Kafrein Earth dam probabilistic seismic hazard assessment

The primary seismic source contributing to the hazard at the Kafrein dam site is the active Jordan Valley fault, which extends from the Dead Sea to the Sea of Galilee, with an expected maximum earthquake magnitude of 7.5 and greater. This paper presents a seismic hazard assessment of the dam under earthquake events. __________ Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 6, pp. 18–21, November–December, 2006.     

Monitoring and analysis of settlement and stability of an embankment dam constructed in stages on soft ground

 This study is concerned with Karameh dam, an earth-fill dam constructed on soft ground. It is located on Wadi Mallaha adjacent to the Jordan River on the eastern side of the Jordan Rift Valley. The project involved 11.2 million m³ of zoned earth fill, about 6 million m³ of excavation, a spillway and draw-off structures. The total height of the dam is 45 m and the total capacity of the reservoir 55 million m³. The construction of the dam on soft ground generated positive excess pore-water pressures within the underlying foundation soils. The dam was constructed in stages to achieve the required level of safety and to monitor/control the settlement development. The study reported here involved analysis, assessment and interpretation of the geological, geotechnical and monitoring data obtained during the staged construction of the Karameh embankment dam. Available soil mechanics models related to 1-D, 2-D and 3-D consolidation theory, undrained settlement, stress history and normalised soil engineering properties were used in the study. The overall stability of the Karameh dam embankment and foundations was evaluated using effective stress analysis (ESA) and total stress analysis (TSA) methods. Received: 5 July 1999 · Accepted: 15 April 2000     

Geological and geotechnical characteristics of Karameh dam site, north of the Dead Sea, Jordan

This paper describes a feasibility stage geotechnical evaluation carried out at the Karameh dam site. The 45 m high, 2,150 m long dam will be built across the Wadi Mallaha on Quaternary lacustrine deposits and store fresh water from the King Abdullah Canal. A confined highly saline aquifer was identified at a depth of 25 m, the saline groundwater migrating naturally through the Lisan Formation. Stability analysis of the foundation indicates that the slopes are just stable under dry conditions and may become unstable under wet conditions. The most important problem is the presence of the active main Jordan Valley Fault crossing both the dam body and reservoir. Electronic Publication     

Remedial measures to control seepage problems in the Kafrein dam, Jordan

The Kafrein dam, 480 m long and 30 m high, is located on the Wadi Kafrein, a few kilometres from the active Jordan Valley fault. The Jordan Valley Authority proposed raising the crest of the existing dam by approximately 7 m and extending the length of the embankment to 554 m, in order to increase its storage capacity by 6 million m³ to a total of 8.5 million m³. The paper discusses the likelihood that existing seepage problems will be exacerbated when the dam is raised and proposes some remedial actions to increase the safety of the dam and minimise both the amount of seepage and any adverse effects. Electronic Publication     

基于改进CM模型的土石坝三维弹塑性地震反应分析

基于交变移动性（CM）模型,引入饱和度作为状态变量,给出了改进的土体塑性势面方程、屈服方程和协调方程,推导了新的硬化参量计算公式,发展了可连续描述非饱和与饱和土体静动力学特性的弹塑性本构模型。通过转换应力法,将模型从试验应力状态拓展到一般应力状态,使得本构模型可用于复杂三维河谷场地上修建的土石坝的弹塑性地震反应分析。数值模拟了汶川地震中典型震损土石坝的震害过程,模拟结果与实际震害吻合较好。对比研究了输入地震动强度对土石坝弹塑性地震反应分析结果的影响,结果表明土体的弹塑性特性对坝-基动力相互作用有着较大影响。     

Coquitlam大坝抗震能力提高设计(英文)

Coquitlam 大坝建于 1913 年,坝高 30 m,为吹填土石坝。大坝位于加拿大 BC 省高地震危险带。风险人口数以万计。根据现行标准,大坝的抗震能力不符合要求,坝体冲填土和某些部位地基土松散,容易液化。在中度至重度的地震情况下,大坝将会遭受严重的损坏,并有可能溃决。提高大坝的抗震能力很有必要。选择最高设计地震为里氏7.5 级地震,地震地面水平峰值加速度 0.66g。在设计中,还需要对以下一些提高抗震能力的设计方案进行评估,包括结构修复、大坝重建、限制水库运行及退役。在综合考虑技术、社会、环境和经济因素的基础上,选择了兴建一座新的下游堤坝以提高其抗震能力,减少 Coquitlam 大坝的地震风险。新建坝包括一座土质心墙堆石堤坝和一个位于左坝肩的混凝土过渡带。新建堤坝大部分是建在具有承载力的淤泥土上,而混凝土过渡带则完全建在基岩上。由于现场和施工条件的限制,座落在现有大坝下游坝壳部分的新建堤坝上游坡的下部一小部分为沿原河道的液化砂砾石冲积层。先进的地震稳定性和变形分析结果表明,由于有足够的超高、厚厚的反滤体以及过渡带,大坝所产生的变形是可以接受的。为了控制基础渗流和出逸坡降,设计采用了塑性混凝土防渗墙、帷幕灌浆以及在下游增设一套减压井相结合的方案。为了监测新建坝的性态,在施工期和运行期的仪器监测设计中采用了基于破坏模式的方法。主要介绍了 Coquitlam新建堤坝的设计,包括大坝安全监测系统的设计。     

高雄捷运大寮主机厂基地土壤液化潜能评估分析

以GPS/GIS/RS科技整合应用 ,对大寮主机厂基地区域环境与其工址地层特性进行汇整分析。由于高雄捷运系统大寮主机厂为捷运总部及行控中心所在 ,故针对大寮主机厂厂址基础地层的潜在灾害特性进行调查分析研究 ,很有必要。本研究采用NJRA法结合Iwasaki深度加权法 ,并特别考虑细粒料含量、地表最大加速度与填土静态加载等不同参数值的影响 ,对该厂址基础地层液化潜能进行评估。其结果显示邻近孔号EB -19&EB -2 7的区域具有较高液化潜能 ,只有当PGA =0 .18g且填土高度达 3m时 ,厂址地层液化潜能可降低至低度液化潜能范围 ;若以PGA =0 .3 3g作分析时 ,厂址各分区均属极高度液化潜能范围。本研究最后汇整大寮主机厂区环境特性与其基础地层灾害分析结果 ,建立该区域地层潜在灾害数据库系统 ,以利于判定厂区基础地层潜在土壤液化区的灾害空间分布趋势与掌握其特性变异 ,并为相关单位提供大寮主机厂基础地层土壤液化防治决策参考。     

Probabilistic assessment of earthquake hazard in Sinai in relation to the seismicity in the eastern Mediterranean region

Sinai is surrounded by the most active seismic trends in Egypt and earthquake risk reduction has become an important ongoing socio-economic concern. Twenty-five earthquake source zones were used to define the seismicity of the eastern Mediterranean region. Peak ground acceleration (PGA) values with a 90% probability of not being exceeded in 50 and 100 years were determined for the Sinai and Dead Sea regions. These indicated the highest relative levels of ground motion are expected in regions neighbouring the Gulf of Aqaba, the Dead Sea and the southern part of the Gulf of Suez. Other regions were characterized as having a relatively low to intermediate level of PGA values. The PGA values obtained will be useful for civil engineers, regulators and planners, in order to mitigate the effects of earthquakes and to plan earthquake resistant designs.     

Seismic site characterization for Moulvibazar town,Bangladesh

In recent years, decision-making and site-planning strategies for earthquake mitigation have shifted away from a crisis management approach, to a greater emphasis on risk reduction. The earthquake hazard of a particular area can be assessed using geophysical and geotechnical site investigations. In the present study, seismic site characterization was carried out to evaluate earthquake risk for the town of Moulvibazar, Bangladesh, by integrating geophysical and geotechnical approaches. The study revealed that the average shear wave velocity to a depth of 30 m (AVS30) varied from 150 to 235 m/s, and US National Earthquake Hazards Reduction Program (NEHRP) soil site classes D and E were predominant, with soil amplification factors (SAF) of 1.3 and 1.45 for site classes D and E, respectively. In addition, peak ground acceleration (PGA) at the ground surface ranged from 0.325 to 0.3625 g, foundation layer depths for the deep foundation varied from 15 to 29 m, and the predominant periods ranged from 0.35 to 0.72 s. These soil parameters can be used to prepare an earthquake risk-sensitive land use plan for future urban development and to design earthquake-resistant structures.     

Liquefaction assessments by field-based methodologies: foundation soils at a dam site in Northeast Turkey

Recent examples show that strong earthquakes can cause damage to dams, notably tailings or hydraulic fill dams or relatively small earth fill embankments. Liquefaction is known to be one of the most dangerous consequences of the dynamic loading of an embankment dam and hence must be considered during the dam site selection and construction stages. This paper presents the liquefaction analyses undertaken for the Demirözü dam site in Northeast Turkey. The liquefaction assessments are mainly based on field-performance data using SPT- and CPT-based methods in conjunction with the results of the available cyclic triaxial tests. The presence of a very shallow groundwater table, loose sandy layers and the seismic features of the region result in a high susceptibility to liquefaction. The results obtained from the SPT- and CPT-based criteria for evaluating the liquefaction potential are generally consistent and show that the thickness of the liquefiable layers increases in the area between the left bank and the central part of the proposed dam. Further studies are required to evaluate the suitability and efficiency of measures which could be taken to avoid liquefaction-induced problems at the dam site.     

Seismic stability of embankments subjected to pre-deformation due to foundation consolidation

It has been reported that the major cause of earthquake damage to embankments on level ground surfaces is liquefaction of foundation soil. A few case histories, however, suggest that river levees resting on non-liquefiable foundation soil have been severely damaged if the foundation soil is highly compressible, such as thick soft clay and peat deposits. A large number of such river levees were severely damaged by the 2011 off the Pacific coast of Tohoku earthquake. A detailed inspection of the dissected damaged levees revealed that the base of the levees subsided in a bowl shape due to foundation consolidation. The liquefaction of a saturated zone, formed at the embankment base, is considered the prime cause of the damage. The deformation of the levees, due to the foundation consolidation which may have resulted in a reduction in stress and the degradation of soil density, is surmised to have contributed as an underlying mechanism. In this study, a series of centrifuge tests is conducted to experimentally verify the effects of the thickness of the saturated zone in embankments and of the foundation consolidation on the seismic damage to embankments. It is found that the thickness of the saturated zone in embankments and the drainage boundary conditions of the zone have a significant effect on the deformation of the embankments during shaking. For an embankment on a soft clay deposit, horizontal tensile strain as high as 6% was observed at the zone above the embankment base and horizontal stress was approximately half that of the embankment on stiff foundation soil. Crest settlement and the deformation of the embankment during shaking were larger for the embankment subjected to deformation due to foundation consolidation.     

沉降监测在海堤修复工程中的技术应用

通过死海南端约旦18号海堤的沉降监测实例,论述了沉降监测在国外大型工程项目中的技术使用,并对该海堤的沉降监测方法进行了总结,最后得出该方法对动态监测大坝安全起到了十分重要的作用。     

爆炸液化场地上堤坝变形的模型试验研究

饱和砂土地基在地震、爆炸等振动荷载作用下易发生液化,从而使堤坝等上部构筑物发生破坏。开展了爆炸液化场地上堤坝变形的大型模型试验,考虑了筑坝材料以及堤坝地基加固措施对堤坝变形和坝身裂缝的影响。试验表明:堤坝沉降主要发生在场地液化后的1~2 h内,该段时间内产生的沉降占7 d时沉降量的84%~87%;掺加了碎石的堤坝比未加碎石的堤坝7 d时沉降量大24%;地基内采用土工格栅+土工布的加固措施能够有效减少堤坝在液化场地上的沉降,比未加固的堤坝沉降减少了10%。堤坝的裂缝主要出现在细骨料筑成的坝段和不同筑坝材料的交界处,沿坝身开展。总结了国内外规范中对于液化地基沉降的计算及预测方法,根据液化地基上浅基础建筑物沉降图表对试验中的堤坝沉降进行了推算,发现实测沉降与推算沉降比较接近。     

基于随机有限断层法的坝址地震动参数#br# 综合评价方法

对于受多条发震构造影响的大坝场址,合理估计坝址地震动输入是实现近场地震作用下不溃坝目标的前提条件。文章主要目标是对地震地质环境复杂的场址建立适合于工程应用的地震动参数评价方法。首先对随机有限断层法模拟近场大震的适用性进行分析,结果表明该方法不仅可以描述断层破裂源,考虑地震波路径、场地衰减等因素,而且计算效率高,能够解决地震动模拟中复杂震源设置与计算效率的问题,可用于大坝场址地震动参数估计;然后基于对随机有限断层法参数的不确定性分析,建立一套能够考虑多个发震构造对坝址影响的地震动参数综合评价体系,包括设置震源、路径及场地条件参数的取值范围及水平、设计多方案(多权重)地震动模拟方案、各参数取值的权重系数计算原则与方法;最后获得能够表征不同地震危险性的参数估计方法。该文建立的方法能够考虑坝址发震构造的复杂性,给出多层次、多风险水平的评价结果,为近场大震作用下大坝抗震安全评价提供合理的地震动参数。     

Liquefaction evaluation of dam foundation soils considering overlying structure

The liquefaction analysis procedure conducted at a dam foundation associated with a layer of lique fi able sand is presented.In this case,the effects of the overlying dam and an embedded diaphragm wall on liquefaction potential of foundation soils are considered.The analysis follows the stress-based approach which compares the earthquake-induced cyclic stresses with the cyclic resistance of the soil,and the cyclic resistance of the sand under complex stress condition is the key issue.Comprehensive laboratory monotonic and cyclic triaxial tests are conducted to evaluate the static characteristics,dynamic characteristics and the cyclic resistance against liquefaction of the foundation soils.The distribution of the factor of safety considering liquefaction is given.It is found that the zones beneath the dam edges and near the upstream of the diaphragm wall are more susceptible to liquefaction than in free fi eld,whereas the zone beneath the center of the dam is less susceptible to liquefaction than in free fi eld.According to the results,the strategies of ground improvement are proposed to mitigate the liquefaction hazards.     

花凉亭水库砂壳坝的抗震性能分析与加固研究

经过对花凉亭水库黏土心墙砂壳坝进行地质勘察取样试验和液化分析,由于其上游坝坡砂土密实度不够,在7度地震时,水下部分可能发生液化并产生滑坡,需要进行抗震加固处理。我国目前已进行过抗震加固的土石坝不多,工程经验较少,还没有成熟的加固设计方法和技术规范。本工程应用砂土动强度试验成果,采用动力有限元分析对大坝抗震加固方案进行技术论证,并提出了帮坡压重的抗震加固方案,即在上游坝坡的水下部分抛块石帮坡压重和水上部分填筑石渣料帮坡压重,有效解决了水库蓄水条件下的大坝上游坝坡的抗震加固问题,其经验可供类似工程借鉴。     

Geotechnical characteristics of Bakhtiary dam site,SW Iran: the highest double-curvature dam in the world

The Bakhtiary Hydropower Project with a 325 m high dam will be constructed on Bakhtiary River, in southwest Iran. The main dam has been designed as a double-curvature concrete structure which will be the highest one of its type in the world. Geologically, the dam site is located on siliceous limestone of the Sarvak Formation in the northwestern part of the folded Zagros. A large number of complicated geological structures in the study area, such as folding and duplex structure, faults, chevron folds, kink band zones as well as joint and fracture systems, raised concerns regarding the acceptability of the site for such a monumental dam. To create a comprehensive geotechnical model of the dam site and appurtenant structures, very extensive surface and subsurface investigations were carried out, including core drilling, water pressure testing, driving exploratory galleries for engineering geological mapping, a rock mass discontinuity survey and in situ rock mechanical tests. This research applies the results of the engineering geological and geotechnical investigations to define the geomechanical model of the dam site enabling options to be considered to achieve a safe dam design. The investigations show the rock mass of the dam site area is intersected by four main discontinuities namely, the bedding plane(s) of the rock mass and three major joint sets. Water pressure tests provide data about the permeability of the rock mass which is significantly dependant on the joint properties and the geological structures. These parameters, set the criteria for the design of the grout curtain at the dam foundation. The rock mass classification of the dam site was determined mainly based on the gallery survey and core logging using the rock mass rating, geological strength index (GSI) and Q system. Six classes of rock mass qualities were distinguished which show a fair to good rock mass at the dam foundation. From the plate load test results, a site-specific correlation was developed for estimating the modulus of deformation of the rock masses using GSI value. The estimated engineering geological and geotechnical parameters at the dam site are generally favorable and suitable for the safe design of the Bakhtiary arch dam with a height of 325 m.     

松原5.7级地震砂土液化研究

2018年5月28日吉林省松原市宁江区发生M5.7级地震,震中地区出现典型罕见的大范围砂土液化现象。通过震害现场调查,结合钻探取样、标贯试验、波速测试及静力触探等试验测试手段,查明震害情况和场地特性,初步分析此次大范围砂土液化的形成条件和影响因素。调查结果表明,此次地震液化区域面积约80km2,宏观现象主要以水稻田内表喷水冒砂为主,未造成建筑物大规模破坏,且区域内土层分布相对单一,液化分布主要受地震动、地形地貌及地下水位等因素控制;液化土层埋深主要在10m以内,并且钻探揭露一处埋深17m左右黏土层中的液化砂土上升通道,证明本次地震中出现明显的深层砂土液化现象,该现象在地震现场调查往往被忽略;静力触探在鉴别液化层位、获取土层物理力学参数上具有一定优势,较适用于震后现场调查工作。另外,松原市具有发生更大规模砂土液化的可能性,在防震减灾规划及建设工程勘察设计等项目中,对该地区的砂土液化情况需进行专门研究。     

鱼祖乍尾矿坝地震响应综合分析

地震荷载条件下坝体稳定性不足引起的溃坝事件是尾矿库的一种严重病患。本文采用不排水有效应力法对楚雄鱼祖乍尾矿坝进行了地震响应综合分析,从坝体动力反应及液化结果得出该坝在7度地震时是稳定的。但是,还应加强管理,在液化区采取加固措施。