Stress-strain analysis of Aikou rockfill dam with asphalt-concrete core

Aikou rockfill dam with asphalt-concrete core is situated in a karst area in Chongqing City, China. In order to study the operative conditions of the rockfill dam, especially those of the asphalt-concrete core, the Duncan model is adopted to compute the stress and strain of both the rockfill dam and the asphalt-concrete core after karst grouting and other treatments. The results indicate that the complicated stress and deformation of both the dam body and the core are within reasonable ranges. It is shown that structure design and foundation treatment of the dam are feasible and can be used as a reference for other similar projects.

STUDY ON COUPLING MODEL OF (SEEPAGE-FIELD) AND STRESS-FIELD FOR ROLLED CONTROL CONCRETE DAM

Based on the construction interfaces in rolled control concrete dam(RCCD), the methods were proposed to calculate the influence thickness of construction interfaces and the corresponding physical mechanics parameters. The principle on establishing the coupling model of seepage_field and stress_field for RCCD was presented. A 3_D Finite Element Method(FEM) program was developed. Study shows that such parameters as the thickness of construction interfaces,the elastic ratio and the (Poisson's) ratio obtained by tests and theoretical analysis are more reasonable, the coupling model of seepage_field and stress_field for RCCD may indicate the coupling effect between the two fields scientifically, and the developed 3_D FEM program can reflect the effect of the construction interfaces more adequately. According to the study, many scientific opinions are given both to analyze the influence of the construction interfaces to the (dam's) characteristic, and to reveal the interaction between the stress_field and the seepage_field.

Numerical stress-deformation analysis of cut-off wall in clay-core rockfill dam on thick overburden

The cut-off wall in a clay-core rockfill dam built on a thick overburden layer is subjected to a large compressive pressure under the action of the loads such as the dead weight of both the dam and the overburden layer, the frictional force induced by the differential settlement between the cut-off wall and surrounding soils, and the water pressure. Thus, reduction of the stress of the cut-off wall has become one of the main problems for consideration in engineering design. In this paper, numerical analysis of a core rockfill dam built on a thick overburden layer was conducted and some factors influencing the stress-strain behaviors of the cut-off wall were investigated. The factors include the improvement of the overburden layer, the modeling approach for interfacial contact between the cut-off wall and surrounding soils, the modulus of the cut-off wall concrete, and the connected pattern between the cut-off wall and the clay core. The result shows that improving the overburden layer,selecting plastic concrete with a low modulus and high strength, and optimizing the connection between the cut-off wall and the clay core of the dam are effective measures of reducing the deformations and compressive stresses of the cut-off wall. In addition, both the Goodman element and the mud-layer element are suitable for simulating the interfacial contact between the cut-off wall and surrounding soils.

Seepage and stress analysis of anti-seepage structures constructed with different concrete materials in an RCC gravity dam

This study used the finite element method （FEM） to analyze the stress field and seepage field of a roller-compacted concrete （RCC） dam, with an upstream impervious layer constructed with different types of concrete materials, including three-graded RCC, two-graded RCC, conven- tional vibrated concrete （CVC）, and grout-enriched vibrated RCC （GEVR）, corresponding to the design schemes S 1 through $4. It also evaluated the anti-seepage performance of the imperious layer in the four design schemes under the normal water level and flood-check level. Stress field analysis of a retaining section and discharge section shows that the maximum tensile stress occurs near the dam heel, the maximum compressive stress occurs near the dam toe, and the stress distributions in the four schemes can satisfy the stress control criteria. Seepage field analysis shows that the uplift pressure heads in schemes S3 and S4 descend rapidly in the anti-seepage region, and that the calculated results of daily seepage flow under the steady seepage condition in these two schemes are about 30%-50% lower than those in the other two schemes, demonstrating that CVC and GEVR show better anti-seepage performance. The results provide essential parameters such as the uplift pressure head and seelga^e flow for physical model tests and anti-seepage structure selection in RCC dams.

General displacement arch-cantilever element method for stress analysis of arch dam

Based on the general displacement method and the basic hypothesis of the trial load method, a new advanced trial load method, the general displacement arch-cantilever element method, was proposed to derive the transformation relation of displacements and loads between the surface nodes and middle plane nodes. This method considers the nodes on upstream and downstream surfaces of the arch dam to be exit nodes （master nodes）, and the middle plane nodes to be slave nodes. According to the derived displacement and load transformation matrices, the equilibrium equation treating the displacement of middle plane nodes as a basic unknown variable is transformed into one that treats the displacement of upstream and downstream nodes as a basic unknown variable. Because the surface nodes have only three degrees of freedom （DOF）, this method can be directly coupled with the finite element method （FEM）, which is used for foundation simulation to analyze the stress of the arch dam with consideration of dam-foundation interaction. Moreover, using the FEM, the nodal load of the arch dam can be easily obtained. Case studies of a typical cylindrical arch dam and the Wudongde arch dam demonstrate the robustness and feasibility of the proposed method.

Study on main contents of design of rock fill dam with face slab

With the development of economy, the adjustment of industrial structure, the improvement of people＇s living standard and the expansion of urbanization, the structure of the city has changed a lot. The proportion of industrial use of electricity decreased year by year, the proportion of household electricity, commercial electricity and public utilities increased year by year, the peak and valley change increased year by year. Therefore, the construction of hydropower project, to improve the current situation of the system of regulating the power grid, has a positive role in promoting. Reinforced rock fill dam with face slab in foreign countries has been built and at the dam more than 50m high dam more than 70 seats, of which more than 100m high dam 18. At present, Brazil estuary aliya rock fill dam is the highest dam in this kind of dam in the world, built in 1980, has been running well. Our reinforced rock fill dam with face slab design and construction technology in the introduction of digestion and absorption of foreign advanced experience in the foundation, the systemic research on a considerable scale. The design level and construction technology of the rock fill dam with face slab in our country have reached the international advanced level by the complete technology of the construction of the 100m level rock fill dam with face slab. This paper mainly from the rock fill dam with face slab, dam type selection and layout of water conservancy project comparison; dam profile design; detail dam; dam high determined; stability analysis; strength calculation; overflow capacity check aspects were studied.

水体DAMS暴露对异育银鲫肝胰脏和鳃的氧化胁迫及组织学影响

探究了阴离子表面活性剂十二烷基苯磺酸异丙胺盐(DAMS)对异育银鲫(Carassiusauratusgibelio)肝胰脏和鳃组织的氧化胁迫和组织学的影响.异育银鲫在水体不同浓度的DAMS中暴露28d后,测定肝胰脏和鳃组织中丙二醛(MDA)含量、超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-PX)活性以及观察肝胰脏和鳃组织的组织学切片.结果表明,DAMS对异育银鲫的96h半致死浓度LC50为19.83mg·L-1;在亚急性暴露实验中,随着毒物浓度升高,异育银鲫肝胰脏和鳃组织的GSH-PX和SOD活性均表现出显著的抑制(P<0.05),肝胰脏中MDA含量随暴露浓度的升高先上升后下降;高浓度暴露组鳃组织中MDA含量与对照组无显著差异,高浓度暴露组实验鱼的肝细胞出现明显的空泡化,鳃组织出现鳃上皮脱落等不同程度的损伤.结果暗示水体中的DAMS暴露对异育银鲫具有一定的氧化胁迫毒性.

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.

Nonlinear simulation of arch dam cracking with mixed finite element method

This paper proposes a new, simple and efficient method for nonlinear simulation of arch dam cracking from the construction period to the operation period, which takes into account the arch dam construction process and temperature loads. In the calculation mesh, the contact surface of pair nodes is located at places on the arch dam where cracking is possible. A new effective iterative method, the mixed finite element method for friction-contact problems, is improved and used for nonlinear simulation of the cracking process. The forces acting on the structure are divided into two parts： external forces and contact forces. The displacement of the structure is chosen as the basic variable and the nodal contact force in the possible contact region of the local coordinate system is chosen as the iterative variable, so that the nonlinear iterative process is only limited within the possible contact surface and is much more economical. This method was used to simulate the cracking process of the Shuanghe Arch Dam in Southwest China. In order to prove the validity and accuracy of this method and to study the effect of thermal stress on arch dam cracking, three schemes were designed for calculation. Numerical results agree with actual measured data, proving that it is feasible to use this method to simulate the entire process of nonlinear arch dam cracking.

基于PCA-SSA-XGBoost算法的拱坝应力预测模型研究

由于大坝应力受水位、温度等众多因素共同作用,各影响因子间的相互关联会引起多重共线性问题,容易导致以此为输入的预测模型出现伪回归现象。此外,现有基于机器学习算法的应力预测模型由于训练特征过多、过度训练易产生过拟合现象,其预测精度还有待提高。针对上述问题,提出了基于主成分分析法(PCA)和麻雀搜索算法(SSA)改进的极限梯度提升算法(PCA-SSA-XGBoost)构建拱坝应力预测模型。该模型首先采用主成分分析法对参数进行降维,降低影响因子的多重共线性影响;进而通过SSA算法优化XGBoost的超参数,以避免传统算法过拟合,进一步提高模型预测性能。将该模型应用于我国西南某混凝土拱坝工程,对应力及应力相关监测数据进行处理、分析和预测,并与多元线性回归模型(MVLR)、神经网络模型(RBFNN)、极限梯度提升回归预测模型(XGBR)的预测结果进行对比分析。结果表明,基于PCA-SSA-XGBoost算法的应力预测模型可克服输入变量的多重共线性和过拟合问题,在预测精度方面具有优越性。

250 m级特高面板堆石坝混凝土面板顺坡向应力控制措施研究

面板应力变形控制是建设250 m级特高混凝土面板堆石坝的关键难题.大量工程实测案例和研究计算表明,特高面板坝压应力常处于较高水平,对于坝轴向应力来说,采用柔性缝降低压应力措施已被工程界普遍接受,然而,目前对于如何降低面板顺坡向压应力尚缺少有效的解决方法.本文以拟建的240 m级GS面板坝为研究对象,从特殊增模区布置、面板施工顺序、面板低高程柔性横缝、高压力区高强度混凝土材料等4个方面提出改善面板顺坡向应力的工程措施.文中通过三维有限元精细模拟方法分析了提出的顺坡向应力改善措施的效果,文中提出的措施可为250 m面板堆石坝面板应力控制提供借鉴.

Comparison of Design and Analysis of Concrete Gravity Dam

Gravity dams are solid concrete structures that maintain their stability against design loads from the geometric shape, mass and strength of the concrete. The purposes of dam construction may include navigation, flood damage reduction, hydroelectric power generation, fish and wildlife enhancement, water quality, water supply, and recreation. The design and evaluation of concrete gravity dam for earthquake loading must be based on appropriate criteria that reflect both the desired level of safety and the choice of the design and evaluation procedures. In Bangladesh, the entire country is divided into 3 seismic zones, depending upon the severity of the earthquake intensity. Thus, the main aim of this study is to design high concrete gravity dams based on the U.S.B.R. recommendations in seismic zone II of Bangladesh, for varying horizontal earthquake intensities from 0.10 g - 0.30 g with 0.05 g increment to take into account the uncertainty and severity of earthquake intensities and constant other design loads, and to analyze its stability and stress conditions using analytical 2D gravity method and finite element method. The results of the horizontal earthquake intensity perturbation suggest that the stabilizing moments are found to decrease significantly with the increment of horizontal earthquake intensity while dealing with the U.S.B.R. recommended initial dam section, indicating endanger to the dam stability, thus larger dam section is provided to increase the stabilizing moments and to make it safe against failure. The vertical, principal and shear stresses obtained using ANSYS 5.4 analyses are compared with those obtained using 2D gravity method and found less compares to 2D gravity method, except the principal stresses at the toe of the gravity dam for 0.10 g - 0.15 g. Although, it seems apparently that smaller dam section may be sufficient for stress analyses using ANSYS 5.4, it would not be possible to achieve the required factors of safety with smaller dam section. It is observed during stability analyses that the factor of safety against sliding is satisfied at last than other factors of safety, resulting huge dam section to make it safe against sliding. Thus, it can be concluded that it would not be feasible to construct a concrete gravity dam for horizontal earthquake intensity greater than 0.30 g without changing other loads and or dimension of the dam and keeping provision for drainage gallery to reduce the uplift pressure significantly.

堆石料本构模型对混凝土面板坝应力变形计算结果的影响研究

堆石料本构模型选择是影响混凝土面板坝应力变形计算结果的主要因素。以某典型面板坝为例,采用邓肯E-B非线性弹性模型和“南水”双屈服面弹塑性模型,对坝体填筑过程和蓄水过程进行了三维有限元模拟;研究了两种模型计算的坝体和面板的位移和应力分布差异;分析了两种模型计算结果呈现差异的原因。两种模型计算结果最显著的差异体现在两个方面:(1)“南水”模型计算的坝体沉降、面板挠度等位移指标小于E-B模型,其原因是“南水”模型计算的坝体小主应力和变形模量更高。(2)E-B模型计算结果显示蓄水后面板底部顺坡向受拉;而“南水”模型计算的面板顺坡向应力为全断面受压。前者是由E-B模型的各向同性弹性本质决定的,垫层料因水压力作用顺坡向膨胀,产生沿坡面向上的位移;后者是其F1屈服面持续扩张产生塑性体积收缩导致的,塑性体缩抵消了顺坡向弹性膨胀,使垫层料产生沿坡面向下的位移。

混凝土面板与堆石料接触面模型及其应用

混凝土面板是面板坝防渗安全的生命线,其应力变形特性主要取决于坝体堆石料的应力变形特性及面板与堆石料之间的接触特性。在面板坝的应力变形计算中,通常采用接触面模型模拟面板与堆石料之间的荷载传递机制,因此接触面模型是否合理,直接影响到面板应力变形计算结果的可靠性。分析了传统双曲线接触面模型存在的不足,提出了一个考虑双向剪切耦合效应,且符合强度准则和标架无差异原则的接触面本构模型,该模型参数少,数值实现方便,可以定性地模拟出实际面板坝工程中出现的混凝土挤压破坏区域。

基于温度应力仿真的仙洞沟堆石混凝土坝分缝技术研究

堆石混凝土重力坝是否分横缝及分缝间距对大坝温度应力影响很大,在相同环境下,坝体不分缝或横缝间距越大,温度应力越大,大坝开裂风险也越高;但不分缝或长距离分缝,可有效简化施工工序,实现快速连续施工,能充分体现该坝型优势。该研究针对仙洞沟水库工程实际,对堆石混凝土大坝整体不分缝和超出规范规定的长距离坝段分缝方案进行研究,基于不同的温控措施进行温度应力三维仿真分析,在最终确定大坝的分缝和温控方案的同时,进行有益探索,推动了堆石混凝土筑坝技术的发展。

渗流—应力耦合下隧道爆破开挖对邻近水坝影响因素分析

为研究隧道爆破施工作用下邻近水库大坝的安全性,以浙江义东高速公路防军隧道出口段麻车坑水库为研究对象,通过理论分析阐述了大坝的振动破坏过程,利用有限元软件MIDAS GTS NX数值模拟的手段,探讨了不同爆破炸药量、爆心距、坝前水位变化对水库大坝稳定性的影响,揭示了水库大坝应力与振速的变化规律,并进一步引入Morris筛选法对各因素的影响程度进行评价分析。研究结果表明,影响水库大坝稳定性控制变量因素的主次关系为炸药量>爆心距>坝前水位;水库大坝的应力峰值与振速峰值随着隧道炸药量的增大、坝前水位的增高、爆心距的减小而增大;隧道爆破施工时,可以采取提前排放库水、控制炸药量及爆心距等方式使水库大坝受到的损伤降到最低,研究结论可为邻近隧道爆破施工水库安全防护提供参考与借鉴。

叶巴滩堆石混凝土二道坝温度应力仿真分析及温控措施研究

对位于高海拔地区的叶巴滩堆石混凝土二道坝工程开展全坝段温度应力仿真分析,重点研究大坝横缝分缝措施和混凝土表面保温措施对坝体温度应力的影响。结果表明:结构分缝措施可以降低坝体内部拉应力,设置1条横缝即可有效控制坝体内部高拉应力区范围,并使应力极值降低约0.8 MPa;混凝土表面保温措施可在秋冬季节显著降低大坝表层混凝土温降幅度,减小表层温度应力水平,使应力极值降低约0.6 MPa;叶巴滩二道坝设置1条横缝并采取表面保温可满足施工期温控要求。

土石坝加高工程老坝防渗墙施工时机优选

针对老旧水库大坝加高工程中混凝土防渗墙的修建时机对其自身应力变形影响很大,可能对坝体防渗系统造成安全隐患的问题,以某土石坝加高工程为例,采用三维有限元法对大坝加高过程进行模拟计算,分析比较了不同施工方案下防渗墙的应力变形特性,以优选防渗墙施工时机。模拟计算结果表明:在加高坝填筑至215 m或此之前修建老坝防渗墙时墙体应力变形较小,此时竣工期与蓄水期防渗墙顺河向最大位移分别为-1.56 cm与4.91 cm,大主应力极值分别为1.01 MPa与1.67 MPa,小主应力极值分别为-0.41 MPa与-0.66 MPa,防渗墙与连接板接缝的切向错动和相对沉降变形极值分别为4.84 mm与8.11 mm,能够满足安全运行要求。相比加高坝填筑后期施工防渗墙,在加高坝填筑开始前或填筑至与老坝同高之前完成防渗墙的施工,可改善防渗墙的应力变形状态并降低防渗墙与连接板接缝的切向错动和相对沉降。

远场水下爆炸冲击作用下重力坝动力稳定性的简化时程分析方法

高坝大库的抗爆与防护是国防安全的重要研究课题。该文针对远场水下爆炸冲击作用下混凝土重力坝的稳定安全评价问题,研究了远场水下爆炸冲击波的传播及其与坝体的相互作用过程;基于波动理论和平面波假设,建立了重力坝爆炸动应力场的简化理论计算模型,最终建议了一种远场水下爆炸冲击波作用下重力坝动力稳定性的简化时程分析方法;同时结合工程实际,采用该方法对某混凝土重力坝的动力稳定性进行了分析。结果表明:在远场爆炸冲击荷载作用下,重力坝的稳定安全系数呈现出先增后减再增并最终保持恒定的变化规律;下游坝面反射形成的拉伸波与剪切波的共同作用是导致建基面稳定安全系数降低的主要原因。

过渡料特性对沥青混凝土心墙开裂的影响

沥青混凝土心墙的应力水平变化不仅受自身材料特性影响,也受相邻过渡料特性的制约,改变过渡料特性会对心墙水力劈裂产生较大影响。为探明过渡料特性变化与心墙开裂之间的关系,采用邓肯张E-B模型对庙堂心墙堆石坝进行有限元计算,提出了抗裂安全系数Kn来表征心墙发生水力劈裂的危险程度,并在此基础上采用正交实验的方法比较了过渡料E-B模型各个参数与心墙开裂的相关性,得出结论:过渡料刚度越大,心墙发生水力劈裂可能性越大;在过渡料选择上,应当优先考虑高敏感性因素破坏比(R_(f))、卸荷再填筑时的弹性模量指数(n)、土体内摩擦角(φ_(0))、初始弹性模量(K),在满足沥青混凝土心墙坝设计和施工规范的前提下,选取R_(f)较大,K、φ_(0)较小的过渡料,能够有效提升沥青混凝土心墙坝抗裂性能。