Control of Seepage through Earth Dams Based on Pervious Foundation Using Toe Drainage Systems

Many dangerous effects arise from seepage through earth dams based on pervious layer. Therefore, the dam embankment must be provided with seepage control measures to avoid such effects. In the present work, different control methods were used such as flat slopes, toe drainage systems, and a catch drain in the tail water. The hydraulic performance of each control measure was evaluated using the analytical solutions, previously developed, to estimate the seepage quantity (q), the height of seepage surface (h3), and the coordinates of the free surface (hx). Study was conducted on a physical model for a dam embankment having a top width (b) = 10.0 meter, height (Hd) = 30.0 meter, and slope factor (m) = 1.5. The obtained results were analyzed and presented in dimensionless charts. Results showed that, the used control measures possess a great effect on the characteristics of seepage through earth dams based on pervious foundations. A comparative study was conducted between the studied toe drainage systems to enable the designers the better choice for design purposes.

Hydrological Process Analysis in Earth Dams Using the PCSiWaPro as a Basis for Stability Analysis

Earth dam is always a safety issue, as it can experience catastrophic destruction due to the slope failure caused by various factors, such as water content increasing in earth slopes, vegetation root decay and so on. This study is to investigate the variation of hydrological processes in the saturated and partially saturated slopes with a new simulation program PCSiWaPro （a computer aided leachate forecast tool） under transient boundary conditions. The integration of a weather generator inside the PCSiWaPro allows a transient water flow calculation with respect to atmospheric conditions （precipitation, daily mean temperature and sunshine duration） and removal of water by plant roots and leaves. The simulation results of one scenario in a Chinese earth dam clearly demonstrate a good applicability of the program PC S iWaPro.

Monitoring models for base flow effect and daily variation of dam seepage elements considering time lag effect

Affected by external environmental factors and evolution of dam performance, dam seepage behavior shows nonlinear time-varying characteristics. In this study, to predict and evaluate the long-term development trend and short-term fluctuation of the dam seepage behavior, two monitoring models were developed, one for the base flow effect and one for daily variation of dam seepage elements. In the first model, to avoid the influence of the time lag effect on the evaluation of seepage variation with the time effect component of seepage elements, the base values of the seepage element and the reservoir water level were extracted using the wavelet multi-resolution analysis method, and the time effect component was separated by the established base flow effect monitoring model. For the development of the daily variation monitoring model for dam seepage elements, all the previous factors, of which the measured time series prior to the dam seepage element monitoring time may have certain influence on the monitored results, were considered. Those factors that were positively correlated with the analyzed seepage element were initially considered to be the support vector machine(SVM) model input factors, and then the SVM kernel function-based sensitivity analysis was performed to optimize the input factor set and establish the optimized daily variation SVM model. The efficiency and rationality of the two models were verified by case studies of the water level of two piezometric tubes buried under the slope of a concrete gravity dam.Sensitivity analysis of the optimized SVM model shows that the influences of the daily variation of the upstream reservoir water level and rainfall on the daily variation of piezometric tube water level are processes subject to normal distribution.

Seepage safety monitoring model for an earth rock dam under influence of high-impact typhoons based on particle swarm optimization algorithm

Extreme hydrological events induced by typhoons in reservoir areas have presented severe challenges to the safe operation of hydraulic structures. Based on analysis of the seepage characteristics of an earth rock dam, a novel seepage safety monitoring model was constructed in this study. The nonlinear influence processes of the antecedent reservoir water level and rainfall were assumed to follow normal distributions. The particle swarm optimization （PSO） algorithm was used to optimize the model parameters so as to raise the fitting accuracy. In addition, a mutation factor was introduced to simulate the sudden increase in the piezometric level induced by short-duration heavy rainfall and the possible historical extreme reservoir water level during a typhoon. In order to verify the efficacy of this model, the earth rock dam of the Siminghu Reservoir was used as an example. The piezometric level at the SW1-2 measuring point during Typhoon Fitow in 2013 was fitted with the present model, and a corresponding theoretical expression was established. Comparison of fitting results of the piezometric level obtained from the present statistical model and traditional statistical model with monitored values during the typhoon shows that the present model has a higher fitting accuracy and can simulate the uprush feature of the seepage pressure during the typhoon perfectly.

Analysis and evaluation on seepage stability of Hongxing reservoir dam,Heilongjiang

Hongxing reservoir was constructed on the floodplain of Hulan River in Heilongjiang. The geological problem of the reservoir is the seepage of the dam base and its related seepage stability. The leakage of the reservoir is caused by the water head differences between the upstream and downstream of the dam. Severe seepage could decrease the engineering benefits of the reservoir. Moreover,infiltration function of water will influence the safety of the dam. Through the analysis on the granule constitute and the formation of the dam base,the types of the seepage failure apt to happen were defined and the anti-infiltration and the permissible depression ratio were determined. Using the numerical simulation software GMS,the two-dimension numerical modeling has been carried out to analyze the seepage field of the reservoir. Through the two conditions modeling with concrete impervious wall and no concrete impervious wall,the largest flow rate,single-wide seepage discharge and the max infiltration gradient of the dam base were calculated. According to the permeable depression ratio of the dam base,the seepage stability of Hongxing reservoir dam base was analyzed.

Overtopping breaching of cohesive homogeneous earth dam with different cohesive strength

In consideration of the range of clay content of Chinese earth dams, the world's highest prototype tests have been made to research on the effects of cohesive strength of filling of cohesive homogeneous earth dam on breach formation. Three breach mechanisms were presented, they were the source-tracing erosion of dam body with the form of "multilevel headcut", "two-helix flow" erosion of dam crest and collapse of breach sidewalls due to instability. It can be concluded that the cohesive strength of filling of earth dam has great effect on breach formation. When the cohesive strength is bigger, the breach process becomes slower, and the peak outflow and the final width and depth of breach become smaller. The main character of the breach formation is head cutting and dumping collapse. When the cohesive strength is smaller, the breach process becomes faster, and the peak outflow, the final width and depth of breach become bigger. The main character of the breach formation is single level head cutting and shearing collapse.

Seepage simulation of high concrete-faced rockfill dams based on generalized equivalent continuum model

This research focused on the three-dimensional(3 D) seepage field simulation of a high concrete-faced rockfill dam(CFRD) under complex hydraulic conditions. A generalized equivalent continuum model of fractured rock mass was used for equivalent continuous seepage field analysis based on the improved node virtual flow method. Using a high CFRD as an example, the generalized equivalent continuum range was determined, and a finite element model was established based on the terrain and geological conditions, as well as structural face characteristics of the dam area. The equivalent seepage coefficients of different material zones or positions in the dam foundation were calculated with the Snow model or inverse analysis. Then, the 3 D seepage field in the dam area was calculated under the normal water storage conditions, and the corresponding water head distribution, seepage flow, seepage gradient, and seepage characteristics in the dam area were analyzed. The results show that the generalized equivalent continuum model can effectively simulate overall seepage patterns of the CFRD under complex hydraulic conditions and provide a reference for seepage analysis of similar CFRDs.

基于RUN-XGBoost算法的土石坝渗流预测模型

针对传统土石坝渗流预测模型存在局部最优、抗干扰性差和预测精度低等问题,通过RUN算法优化XGBoost算法得到RUN-XGBoost算法,构建了RUN-XGBoost模型以获得更优的土石坝渗流预测结果。该模型在种群初始化时采用RUN算法对XGBoost算法的3个主要参数进行改进,使预测结果有较高的有效性;通过自动寻找最优参数增进算法的整体收敛速度和预测精度,同时引入随机解,使算法能够排除局部最小值并继续搜索,从而获得全局最优结果。工程实例验证结果表明,RUN-XGBoost模型具有简洁、高效、预测精度高、鲁棒性强等优点。

无单元Galerkin法的电流场与渗流场耦合正演

联合求解渗流场与电流场是确定土石坝渗流精确分布及评价渗流严重程度的重要途径.为解决水文-地球物理方法中存在的渗-电拟合度差及分辨率损失严重等问题,针对电性参数对水文状态变量的敏感性,本文开发一种基于无单元Galerkin法(Element-Free Galerkin Method,EFGM)的渗流场与电流场耦合正演算法.一方面,通过引入岩石物理关系经验公式及水文状态变量构建耦合模型;另一方面,通过滑动最小二乘法构造形函数,利用罚函数计算边界条件,以解决耦合模型的构建过程中对网格单元过度依赖问题来提高渗-电拟合精度.数值模拟的渗-电关联响应及耦合正演中,分析了土石坝内电流场及渗流路径,探索了各分量对土石坝不同附属结构体的异常响应特征.关联响应结果显示,饱和区内渗-电关联响应吻合较好.但由于非饱和渗流的特殊性,非饱和区介质岩石的物理特性会随着饱和度、孔隙度等因素的变化而发生改变,从而导致土石坝内非饱和区物性参数的分布与饱和区不同,从而造成非饱和区内渗-电场关联响应存在差异.在非饱和区域,耦合电位及电流密度分布与渗流分布吻合度高.渗-电耦合结果对实施模型约束的水文-地球物理耦合反演具有重要理论和实际意义.

均质土坝管涌溃决实验渗流分析

管涌渗漏破坏是导致土石坝溃决的主要原因之一,通过模型实验开展土石坝管涌过程渗流场变化研究,对土石坝安全预测预警具有重要意义。采用预设管涌通道模拟管涌渗漏的方式,建立了室内小尺寸均质土坝管涌溃决模型;通过布置小量程渗压计,获取土坝模型的渗流场数据,对土坝模型从蓄水到渗透破坏再到溃决全过程的渗流场变化进行了深入分析研究。分析发现,在蓄水阶段,相同轴距的管涌断面测点渗流压力小于非管涌断面测点的测值,但测值达到峰值的时间早于非管涌断面测点;在溃决阶段(出现明流和形成溃口阶段),坝体内渗流压力出现骤降,且越靠近管涌断面渗流压力骤降时间越早、骤降幅度也越大。该认识,对于土石坝管涌渗漏破坏预测预警提供借鉴。

基于最弱t-norm算法模糊贝叶斯网络土石坝渗漏风险分析

针对土石坝工程渗漏影响要素多,风险评估体系不完善的问题,提出一种基于最弱t-norm算法模糊贝叶斯网络的土石坝渗漏风险分析模型。首先基于土石坝渗漏破坏成因构建土石坝渗漏风险分析网络,再基于层次分析法和最弱t-norm聚合算法求解不同专家判断的相似性结果,最后将相似性结果转化为概率后代入贝叶斯理论计算水库渗漏破坏风险。以2005年英德尔水库渗漏破坏事件为例,计算得到该库渗漏破坏概率为0.08,属于不可接受风险,并通过反向诊断验证了该模型的可靠性与灵敏性优于传统算法。研究结果可为土石坝渗流风险分析与处置决策提供参考。

黄土丘陵山区坝前淤积土固结渗透试验及其预测模型

为研究宁夏南部山区坝前淤积土非线性渗透特性,以宁夏南部黄土丘陵山区小型水库除险加固中“坝前淤积面加坝”技术为工程背景,通过固结渗透试验获得了50、100、150 cm深度原状淤积土施加25、50、100、200、400、800 kPa压力下的竖向变形量及渗透系数。针对宁夏南部山区水库坝前淤积土的特性,在分析常见非线性渗透模型基础上,利用皮尔逊相关性和灰色关联度分析方法,计算渗透系数与不同形式孔隙比之间的相关性,给出符合本地区坝前淤积土的双对数非线性渗透模型。结果表明:渗透系数与400 kPa固结压力下孔隙比的皮尔逊相关系数和灰色关联系数分别为0.968、0.893,二者相关性显著性较高,而且均高于其他形式孔隙比的相关系数;拟合的双对数非线性渗透模型的决定系数R~2在0.93以上,较好反映了宁夏南部山区坝前淤积土渗透特性,弥补了单指数渗透模型预测精度不足和参数复杂的缺陷;建立的固结-渗透系数表达式,为坝前淤积土大变形非线性排水固结研究奠定了基础。

基于多指标融合的土石坝渗流性态监控与分级预警研究

渗流是反映土石坝运行安全的重要效应量。为服务某土石坝渗流安全监控和预警需求,基于大坝渗压原型监测资料,分别采用置信区间法和典型小概率法拟定大坝渗压水位数学模型监控指标;采用地勘和反演方法确定渗透系数,建立大坝典型断面有限元模型并开展渗流分析计算,拟定大坝渗压水位结构分析监控指标;在此基础上,融合数学模型和结构分析法渗压水位监控指标并进行验证对比,探究并构建了“数据-机理”驱动的大坝渗流性态监控与分级预警方法。经实例分析,验证了提出方法的有效性,以期为大坝渗流监控和工程安全服役提供有效支撑。

小型土石坝水库除险加固及渗流安全稳定评价

水利除险加固对于早期建设的许多病险水库安全运行至关重要。沙表北水库建成年代早,影响水库安全稳定的工程地质条件复杂,同时坝体存在安全稳定隐患,有渗流安全隐患。以沙表北水库为研究背景,从坝顶加固、防渗加固和坝坡加固提出系统加固方案,针对大坝渗流和安全稳定进行复核分析,提出合理的监测补充措施。

基于EEMD-WOA-SVM的土石坝渗流量预测

为准确预报土石坝渗流量的变化趋势,针对传统的时间序列模型存在非线性处理能力较差、捕捉序列依赖关系能力不足等问题,建立了基于EEMD-WOA-SVM的土石坝渗流量预测模型.该模型采用集合经验模态(EEMD)有效分解土石坝渗流时间序列,引入鲸鱼优化算法(WOA)寻找支持向量机模型(SVM)的最优超参数组合,再将各模态分解分量代入组合模型预测并重构预测结果.案例分析结果表明,所建EEMD-WOA-SVM模型与传统的SVM模型相比,其拟合优度R2提升了19.8%,均方误差EMS、均方根误差ERMS、平均绝对误差EMA和平均绝对百分比误差EMAP分别降低了76%、50.3%、45.2%和43.2%.另外,与GA-SVM和WOA-SVM模型相比,R2值达0.9486,EMS、ERMS、EMA和EMAP分别降低至0.0012、0.0352、0.0289和0.0176,进一步说明了该组合模型具有较高的预测精度,为土石坝渗流量的精确预测提供了新途径.

组合防渗方案对土石坝稳定的影响研究

以某粉质粘土心墙土石坝为研究对象,运用Geo-studio有限元软件建立坝体二维模型,研究组合防渗方案对土石坝稳定性的影响。采用Geo-studio数值模拟的方法,比较不同长度水平黏土铺盖、不同深度垂直混凝土防渗墙和组合防渗方案的渗流流量、水力坡降变化情况,评估其在实际工程中的效果。结果表明,组合防渗方案能降低坝体渗流流量、水力坡降,有效提高土石坝的稳定性,对于保障水库安全具有重要意义。

复合土工膜防渗斜墙在碾压土石坝工程中的应用与质量控制

碾压土石坝因其技术简单、取材方便等特点,常作为矿山开采水利工程设施的流行坝型,为避免因有色金属渗漏而导致水源污染和生态破坏的潜在风险,采取有效的防渗措施对水坝的设计与施工至关重要。旨在探讨复合土工膜防渗斜墙解决方案,通过多层次结构的组合,包括长丝无纺土工布、双糙面HDPE膜、钠基膨润土毯等,形成可靠的防渗屏障,锚固于坝脚30 m外的截渗齿槽中,通过与土体的紧密结合,成功构建有效的防渗系统,以期为类似矿山建设水利工程设施的设计与施工提供有益的经验借鉴。

桑涧水库大坝渗流数值模拟分析

文章以桑涧水库为例,由于测压管数据失真严重,利用Autobank设计软件对土石坝进行渗流稳定数值模拟分析计算,结果表明与大坝现状渗流异常现象相吻合,为解决大坝类似工程问题提供参考,也为大坝防渗加固提供依据。

基于VBA语言的土石坝理正渗流分析输入文件自动生成

在土石坝安全评价与除险加固过程中,渗流分析计算是其中的一项重要工作。利用VBA计算机语言自动生成理正岩土渗流分析的输入文件,可以实现土石坝渗流的批量计算,对于土石坝多断面、多工况的渗流分析能够大大提高计算效率,实现了土石坝渗流分析的标准化工作,极大地提高了土石坝渗流分析的效率和成果质量。

渗流作用下均质土坝温度场变化规律试验与数值模拟研究

土质堤坝是保障中国经济和社会发展的重要基础设施,而渗透破坏是导致堤坝失事的主要原因。监测渗流尤为关键,渗流热监测技术无污染,价格低廉,测量精度高,近年来发展迅速。笔者采用物理模型试验与数值模拟的方法,对渗流作用条件下有无渗漏通道情况的堤坝温度场的变化规律进行了研究,证实了坝体渗漏对温度场分布的影响。通过试验实测数据验证堤坝渗流场与温度场耦合模型的准确性,为渗流热监测技术的进一步研发提供理论支撑。