黄河上游某电站上新统石膏夹层对坝基岩体稳定性影响评价

拟建的黄河上游某水电站在勘查过程中发现在河床以下存在一层厚约2m的石膏层。石膏岩遇水易溶解,工程地质性质较差,力学强度较低,是水电建设中的不良岩体。本文对石膏岩的物理力学性质和化学成分做了仔细分析,分析了石膏溶蚀后对坝基稳定性的影响,找出防止石膏溶蚀的判断标准,最后得出防治措施。     

Method of leakage study at the karst dam site. A case study: Khersan 3 Dam,Iran

The excellent topographic condition of the limestone canyons for dam construction may be rejected if they are karstified. Karst features cause the reservoir not to be impermeable enough to permit the water to fill it and leakage occurs and often increases with time. Moreover, karst features may involve the stability of the dam itself. A few operated dam sites at the Zagros Zone encountered a leakage problem. Furthermore, more than 30 dams are presently under study for construction in the Zagros Zone. Karst conditions and leakage potential were investigated at an under-study site (Khersan 3 Dam) for assessing the general methodology for the study of leakage potentials. Conventional methods for studying karst features, geological mapping, geomorphology and extensive borings were applied before the dam was constructed. These methods are not efficient enough to precisely reveal the karst structure, especially hidden and paleokarst, nor the hydrological behaviour of the karst structure in different settings of groundwater flow. Based on the present case study and previous applied approaches by other authors, this paper introduces a methodology by means of karst structure and functioning approaches at local and regional scales that cover the conventional methods and overcome their shortages. The proposed methodology should be applied before construction of a dam and should include three steps (a) recognition of geological and hydrogeological settings, (b) delineation and functioning of the karst system related to the future reservoir, and (c) assessment of the leakage potentials. Following this methodology, the most probable leakage zone(s) and path(s) at the dam site can be highlighted.     

人类活动影响下娘子关岩溶水系统地球化学演化

娘子关泉是我国北方最大的岩溶泉之一,也是阳泉市工农业生产和人民生活的重要供水水源。地下水地球化学演化分析表明,在地下水由补给区向排泄区运移过程中,除固有的水岩相互作用外,由于受采矿活动和地表水入渗补给的影响,岩溶水由低离子含量的HCO3-SO4或HCO3型水逐渐成为SO4型、SO4-HCO3型和SO4-HCO3-Cl型水。在泉群集中排泄区,区域流动系统与局部流动系统的地下水发生混合作用,最终形成了水质相对良好的HCO3-SO4型或SO4-HCO3型岩溶泉水。在此过程中,地下水对方解石和白云石也由最初的溶解作用演变为沉淀再结晶。尽管石膏呈持续溶解现象,但在采煤活动严重影响区域,石膏的沉淀也可能出现。地球化学模拟表明,在岩溶含水层中,地下水首先以方解石（白云石）的溶解为主;随着石膏溶解数量的增加,方解石（白云石）的溶解开始受到抑制,进而发生沉淀,石膏的溶解成为控制地下水水化学的主导过程。当矿坑水混入时,地下水相对石膏过饱和,地下水对碳酸盐岩含水介质的溶蚀能力得到增强。随着水岩反应的演进,铁氢氧化物大量沉淀,通过共沉淀和吸附作用去除了地下水中的重金属类污染物。      

水中自然电场法探测病态水库岩溶渗漏通道———以金鸡河水库一级水电站为例

在岩溶区修建的水库或矿山尾矿库等建筑物,常因库区岩溶地质条件复杂而出现库水或污水渗漏等问题,岩溶渗漏通道勘察中常用的物探方法多布置在库区的大坝、坝肩等库岸陆地一带,未能对库内的库底岩溶塌陷等岩溶渗漏通道直接进行探测与评价,致使探测与治理效果往往不佳。本文以桂北金鸡河水库一级水电站放水涵管旁岩溶渗漏通道探测为例,研究水上自然电场法探测水库岩溶渗漏通道的原理、现场工作方法及探测效果。研究区出露地层主要由泥盆系榴江组（D3l）石灰岩夹白云岩、白云质灰岩,泥盆系东岗岭阶（D2d）白云岩、石灰岩、泥质灰岩组成,隐伏岩溶中等发育。区内一级水电站放水管入水口放水可引起强烈水上自然电位负心区域场,经采用圆周平均法划分水上自然电位区域场与剩余局部异常计算,分离出6个被强烈区域场淹盖了的次级似等轴状或似椭圆状负心水上自然电位剩余局部异常。经潜水员潜水入库内查看,这6个负心剩余局部异常区在库底均有岩溶塌陷或岩溶开口或库底渗漏天窗一一对应,其中,16线46-48号测点附近出现的似等轴状负心剩余局部异常对应的库底岩溶塌陷规模最大,塌陷坑直径约1.8 m,塌陷坑深约2.5 m,其余异常区对应的库底渗漏天窗或岩溶开口规模次之。经库内外水的简易连通实验及工程地质钻探,物探异常查证效果好。水上自然电场法可用于岩溶病态库区水上应急、快速圈定浅层岩溶渗漏通道范围等岩溶地质问题调查。      

An Effective Approach to Rehabilitate Damaged Barrier System Against Piping and Contaminant Flow

The monitoring operation of an older impoundment (such as dams and waste barrier materials) during the service life of the structure cannot be overemphasized. Since older infrastructures seem to be more susceptible to piping and seepage failure, their construction design should be analyzed and monitored at places where a potential problem could occur. Once an impoundment is constructed without adequate filters layers and foundation treatments, then the prevention of piping or seepage may require an effective approach to constructing a cut-off wall to prevent eventual failure. In order to identify and understand theses failure modes, it is important to identify the physical parameters of the impoundment system, such as the zones of various soil gradations, the compaction of these zones, the hydraulic conductivity, the compatibility of the soil formations within and beneath the core or liner, as well as the cohesive and dispersive properties of soils at various location within the structure. Once these parameters are known and quantified, an adequate assessment of the structure’s susceptibility to piping or contaminant transport can be established. This type of an analysis will enable the proper design of a cut-off wall and predetermine the effectiveness of its long-term performance. The Vermont Waterbury Dam (built in 1938) is example of seepage related problem that implemented a cut-off wall design to prevent piping paths from undermining the structure. In this case, some forensic sampling had to be performed and the parameters of the soils as just mentioned were key factors in determining the wall design. In this paper, the Waterbury dam rehabilitation is investigated as case studies, in order to better understand how older designs and poor construction of impoundments can lead to piping condition in dams as well as failures in waste barrier systems. The Secant Cut-off wall (constructed at Waterbury Dam) is mentioned as a corrective measure taken for this dam and there is a brief discussion as to how this construction rehabilitation technique can be applied to waste barrier impoundments.     

Karstification below dam sites: a model of increasing leakage from reservoirs

Unnaturally steep hydraulic gradients below foundations or across abutments of dams may cause solutional widening of fractures in karstifiable rocks of carbonates or gypsum. This could cause increasing leakage which may endanger the performance of the construction. To investigate this problem recent models on natural karstification have been applied. We have performed numerical simulations of leakage below a model dam with a grouting curtain reaching down to 100 m below its impermeable foundation of 100 m width. Water is impounded to a depth of 100 m. The dam is located on a terrane of fractured rock dissected by two perpendicular sets of fractures with spacing of 5 m, and with a log-normal distribution of their initial aperture widths of about 0.02 cm. In the first state of karstification these fractures widen slowly, until a pathway of widened fractures below the grouting has reached the downstream side with exit widths of about 1 mm. This causes a dramatic increase of leakage, and turbulent flow sets in. After this breakthrough at time T, in the second state of karstification, dissolution rates become even along these fractures and cause widening of about 0.1 cm year^-1 for limestone, and at least of 1 cm year^-1 for gypsum. This leads to an increase in leakage to excessive rates within 25 years for limestone, but only 5 years for gypsum. We have performed a sensitivity analysis of breakthrough time T for the various parameters which determine the problem. The result shows breakthrough times in the order of several tens of years for both limestone and gypsum. We have also modelled leakage to caves or karst channels 200 m below the bottom of the reservoir, which could induce the formation of sinkholes. The model can be extended to more realistic settings. In conclusion, our results support the prediction that increasing leakage at dam sites can be caused by recent karstification which is activated after filling the reservoir, possibly leading to serious problems within its lifetime.     

国际大坝工程研究动态——‘95马来西亚大坝工程国际学术会议简介

笔者通过对参与’９５大坝工程国际学术会议共１２６篇论文及加拿大大坝安全协会所作的“加拿大大坝安全指南”学术报告的分析和归纳，就目前国际大坝工程研究中的大坝安全规范及管理，水电工程开发与环境保护，大坝地基处理，大坝筑坝关键技术及新型筑坝材料等五个方面的动态作了简介。     

大港探区奥陶系岩溶储层发育分布控制因素

大港探区奥陶系厚 6 0 0～ 80 0m,主要由石灰岩和白云岩组成。本区奥陶系的储层主要为岩溶储层。控制岩溶发育的主要因素有:岩性及沉积环境、水动力条件、古地形因素、断裂与裂缝发育情况和风化淋滤时间等。白云岩和石膏发育的地层有利于岩溶储层发育 ;潮坪环境是有利的储集岩发育相带。岩溶储层主要发育在距不整合面 2 0～2 0 0m范围内。加里东期古地形为南西高、北东低,水流方向是自南西向北东的 ;岩溶斜坡和不长期积水的岩溶洼地是有利的岩溶储层发育部位,尤其是岩溶斜坡。裂缝和断层发育的部位是岩溶储层有利的发育部位,裂缝和断层的走向控制岩溶带的走向。风化剥蚀时间越长,越有利于岩溶储层发育。     

Investigating sediments and rock structures beneath a river using underwater ERT

This article presents hydrogeophysical investigations performed in a well-developed, long-term hydrogeological gypsum karst research site where subsurface evaporite dissolution has led to the subsidence of a river dam and an adjacent highway; both constructed on gypsum-containing rock, southeast of Basel, Switzerland. An observation system was set up to improve the protection of surface and subsurface water resources during remedial construction measures of the highway and in order to understand the processes, as well as the temporal evolution, of rock water interaction (flow and dissolution). However, no detailed hydrogeological information beneath the river could be derived from the previous investigations. To supplement the basic knowledge on this area, underwater Electrical Resistivity Tomography (ERT) measurements were conducted in the river bed upstream of the dam. The ERT-data are interpreted together with drill-core information and a conceptual 3D-Model of the area behind the dam and beneath the river. Results help to delineate weathered zones, associated faults and the thickness of sediment deposits behind the dam, as well as to locate voids within the local karst system. The combination of the ERT and modeling allows the optimization of future site-specific remedial construction measures.     

Evaluation and treatment of seepage problems at Chapar-Abad Dam, Iran

Engineering geological properties of the ground at the Chapar-Abad Dam were investigated in order to evaluate seepage problems and to select a proper method of water-proofing prior to construction. The dam is located to the northwest of Iran and is undergoing construction phase. The geology of the site consists of a series of Early Cambrian limestones and shales that crop out on the abutments and a valley that is filled by 60 m of alluvium deposits. The presence of thick alluvium deposits with various coefficients of permeability along the foundation demonstrates a possible seepage problem after water impoundment in the reservoir. The potential of water seepage was evaluated by the study of joint systems of the rock units, the use of numerical analysis to simulate water flow in the ground, and by conducting in-situ tests to estimate the permeability's values. Based on the obtained results and by reviewing many types of water-proofing methods regarding cost, feasibility and safety factors, the installation of a grout curtain is suggested.     

磷石膏岩溶发育机理研究及工程处理

磷石膏可以直接为水所溶蚀,磷石膏的特殊结晶形态以及其中的杂质进一步影响磷石膏的溶解特性,从而产生磷石膏的岩溶现象。堆放在碳酸盐岩地区的磷石膏由于复合岩溶作用的影响,还会带来水文、工程地质等方面的问题,磷石膏的岩溶现象是影响渣场稳定、渣坝稳定、地下水环境的特殊问题。提出了提高磷石膏渣坝稳定性、防止磷石膏渣场渗漏和保护地下水环境的工程措施。     

Construction of grout curtain in karstic environment case study: Salman Farsi Dam

Salman Farsi is an arch-gravity dam. It is 125 m high and located on the Ghareh-Agaj River in Fars province, south of Iran. From the geological and hydrogeological point of view, this dam is one of the most complicated sites in Iran. Existence of 40 springs at the river level (including hot springs), and many faults and crushed zones are part of these complications. The dam site is famous for its numerous big caverns. Main characteristics of the rock mass are: (1) low permeable limestone of moderate to high strength, (2) high karstification generally localized around intersection of faults or discontinuities. The main purpose of grout curtains is to change the hydrogeological characteristics (reducing the permeability) of the rock mass. Constructing a grout curtain in a karstic environment with a high random distribution of karst features contains some uncertainties and surprises cannot be excluded. During the excavation of grouting galleries, some big caverns at both abutments were discovered. The volume of the biggest one (Golshan’s Cave) exceeds 150,000 m³. A large-scale underground geotechnical treatment is needed to improve the water tightness of the dam site.     

莲花台水电站岩溶发育特征及工程意义

根据地质调查和勘探资料,阐明莲花台水电站坝址区岩溶发育形态、规模及空间展布特征,归纳岩溶发育规律。结果表明:坝址区岩溶发育主要受岩性和地质构造控制,岩溶现象分布范围广,岩溶发育较为密集,具有垂向分带性及空间分布不均匀性的特征;岩溶发育对工程的影响主要表现在岩溶渗漏和岩溶塌陷稳定问题两个方面,岩溶渗漏可能造成电站无法达到设计正常蓄水水位,岩溶空间的存在可能引起坝基抗滑稳定问题。因此,建议设置防渗帷幕,并对坝基开挖揭露的溶洞进行换填加固及固结灌浆等工程处理措施,通过处理,可有效避免岩溶发育对工程的影响。      

GIS and ANN coupling model: an innovative approach to evaluate vulnerability of karst water inrush in coalmines of north China

Evaporites, including rock salt (halite) and gypsum (or anhydrite), are the most soluble among common rocks; they dissolve readily to form the same types of karst features that commonly are found in limestones and dolomites. Evaporites are present in 32 of the 48 contiguous states in USA, and they underlie about 40% of the land area. Typical evaporite-karst features observed in outcrops include sinkholes, caves, disappearing streams, and springs, whereas other evidence of active evaporite karst includes surface-collapse structures and saline springs or saline plumes that result from salt dissolution. Many evaporites also contain evidence of paleokarst, such as dissolution breccias, breccia pipes, slumped beds, and collapse structures. All these natural karst phenomena can be sources of engineering or environmental problems. Dangerous sinkholes and caves can form rapidly in evaporite rocks, or pre-existing karst features can be reactivated and open up (collapse) under certain hydrologic conditions or when the land is put to new uses. Many karst features also propagate upward through overlying surficial deposits. Human activities also have caused development of evaporite karst, primarily in salt deposits. Boreholes (petroleum tests or solution-mining operations) or underground mines may enable unsaturated water to flow through or against salt deposits, either intentionally or accidentally, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures can cause land subsidence and/or catastrophic collapse. Evaporite karst, natural and human-induced, is far more prevalent than is commonly believed.     

陆浑水库坝基断层破碎带渗透稳定性评价

陆浑水库位于河南省洛阳市嵩县境内。为了论证大坝在水库投入正常高水位（319．5m,327.5m,331.8m)运行时的安全，经过对30余年的水位观测资料的整理和分析，在厘定水文地质模型的定性分析基础上，运用现代数理统计原理，成功地解决了困扰水库正常运行的坝基渗流问题，获得了善于坝基渗透稳定状况及其变化趋势的认识。结果表明：目前大坝的运行状况是正常的；水库在缓慢蓄水过程中，截水槽的薄弱部位可以得到渗透中固，截水槽中的填土与岩石结合面的抗渗比降可达45以上；上游铺盖与截水槽结合下游排水的防渗体系有效地控制了坝基渗流。同时，预测了高水位时坝基渗流是稳定的，水库完全可以投入高水位运行。这为病险水库的论证提供了一个案例。     

某大型水电枢纽坝基埋藏型岩溶发育特征及深层承压水研究

作者在现场工程地质勘察、试验基础上, 对我国西南某大型水电枢纽坝基所遇特殊的复杂埋藏型岩溶、承压水问题进行了研究, 弄清了坝基岩溶、承压水形成条件及发育特性, 对坝址选择及工程处理的决策具有重要意义。     

Changes to dam safety management in British Columbia triggered by failure of a small earth dam

The Testalinden earth dam in southern British Columbia failed in June 2010 and created a huge debris flow. Homes were destroyed and property was damaged. The failure of this small dam resulted in a comprehensive review of over 1000 dams in the province, evaluation of dam safety management practices, changes to the Water Act and improvements in how data on dams are collected, archived and communicated. The provincial dam inventory was re-evaluated to ensure that appropriate consequence classification, and therefore attention, is assigned to dams. Increased scrutiny was placed on dam owners to ensure they complied with dam safety policies and to ensure they submitted annual inspection reports and formal dam safety reviews in a timely manner. Dam owners and professionals engaged in dam safety activities have received new guidelines and better education and training.     

Subsidence hazards due to evaporite dissolution in the United States

Evaporites, including gypsum (or anhydrite) and salt, are the most soluble of common rocks; they are dissolved readily to form the same type of karst features that typically are found in limestones and dolomites, and their dissolution can locally result in major subsidence structures. The four basic requirements for evaporite dissolution to occur are: (1) a deposit of gypsum or salt; (2) water, unsaturated with CaSO₄ or NaCl; (3) an outlet for escape of dissolving water; and (4) energy to cause water to flow through the system. Evaporites are present in 32 of the 48 contiguous states of the United States, and they underlie about 35–40% of the land area. Karst is known at least locally (and sometimes quite extensively) in almost all areas underlain by evaporites, and some of these karst features involve significant subsidence. The most widespread and pronounced examples of both gypsum and salt karst and subsidence are in the Permian basin of the southwestern United States, but many other areas also are significant. Human activities have caused some evaporite–subsidence development, primarily in salt deposits. Boreholes may enable (either intentionally or inadvertently) unsaturated water to flow through or against salt deposits, thus allowing development of small to large dissolution cavities. If the dissolution cavity is large enough and shallow enough, successive roof failures above the cavity can cause land subsidence or catastrophic collapse.     

The Lar Dam; an example of infrastructural development in a geologically active karstic region

The problems associated with the construction of the Lar Dam, Iran, provide a classic example of problems that can result from infrastructural development in an active geological terrain which includes the regional carbonate units. The Lar Dam lies in a heavily faulted and fractured region close to the active Damavand volcano. The fracturing has enhanced the production of karst and sinkholes in the limestone below the dam, and acidic ground-water run-off from the Damavand volcano increases the dissolution of the carbonate beds along the fractures to produce sinkholes below the dam. The initial problem of building the dam in such a region is compounded by the relationship between water loss due to enhanced sinkhole development and the remedial measures being taken to lessen this leakage. Drainage of the sub-reservoir caverns through leakage along fractures can lead to loss of hydrostatic support for the developing sub-reservoir caverns, and their consequent collapse. Furthermore, rapid changes in subterranean water levels would lead to rock-shattering hammer effects particularly during rapid rises in water level.     

余震作用下堰塞坝体破坏及溃决过程大型振动台试验研究

山区特大地震往往导致大量堰塞湖,例如2008年汶川地震形成了至少257个堰塞湖,并且主震后发生了大量余震,这些余震可能会影响堰塞坝体的安全状态。通过大型振动台模型试验,研究了余震及库水耦合作用下堰塞坝体的破坏及溃决机理和过程。共进行了两组不同材料的振动台模型试验,分别模拟含黏粒较多且颗粒较小（坝体Ⅰ）和基本不含黏粒且颗粒较大（坝体Ⅱ）的两种坝体。在不同水位条件下进行振动台试验。研究成果表明:（1）地震和库水耦合作用下堰塞坝体的主要溃决方式是漫顶溢流,主要溃决过程为地震力使松散的堰塞坝体发生沉陷,库水渗入使沉陷加剧,最终水位上升漫过坝顶发生溢流冲蚀破坏。（2）地震一般不会直接引起堰塞坝体的破坏。地震力对坝体稳定性的主要影响是使坝体发生沉陷变形。在地震和库水耦合作用下,坝体沉陷比单一因素作用下更为剧烈,因此地震作用会使漫顶溢流提前发生。（3）地震和库水耦合作用下坝体Ⅰ沉陷量大于坝体Ⅱ,说明现实中由大粒径岩土体组成的堰塞坝体具有更好的稳定性。