Dynamic probability evaluation of safety levels of earth-rockfill dams using Bayesian approach

In order to accurately predict and control the aging process of dams, new information should be collected continuously to renew the quantitative evaluation of dam safety levels. Owing to the complex structural characteristics of dams, it is quite difficult to predict the time-varying factors affecting their safety levels. It is not feasible to employ dynamic reliability indices to evaluate the actual safety levels of dams. Based on the relevant regulations for dam safety classification in China, a dynamic probability description of dam safety levels was developed. Using the Bayesian approach and effective information mining, as well as real-time information, this study achieved more rational evaluation and prediction of dam safety levels. With the Bayesian expression of discrete stochastic variables, the a priori probabilities of the dam safety levels determined by experts were combined wfth the likelihood probability of the real-time check information, and the probability information for the evaluation of dam safety levels was renewed. The probability index was then applied to dam rehabilitation decision-making. This method helps reduce the difficulty and uncertainty of the evaluation of dam safety levels and complies with the current safe decision-making regulations for dams in China. It also enhances the application of current risk analysis methods for dam safety levels.

Safety evaluation of replacement reinforcement quality in abutment contact zones of ultra-high arch dam in first impoundment period based on prototype monitoring

Reinforcement quality evaluation at the abutment is an important research direction. Prototype monitoring and theoretical derivation were integrated to study the replacement reinforcement quality in abutment contact zones of the Xiaowan ultra-high arch dam. The principles of monitoring layout and design are introduced in detail. Prototype monitoring shows that the increment of the interfacial compressive stress is much larger in the impoundment stage than in the regulating stage. The water pressure and time-effect are two main factors affeeting the interfacial stress. The time-effect is the key factor in the initial impoundment stage, and the water pressure is the key factor after impoundment. The contact properties are significantly improved by grouting. This study shows that there are three typical stages in the joint opening hydrographs, namely the compression stage, opening stage, and stable stage. There is a nonlinear relationship between the joint opening and temperature, which can be well described by the S-function. In conclusion, the reinforcement effect is satisfying, and the abutment is safe.

Analysis of seismic disaster failure mechanism and dam-break simulation of high arch dam

Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code(3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, infl uence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far fi eld energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.

土石坝运行安全评价的改进组合赋权-云模型

针对土石坝运行安全评价中指标间相互影响、主客观权重赋值不够合理以及隶属区间模糊性等问题,提出了一种土石坝运行安全评价的改进组合赋权-云模型。以运行期土石坝为对象,构建了土石坝安全评价指标体系,分别采用G1法和改进熵权法对评价指标进行主客观赋权,融合博弈论思想求解最优权重组合系数,并引入云模型理论降低评价过程中隶属区间的模糊性。对某土石坝安全状态进行评价并与两种传统组合赋权法进行了对比,结果表明,3种评价方法的评价结果相近且与实际情况相符,但改进组合赋权-云模型考虑了评价指标间的关联性,运用博弈论思想使主客观权重赋值更加合理,能更客观地反映土石坝的真实运行状态。

三河口碾压混凝土高拱坝非线性超载安全度分析研究

三河口拱坝为国内已建的第二高碾压混凝土拱坝,其结构复杂,综合难度大。通过仿真计算分析非线性超载情况下三河口高拱坝安全度,进行综合技术评判,初步给出拱坝的安全度,与类似高拱坝工程进行对比分析,明确坝体应力状态及发展趋势,提出坝肩岩体的相对薄弱部位,并建议进行相应工程加固处理处理,保证拱坝结构安全运行,为类似工程设计提供非常有益参考。

基于改进随机森林的大坝监测数据质量评价算法

针对大坝安全监测数据质量评价效率低下、智慧化不足等难题,为了满足大坝高频率自动化采集的实时数据质量评价需要,从准确性、完整性、时效性和连续性4个方面出发提出了6项评价因子及由相关评价规范构成的安全监测历史数据质量评价标准,通过基于AUC值改进的随机森林算法建立了大坝安全监测历史数据质量评价算法,并将该算法应用于新疆柳树沟面板堆石坝多年安全监测历史数据评价。结果表明:通过AUC值改进的随机森林算法优于原始算法,在特征属性数量取3时效果最好,测试集的泛化误差最小仅为0.0195,平均准确率稳定在96.97%附近,10折交叉验证平均准确率达到97.77%,证明了该算法的可行性。

水库与水电站大坝安全评价体系对比研究

当前中国水库与水电站大坝采用不同的安全评价体系,为借鉴水电站大坝安全定检有关经验做法,查找水库大坝安全鉴定工作短板,主要从组织体系与技术体系两方面横向对比分析了水库与水电站大坝安全评价体系。水库与水电站大坝安全评价组织体系虽差别较大,但基本符合水利与能源系统大坝实际情况与特点;技术体系均以现场检查与监测资料分析为基础,分别按隐患类型、工程部位展开分项安全评价。建议从修订《水库大坝安全鉴定办法》、规范水库大坝安全监测工作、完善安全评价技术规范等方面进一步改进水库大坝安全鉴定工作。

槐树关水库大坝渗流安全评价与预测

为评价槐树关水库大坝的渗流稳定性,收集大坝近年来面板周边缝与坝基监测点处渗压计数据,库水位、气温、降雨量、坝后渗流的监测数据及大坝工程建设与地质资料,先将监测点处渗压计值和坝前水位进行Pearson相关性分析,再根据大坝工程建设及地质资料绘制大坝断面模型并导入Autobank7.7软件计算坝后渗流量,最后将气温、库水位、降雨量等影响因子代入PCA BP神经网络与随机森林、BP神经网络模型对坝后渗流量进行预测。结果表明:除P_(3)、P_(6)、P_(9)外的监测点渗压计值、坝后量水堰监测渗流量值与库水位相关性较强,符合大坝渗流场的一般规律,初步判定大坝较稳定;实际监测的坝后渗流量是Autobank软件模型理论计算值的8倍,判定大坝有出现渗流破坏的可能,后续应采取相应措施除险加固加强监测以保证大坝的稳定性;PCA BP神经网络与随机森林、BP神经网络3种模型最佳预测准确度分别为83.20%、79.35%、69.41%,其中PCA BP神经网络的预测效果最佳,通过模型预知渗流量防止渗流破坏对保证大坝的安全运行具有重要意义。

基于属性识别-组合赋权的大坝变形安全综合评价方法

针对大坝变形安全评价中的多属性有序分割问题,综合考虑最小代价原则、置信度准则与级别特征值,提出基于属性识别-组合赋权的大坝变形安全综合评价方法。根据大坝变形特点与成因,选取裂缝开合度、垂直位移和水平位移作为大坝变形的安全评价指标,运用K-S检验法确定评价指标数学分布,基于典型小概率法与3σ原则拟定安全监控指标,进一步应用层次分析法和熵权法分别确定评价指标的主客观权重,基于改进博弈论融合主客观权重,实现属性识别理论框架下的大坝变形安全综合评价。以工程实例检验该综合评价方法,并与工程实际情况、集对分析法进行对比,结果表明该方法具有较好的可行性与适用性。

Evaluating the safety of high arch dams with fractures based on numerical simulation and geomechanical model testing

It is important to estimate the probability of fracture extension and its impact on the safety of arch dams with fractures. Numerical simulation and geomechanical model test were combined to evaluate the overall stability and the extension probability of fractures. Numerical simulation forecasted the dam displacement and the operating behavior based on the parameters obtained from the back analysis. Geomechanical model test was based on small block masonry and the models with or without fractures were both tested. The results show that the deformation of dams is in line with general rules at a normal water load and the extension probability of the existing fractures is very small, which has no significant impact on the global stability of dams. Moreover, the failure process of arch dams with the existing fractures in dams at overload scenarios is similar to the one without the embedded fractures, i.e., the failure crack which is not caused by the existing fractures inside comes into being on the surface of dams itself.

下福水利枢纽混凝土重力坝工程地质安全评价

介绍了下福水利枢纽混凝土大坝及库区的主要工程地质条件,通过现状检查及变形监测资料分析,从工程地质角度对大坝、船闸、厂房等建筑物地基及边坡的运行现状进行了安全评价。

BBN水电站混凝土面板砂砾石坝渗流安全分析

采用GeoStudio岩土软件SEEP/W模块对BBN水电站混凝土面板砂砾石坝进行渗流稳定计算分析,计算正常蓄水位、设计洪水位、校核洪水位3个高水位工况下的渗透比降,与坝基岩土的允许渗流比降进行比较,并通过与渗流安全监测实测资料分析成果进行对比分析,评价坝体及坝基的渗流安全性态,同时复核渗流计算的合理性。研究成果可对类似混凝土面板砂砾石坝设计和安全评价中的渗流稳定计算和复核分析提供一定的参考。

基于TOPSIS与灰色关联法的水库大坝安全指数评价

对水库安全可靠性有影响的指标一般具有突出的层次性、不确定性等特征,根据各指标特征和相关标准选取6个维度19项评价指标,将水库安全评定结合TOPSIS和灰色关联法构建能够反映水库安全状态的指标体系。结果显示5座水库安全程度由高到低为六六庄水库、管楼水库、双岔口水库、沙子岗水库和二十亩地水库。此结果与专家评价基本一致,说明此方法的准确性和适用性;该模型可有效减小打分的主观性影响,评价结果更为科学,故其具有良好的应用前景,对实际工程具有指导意义。

大型水利工程安全鉴定现场检测的实践与评价

本文以国内大型的水利工程为实例,通过列举对混凝土结构、金属结构和地基与基础等方面进行安全评价时开展的现场检测关键项目,分析探讨检测对水利工程安全评价的重要作用,并指明安全鉴定应重点关注的检测项目类型,为科学客观评价大型水利工程的质量与安全提供重要参考依据。

基于改进AHP的可拓物元云模型的抽水蓄能电站下库大坝安全评价

随着抽水蓄能电站的不断发展,电站安全问题逐渐突出,针对某抽水蓄能电站下库区混凝土重力坝的安全状况进行安全评价分析。下库重力坝的安全评价问题,本质上是一个多因素影响问题。结合工程相关资料,筛选出评价指标,构建适用于抽水蓄能电站下坝址重力坝的安全评价体系,结合区间数理论及可拓物元思想,提出基于改进AHP的可拓物元云模型评价方法。选取某实际工程验证评价模型的有效性,结果表明,评价结果与大坝实际运行状况基本一致,研究结果可为大坝渗流安全评价提供参考。

东莞市三坑水库枢纽工程安全评价分析及处理建议

水库枢纽工程运行可靠与否直接关系到流域防洪、区域供水安全等问题。东莞市三坑水库枢纽工程由大坝、溢洪道和输水涵管3个部分组成,经多年运行后存在一定病险隐患。为保证枢纽工程防洪兴利效益的稳定发挥,有必要开展安全评价工作。对三坑水库各分项性能进行了复核评价,最终评价大坝安全性为二类坝。在安全评价基础上,提出了相关处理措施建议供主管部门采纳和决策。

运行期水电站大坝抗震安全评价实践与研究

大坝抗震安全评价须贯穿大坝设计、建设和运行的全生命周期。在运行期,由于大坝内外部条件的变化,需适时对大坝的抗震设防标准、抗震能力等进行复核与评价,保障大坝运行安全。通过对运行期水电站大坝抗震安全复核计算的开展情况进行统计分析,剖析了大坝安全定期检查中关于大坝抗震安全评价的实践经验。通过对运行期水电站大坝抗震安全复核计算结果进行量化分析,研究了大坝抗震能力随地震动参数变化的快速估算方法。上述研究成果对在大坝全生命周期中持续开展抗震安全评价具有一定的参考意义。

某水库混凝土重力坝渗流性态分析与评价

某水库建成运行多年,坝体出现不同程度的渗漏,需要进行大坝渗流安全分析评价。笔者通过对水库大坝坝基扬压力、渗流量监测资料进行分析,结合水库大坝运行表现,对大坝渗流安全进行分析评价。结果表明:坝体内部渗流通道复杂,防渗体系存在薄弱环节,坝体渗流量监测手段落后,监测精度和效率较低;水库大坝渗流性态不安全,建议进一步采取处理措施,及时消除隐患,确保大坝运行安全。

新疆某水库黏土心墙坝渗流稳定计算及安全评价分析

为评价新疆某水库工程的安全性,通过对坝体进行渗流稳定计算,分析不同工况下坝体渗流情况,并结合实际渗流监测数据分析坝体的稳定性。采用反演参数,确定更为合理的筑坝材料渗透系数,确保计算结果的准确性和可靠性。结果表明,该工程坝体渗流符合一般规律,且未发生渗透破坏。该渗流计算和安全评价方法可为今后类似工程大坝渗流安全评价提供借鉴。

小型水库土石坝安全评价主要技术问题探讨

我国的水库大坝多数已完成过一次安全鉴定或除险加固,运行状态和安全性状有所改变,近期进入了新一轮的安全评价周期。随着新的大坝安全评价导则及相关标准的实施,对大坝安全评价提出了一些新的要求。在新一轮的大坝安全评价工作中,不同的评价单位对一些常见技术问题作出了不同判断,导致安全评价结论大相径庭,也影响了后续的除险加固工作。本文对照新导则的基本技术要求,对这些常见的技术问题进行了梳理,剖析问题的本质,以利于提高大坝安全评价的准确性。