Effect of Seismic Permanent Deformation on Safety and Stability of Earth-Rock Dam Slope

In order to study the effect of seismic permanent deformation on the safety and stability of earth-rock dam, the permanent deformation is considered as the non-design permanent load, and the stress-strain hysteresis curve is also considered when the earth is under cyclic load. The research work can make the calculation results of plastic collapse more accurate by including the effect of the post-earthquake degree of plastic deformation on the stability of the earth-rock dam, and the dam safety factor decreases from 2.50 to 1.90 after the magnitude-8 earthquake. Moreover, the research work will also improve the design of the earth-rock dam under abnormal operating conditions.

Comparison between the Isotope Tracking Method and Resistivity Tomography of Earth Rock-Fill Dam Seepage Detection

This paper compares the different inversion results of three different earth rock-fill dam models with the actual leakage passages by performing isotope tracing tests and resistivity tomographic tests. The accuracy of the experimental results is evaluated, and the characteristics of these two methods are analyzed. As a result, some significant references are offered for earth rock-fill dam’s hidden defects detection. The experimental results show that the leakage and the direction of the seepage can be judged by isotope tracing tests, meanwhile, the degree of the leakage can be confirmed through the determination of the horizontal seepage velocity and the vertical seepage velocity, but it is difficult to properly determine the position of leakage passages and the range of leakage. Relatively speaking, the positions of the leakage passages can be accurately and directly displayed through resistivity tomographic tests. The experiment results show that the resistivity tomographic method is much better than isotope tracing method with regard to earth rock-fill dam’s hidden defects detection, and the resistivity tomographic method expresses much more convenience and much higher precision than isotope tracing method.

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.

Characteristics and factors that influenced damage to dams in the M_s 8.0 Wenchuan earthquake

Based on raw data from dams damaged in the Wenchuan earthquake, including many that were severely damaged, characteristics and factors that influenced the damage are discussed in this paper. Findings from this study include： severely damaged dams were densely distributed along the seismologic fault; small dams, especially small earth-rock dams, had the most serious damage that was caused by a variety of factors; the most serious damage was caused by seismic waves; damage was aggregated by aftershocks; and the extent of the damage patterns increased with the seismic intensity. Damage patterns varied in different intensity zones and cracking was the most common type of damage. Most of the dams had a good base with relatively high bearing capacity, and the walls of the earth-rock dams were mostly of clay soil. This type of base and body material mitigated some of the damage to dams. Reservoir maintenance and other factors also have a significant impact on the seismic safety of the dam. Finally, some recommendations to reduce seismic damage to dams are proposed.

Application of 3D Electrical Resistivity Tomography for Diagnosing Leakage in Earth Rock-Fill Dam

The leakage occurs during operation of the dam in Liuhuanggou reservoir. It’s a threat to the safety of the people’s lives and property in downstream. In order to eliminate the hidden danger of reservoir, ensure the safety of the dam, play better the function of flood control and water storage of the reservoir etc., we apply the 3D electrical resistivity tomography detecting technology and volume rendering image processing technology, make the measurement in field, process the data and combine the field survey to find out the leakage channels inside the dam. The results show that the 3D resistivity images appear the low resistivity zone corresponding with the leakage channels. There are two main leakage channels that come from different location inside the dam. It is feasible to diagnose the leakage in earth rock-fill dam by applying 3D electrical resistivity tomography.

Dynamic Risk Assessment Index System for Earth-Rock Dam during Construction

During the construction of earth-rock dam,mutual exclusive construction goals such as quality,safety,progress and cost all have influences on each other,with risk factors being everchanging as the construction progresses.Accurate identification of the risk factors,as well as clearing any possible effect that any risk factors might have on the construction project is the key and foundation to our cooperative control of the construction goals.According to the construction planning of earth-rock dam,the hall3 D structure was used to identify the potential changes of risk factors,and the possible means of any risk factors to interfere with the construction goals.The dynamic risk assessment index system is established by deploying the WBS-RBS(work breakdown structurerisk breakdown structure)method,aiming at the construction goals of earth-rock dam.The case study shows that the index system is very effective at risk management of earth-rock dam during construction,and relatively practicable.

RESEARCH ON SEEPAGE MONITORING MODEL OF EARTH-ROCK DAM

With the characteristics of seepage flow in earth-rock dams, a seepagemonitoring model was established based on the finite element method for 3-D seepage flow togetherwith observed data and was used to analyze and monitor the seepage of dams. In order to find out andmonitor the seepage status of the whole dam, the separation of seepage a-mount for dam body, damfoundation and side banks was made theoretically by using the model. Practical example shows thatthe accuracy of computed results is satisfactory and the separation results are more objective.

P2PSand和Finn本构模型在水库土石坝液化模拟中对比

为了研究地震作用下水库土石坝饱和砂土坝基可液化土层的影响规律,以某水库土石坝为背景,运用FLAC3D分析Practical Two-surface Plastic Sand(简称P2PSand)本构模型和Finn本构模型下的水库土石坝可液化粉砂层的液化分布规律、坝体变形特点以及坝坡的稳定性。计算结果表明:P2PSand模型下可液化粉砂层的液化程度、范围以及水库土石坝坝体位移均大于Finn模型,水平位移较显著;两种本构模型下水库土石坝坝体均出现两条明显的滑动面,稳定性降低。

冻结作用下土石坝护坡土石混合体水分迁移试验研究

土石坝护坡冻胀破坏主要由护坡砂砾料垫层、坝体填土自身冻胀和水分迁移共同作用引起。针对寒区土石坝护坡普遍存在的隆起、错位、坍塌等冻胀破坏问题,以寒区某土石坝护坡工程砂砾料垫层、坝体填土为研究对象,采用自研的土石混合体水分迁移冻结模型试验装置系统,开展了补水条件下单向冻结模型试验研究,研究了温度、含石量、水分迁移对土石坝护坡土石混合体冻胀特性的影响。研究结果表明:温度、含石量对土石混合体的冻胀特性影响显著;水分迁移受土石含量、温度和含水率影响,护坡砂砾料垫层和坝体填土含水率越大,冻结过程中水分迁移量越大,水分相变成冰的条件越充分;土、石分层对黏土温度变化影响较大,黏土和砾石分层可有效减小水分迁移量和冻胀量,对土石坝护坡防冻胀是有利的;土石混合体内部孔隙水相变成冰并在试样内部形成分凝冰是冻胀量增加的主要原因,土石混合体原位冻胀以及冻结过程中分凝冰的生长使冻胀量不断增加,且补水量越大,试样冻胀量就越大;不同温度、含石量下试样的冻胀量均随补水量的增加而基本呈线性增大,且含石量对冻胀量增加速率影响较小,温度对冻胀量增加速率影响较显著。研究成果可为寒区土石坝护坡设计和运行管理提供科学依据和技术支撑,补充了碾压式土石坝设计规范中的护坡设计。

沥青混凝土心墙堆石坝心墙拱效应研究

心墙拱效应是影响土石坝安全稳定运行的重要因素,心墙力学特性复杂且受众多因素的影响,复杂地形地质条件对心墙拱效应具有重要影响。首先对比了直心墙、斜心墙、下直上斜式心墙拱效应的差异,在此基础上选取岸坡坡度、河谷宽度、覆盖层厚度以表征坝体所处的地形地质条件。基于数值计算定量研究复杂地质条件对沥青混凝土心墙拱效应的影响规律。结果表明:心墙应力拱效应主要集中在心墙中部3/4坝高附近及靠近岸坡处;斜心墙应力拱效应相对较小,可以很好地改善心墙的整体受力状况;岸坡变陡,斜心墙整体的拱效应强度增加,应力传递的核心区域由心墙中部拓宽至心墙两岸坡;随着河谷宽度的增加,应力传递的重心逐渐由底部转移到心墙两岸及心墙中上部;斜心墙整体的应力拱效应并非随着河谷宽度的增加单调变化,当坝轴线长度与坝高比值增加到3~4时,河谷产生的河谷效应对斜心墙变形及拱效应的影响大幅下降;随着覆盖层厚度的增加,斜心墙底部的拱效应明显增强,底部的拱效应系数分布逐渐集中化、区域化,容易产生局部破坏。

土石坝护坡冻胀破坏水-热-力耦合数值模拟研究

针对寒区土石坝护坡普遍存在的冻胀破坏问题,选取寒区某土石坝工程为研究对象,结合土石坝工程特点,建立考虑水-热-力耦合作用的有限元计算模型。研究护坡在库水位和坝体填土水分迁移作用下冻胀破坏全过程,分析土石坝温度场、水分场和位移场的变化规律,并将位移场有限元计算结果与实测冻胀变形资料进行对比,验证有限元计算结果。研究结果表明:冻胀作用对坝坡影响深度约为2 m,坝坡浅层0~2 m范围的温度变化受外界气温影响较大,坝体内部温度相对坝坡浅层变幅小,且有一定的滞后性;负温使坝坡浅层孔隙水相变成冰,宏观上表现为未冻水体积分数的降低,坝坡浅层土石混合体孔隙水相变、坝体填土内水分向坝坡迁移和冻结峰面向坝体内部移动是护坡冻胀破坏的主要因素;大坝坝坡计算冻胀量为20~30 cm,最大值为36 cm,计算结果与实测冻胀变形资料吻合;护坡冻胀破坏主要由砂砾料垫层、坝体填土等土石混合体冻胀及冰推力共同作用引起。研究结果可为寒区土石坝护坡设计提供参考。

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.

堰塞湖土石坝漫顶溃坝扩散模型

依据推移质输沙率公式及河床变形方程,建立了堰塞湖土石坝溃坝冲刷过程的扩散模型,并给出了溃口纵剖面侵蚀下切与横断面展宽的解析解及其冲刷系数A计算公式。再联解水库调蓄方程和宽顶堰流量公式,用Excel计算表格得到了坝址溃口处流量与流速过程线,溃口底部高程及库水位降落过程线,溃口底部宽度与水面宽度变化过程线,以及最终纵、横剖面侵蚀形状。该模型理论严谨,计算简单,经模型试验、堰塞湖坝、土石坝溃坝实测资料验证符合良好,可应用于堆石坝、黏土坝、堰塞湖坝、尾矿坝、防洪堤等工程的溃坝抢险设计。

高土石坝变形监测研究进展

土石坝变形协调控制对保证其全生命期安全至关重要,准确可靠的变形监测是评估大坝变形性态、进行变形控制的基础。我国土石坝设计水平与建造技术已达到世界领先水平,其建设高度已迈入300 m级,安全监测技术也得到显著提升。本文总结了土石坝变形监测技术的发展与实践,介绍了分布式光纤传感、管道监测系统、GNSS/北斗、InSAR等新型内外观变形监测技术的工作原理、应用情况、技术优势和局限性,并简述了监测资料整编工作的相关进展。最近建成和在建的几座高土石坝已初步呈现了多技术协同、测点密集化等新态势,可全方位感知土石坝变形,为大坝安全评估提供了良好的数据基础。未来需进一步提升监测仪器可靠性与寿命,研发适用于超深厚覆盖层巨型土石坝的监测技术和仪器,研究海量多源异构监测数据治理理论与方法,全面提升复杂条件下的土石坝安全监测能力和数据治理水平。

近断层地震动作用下土石坝加速度分布研究

近断层地震动较远场地震动具有频率高、速度快、能量更加集中的特点,在短时间内会释放大量能量,对工程结构具有严重危害。规范提供的加速度分布系数不适用于高度超过150 m的大坝,随着技术不断进步,我国超过150 m的土石坝越来越多,规范已不能满足现有需求。基于中国台湾集集近断层地震动记录,建立随机脉冲型地震动模型,分别对高度为40 m、70 m、150 m和200 m的土石坝进行随机动力分析,研究坝体的动态分布系数。结果表明,近断层地震动的低频速度脉冲使坝体的加速度反应谱有较宽的敏感段,易覆盖坝体自振周期,显著增加坝体的加速度。该研究通过总结近断层区域土石坝的加速度分布规律,建议了近断层脉冲型地震动区域的土石坝坝体动态分布系数,为近断层高地震风险情况下土石坝的抗震理论和方法提供参考。

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。

基于随机动力分析的高土石坝极限抗震能力研究

地震动的随机性对大坝的动力响应影响较大,极限抗震能力作为大坝抗震安全性能的重要环节,在评估过程中也应该充分考虑荷载随机性的影响。基于大量高土石坝随机动力有限元计算,探究坝顶震陷率和坝坡累计滑移量两个重要坝体变形指标之间的关系,并建议了土石坝安全控制标准。利用概率密度演化法对高土石坝进行极限抗震能力分析。结果表明:震陷率随着累计滑移量的增大而增大,二者之间符合逻辑斯蒂增长模型;取10%的超越概率,以250m规则高面板堆石坝和高心墙堆石坝为例,极限抗震能力分别为0.7g~0.75g和0.8g~0.85g;从概率角度提出了评估大坝极限抗震能力的新方法。

基于本体和自然语言处理的土石坝险情知识图谱构建方法研究

土石坝在运维阶段可能受施工质量低、极端环境灾害等因素的影响,从而发生滑坡、裂缝、洪水漫顶等一系列险情。现阶段与土石坝险情相关的大量数据存储分散、结构多样,难以直接转化为经验和知识得到有效利用,快速指导险情处置。本研究针对土石坝险情领域提出了基于本体和自然语言处理(NLP)的知识图谱(KG)构建方法,分别采用自顶向下与自底向上法,构建图谱的模式层和数据层。模式层围绕险情类型、险情原因、险情措施三大概念,从土石坝结构、过程、环境、材料4方面建立领域本体库,搭建KG的概念结构。数据层通过数据预处理、知识抽取、语义对齐等操作,运用NLP对文本进行处理并根据语料的特征建立相应的提取规则,获得数据层的具体知识内容。最后以三元组形式存储不同类型的实例和相互关系,运用Neo4j图数据库进行土石坝险情领域KG的可视化表达及查询应用,使领域内分散数据向集成知识转化,为土石坝安全管理和险情处置提供技术和理论支持。

低围压与不同温度作用下土石坝护坡土石混合体力学特性

针对寒区土石坝护坡存在的隆起、错位、坍塌等冻胀破坏问题,以寒区某土石坝护坡工程砂砾料垫层、坝体填土土石混合体为研究对象,开展了低围压下不同温度和含石量的土石坝护坡土石混合体三轴试验,研究了不同围压、温度、含石量对土石混合体力学特性的影响。结果表明:在较低围压作用下,含石量较低试样的应力-应变关系曲线为应变软化型,随着围压增大,试样的应力-应变关系曲线变为应变硬化型;在常温条件下,当围压较低时,不同含石量的试样呈现先剪缩后剪胀的现象,当围压较高时,试样则一直表现为剪缩,且围压越大,剪缩量越大;在不同冻结温度下,土石混合体的体积应变呈现先剪缩后剪胀的变化规律,且试验温度越低,剪胀变形越明显;随着含石量的增加,砾石之间的嵌合作用增强,土石混合体逐渐成为砾石骨架结构,土石混合体的内摩擦角增大而黏聚力减小;温度的降低使得土石混合体试样内部的水逐渐相变成冰,在结冰胶结作用下,土石混合体的内摩擦角和黏聚力都有所增加。

基于时序InSAR的老挝桑片-桑南内水库大坝溃坝回溯研究

InSAR是一种用于水库大坝表面位移监测的新技术,具有周期性、低延迟的特点,且能回溯历史数据。利用老挝桑片-桑南内水库大坝溃坝前期及溃坝期间的卫星影像,收集溃坝前后的大坝表面位移监测数据和降雨数据,对大坝自身和管理方面的溃坝原因进行了分析,结果表明大坝溃坝前已发生较明显的异常变形趋势。本研究将InSAR技术引入大坝风险管理中,能有效减少溃坝事故的发生。