions.

     

Darcian flow under/through a leaky cutoff wall: Terzaghi–Anderson's seepage problem revisited

An analytical solution is obtained for 2‐D steady Darcian flow under and through a cutoff wall partially obstructing a homogeneous isotropic foundation of a dam. The wall is leaky; that is, flow across it depends on the ratio of hydraulic conductivity of the wall and the wall thickness that results in the third‐type (Robin) boundary condition along the wall, as compared with the Terzaghi problem for an impermeable wall. The Laplace equation for the hydraulic head is meshlessly solved in a non‐standard flow tube. A Fredholm equation of the second kind is obtained for the intensity of leakage across the wall. The equation is tackled numerically, by adjusted successive iterations. Flow characteristics (total Darcian discharge and its components through the wall and the window between the wall top and horizontal bedrock, stream function, head distribution, and Darcian velocity along the wall and tailwater bed) are obtained for various conductivity ratios, head drops across the structure, thicknesses of the foundation, and the degree of its blockage by the wall. Comparisons with the Terzaghi limit of an impermeable wall show that for common wall materials and thicknesses, the leakage may constitute tens of percent of the discharge under the dam. The through‐flow hydraulic gradients on a vertical wall face (Robin's boundary condition) as well as the exit gradients along a horizontal tailwater boundary (Dirichlet's boundary condition) acting for decades have deleterious impacts on dam stability because of potential heaving, piping, and mechanical–chemical suffusion. Copyright © 2017 John Wiley & Sons, Ltd.     

光照碾压混凝土大坝渗控分析

基于光照水电站坝基水文地质条件及坝体渗透特性的研究,建立了大坝三维有限元模型,模型较详细地考虑了坝体大坝不防渗结构和排水系统及坝基地质和防排渗结构。分析研究了薄层单元、排水孔幕的模拟方法,采用合适的方法计算了同条件下的渗控情况。通过综合对比分析,对该坝的渗流规律及相应渗控措施进行了初步地探讨。     

平原病险水库堤坝渗流控制方法研究

根据2000年实测数据绘制了在不同水位下水库堤坝测压管等水位线图,建立垂向二维有限元法渗流数值模型,模拟了尔王庄水库堤坝11个典型断面稳定渗流状态。综合分析测压管实测数据、现场勘查和计算结果,确定水库渗漏严重坝段。计算得出全封闭、悬挂式高压喷射灌浆防渗墙两加固方案下坝体单宽渗流量、浸润线、渗透比降等水力要素,结果表明全封闭设计可降低70.04%~98.32%渗流量,截渗沟或明渠处溢出渗透坡降降至0.001~0.023,控制效果显著。