【作者】 田启文；

【导师】 靳孟贵；

【作者基本信息】 中国地质大学 ， 水文学及水资源， 2014， 博士

【摘要】 坪头水电站是四川省美姑河“一库五级”开发方案最下游的一个梯级电站。美姑河是金沙江左岸的一级支流,坪头水电站地下厂房又在金沙江溪洛渡水电站水库回水范围内。坪头水电站采用闸坝引水式开发,最大闸坝高38.5m,库容62.09万m3,左岸引水隧洞长12.7Km,利用水头298m,地下厂房布置三台机组,装机容量共180MW。该电站厂址区位于美姑河左岸,距闸址区23km,其上游以尔古沟为界,下游以龙头沟为界。地下厂房区位于龙头沟上游0.5-1km,主要水工构筑物有压力管道下平段、地下厂房、主变室、尾水洞等。该区的水工构筑物置于水平埋深10-465m,垂直埋深5-325m范围内的山体里,围岩为震旦系灯影组白云岩,岩溶裂隙发育。原设计方案中压力管道下平段、地下厂房、主变室、尾水洞底板高程分别为573.8m、569.3m、587.7m和570.8m,除主变室外,其他洞室底板高程均低于当地的地下水位(583-587m)和美姑河河水位(580.24m)。将来金沙江溪洛渡水电站建成水库蓄水至600m高程后,受溪洛渡水电站水库回水影响,坪头水电站厂址区段内的美姑河河水位将抬升至600m高程,厂址区山体内的地下水水位将整体雍高,地下水水位将高于地下厂房区内所涉及的各水工建筑物洞室的底板高程。显然,地下厂房区内各水工构筑物在施工开挖和运行过程中,都会出现地下水和美姑河河水或溪洛渡水电站库水倒灌洞室的涌水问题。因此,要保证坪头水电站厂房区内各水工构筑物的正常施工和电站运行安全,地下厂房等洞室在施工期和运行期的防渗设计非常关键。由于坪头水电站厂址区位于震旦系灯影组白云岩岩溶水系统的排泄区,如何构建厂区正确的水文地质概念模型和仿真度较高的数值模拟模型,模拟预测不同工况条件下的地下水渗流场特征及硐室涌水量是本项目遇到的挑战。为了指导工程厂址区水工构筑物的合理布置和防渗方案的科学设计,保障工程的安全施工和正常运行,通过调查、勘探、各类试验、定性和定量分析,本文主要完成了以下研究工作：(1)研究区水文地质条件和地下水系统分析：(2)岩溶裂隙发育规律研究及典型单元体大小的确定；(3)非均质各向异性三维渗流数值模拟模型的构建；(4)不同工况的施工过程和运行期渗流场特征、涌水量的模拟预测和对比分析,提出了优化的工程布置和防渗方案。取得以下主要成果和结论：1、坪头水电站厂址区位于龙头沟岩溶地下水系统的集中排泄区,该系统汇水面积约46kmm2,含水系统面积为12km2。天然条件下,地下水主要来自山区降水入渗补给,自北向南径流、向厂址区汇聚,最后以泉群的形式集中排泄于美姑河。原设计方案厂房区水工构筑物存在严重的涌水问题,常规施工中不仅会截断龙头沟地下水系统的排泄途径,而且将诱发美姑河河水的倒灌补给。根据实测涌水量及趋势推测,平水期洞室涌水量为0.38m3/s、洪水期洞室涌水量将增至约1功3/s、溪洛渡水库正常蓄水位600m时的洞室涌水量将达5.9m3/s,存在极大的工程隐患。2、厂址区水文地质调查和裂隙发育规律研究表明：(1)厂址区裂隙发育,已形成连通性较好的裂隙网络系统,有一定程度的溶蚀作用,为溶隙-裂隙型含透水介质。(2)受地层岩性和地质构造控制含水介质渗透性表现为明显的非均质各向异性；其中非均质性主要受地层岩性的控制,厚层细晶白云岩裂隙的延展性和张开性较好,渗透性相对较强,而薄层细-微晶白云岩裂隙的延展性和张开性较差,其渗透性相对较弱。各向异性主要受裂隙发育方向控制,尤其受延展性和张开性较强的层面裂隙控制,渗透性呈现出北东向明显强于北西方向,两者渗透系数相差约1.5倍。(3)含水介质渗透性随深度增大而逐渐减弱,厂址区钻孔和压水试验成果显示：480m高程以上,岩体裂隙、岩溶发育,压水试验获得的渗透率一般大于3Lu(吕荣)；450-480m高程,岩体裂隙较发育,但基本已无溶蚀现象,压水试验一般在1～3Lu(吕荣)；450m高程以下,岩体裂隙不发育,可以视为相对隔水层。3、通过地下厂房顶层排水廊道(610m高程)裂隙的系统测量和统计计算发现,本区裂隙含水介质的渗透性存在尺度效应。同一测点,当研究尺度较小时,裂隙率呈现随尺度变化而变化的特点,但随着尺度增大到一定尺度后,裂隙率基本趋于稳定,而且不同测点裂隙率达到基本稳定的尺度相差不大,一般在2.5-3.5m。据此,确定后续采用裂隙连续介质模型,刻画渗流场的典型单元体尺度为3.5m,为数值模拟单元剖分提供了依据。4、构建了适合本区条件的裂隙岩体三维非均质各向异性连续介质的概念模型和水流数值模型。通过对比国内外各种裂隙介质模型的优缺点,结合本区水文地质条件和裂隙发育特征,认为采用三维非均质各向异性连续介质模型刻画研究区的渗流场较为适合。通过详细的裂隙测量、流场分析、示踪试验、钻孔压水试验等综合技术方法,深入研究了模型边界条件、水文地质参数分区、渗透系数初值等,确保了模型的合理性。针对基岩山区地下水埋深大、难以开展地下水抽水试验的情况,利用已开挖的硐室开展水位恢复试验,获得了地下水位回升曲线,为地下水数值模型的反演识别获取了更多资料,大大提高了模型的仿真度。5、建立了厂房区水工构筑物原设计方案和拟调整抬高方案的不同防渗方案的数值模拟模型,模拟预测了50种工况的地下水渗流场特征及涌水量。包括不同边界条件,如美姑河水位在平水期、丰水期以及将来溪洛渡水库蓄水运行期的三种情况;施工期不同防渗条件,如沿美姑河局部防渗和整体防渗；运行期地下厂房的五种不同防渗帷幕深度情况；从水文地质角度提出的厂房整体就地抬升15m后的各种工况,全面展现了本工程可能出现的45种工况条件下的地下水流场特征和涌水量情况。6、基于上述各种可能工况的地下水流场和洞室涌水量预测结果,从水文地质角度对各种工况防渗帷幕工程实施的可行性及工程量,进行了全方位对比分析与优化,认为：厂房整体抬高方案的施工和运行更加安全可靠,工程建设过程和运行情况已充分证实了这个方案的可行性和合理性。坪头水电站厂房区构筑物原设计方案无论是施工期,还是运行期都存在严重的涌水问题。施工洪水期涌水量可高达76882m3/d,由此引起的渗透稳定问题十分严重,必须在美姑河沿岸及地下厂房周边(在平面上和剖面上)都实施全封闭的防渗帷幕工程,工程量和施工难度都非常巨大。全封闭防渗帷幕的深度将达160m,而本区不具备设置多层灌浆廊道的施工条件,加之本区白云岩裂隙含水介质具有沿裂隙岩溶“砂化”的特点。该类防渗帷幕工程施工难度极大,工程质量难以保证,存在较严重的工程施工和运行的安全隐患。提出地下厂房构筑物整体抬高15m的设计方案。根据对地下厂房整体抬高方案各种工况地下水渗流场数值模拟结果的对比发现,地下厂房抬高15m以后,绝大多数构筑物都提高到天然地下水位以上,即使有些工况条件下仍有洞室涌水问题,但涌水量大大减小(施工时洪水期涌水量为14456m3/d),工程施工条件得到了大大改善。运行期间虽然由于溪洛渡水库蓄水后仍有涌水问题,但此时地下厂房底板已经完成,可以通过加强厂房基础的抗渗设计标准来减轻运行期的防渗压力。总之,本次研究是针对工程建设中实际遇到的难题,从工程实际出发开展了一系列行之有效的研究和勘察与试验工作,很好地将地下水系统理论、数值模拟技术与工程实际有机结合。不仅解决了本工程的实际问题,同时对类似工程也有重要参考价值。此外,坪头水电站最终采纳了本次研究的结论和建议,对厂址区各水工建筑物的结构支护处理措施和防渗工程进行了优化设计。目前坪头水电站已正常发电两年多,运行情况良好。本文的特色与创新之处主要为：(1)通过裂隙网络测量和渗流场研究,发现研究区裂隙含水系统具有连续介质的特征,其等效连续介质的典型单元体尺寸为3.5m,为采用等效连续介质模型建立地下水数值模型以及剖分尺度提供了理论依据。(2)利用支洞排水工程,开展地下水水位恢复试验,获取水文地质参数和模型识别的资料；为类似陡峻岸坡山区,不具备抽水试验条件的地下洞室工程获取水文地质参数和模型识别提供了新的思路和方法。(3)运用地下水数值模拟方法进行大量(50种)工况模拟,优化设计地下工程及其防渗方案,解决了复杂条件下的工程难题。更多还原

【Abstract】 Pingtou Hydropower Station is located on Meigu River, which is a first level tributary of Jinsha River, in Liangshan Sichuan province. It is the last cascade hydropower station of "One-reservoir and five-cascade" development plan in the downstream. The underground powerhouse of Pingtou Station perches in the backwater area of Xiluodu Hydropower Station on the Jinsha River. Pingtou Station is a kind of dam-diversion power station, with the height of sluice gate38.5m and a storage capacity of620900m3. Its left diversion tunnel is12.7km long with an available water head298m, combined with three sets of machines underground, the installed capacity reaches to180MW. The station site23km far away from the dam is built on the left bank of Meigu River, which reaches the Ergu Valley upwards and Longtou Valley downwards. The underground site located at0.5～1.0km up the Longtou Valley, consists of lower horizontal section of pressure pipes, underground powerhouse, transformation room and tailrace tunnel. Hydraulic structures lie at the depth of10-465m laterally and5-325m vertically in the rock blocks, with Dengying Formation of Sinian dolomite as wall rock which causes great development of karstification and fractures. According to the original design, the base surface heights of pressure pipes, underground powerhouse, transformation room and tailrace tunnel are573.8m,569.3m,587.7m and570.8m, respectively. Except the transformation room, all of the structures are lower than the water level of local groundwater and Meigu River,583-587m and580.24m, respectively. However, as the Xiluodu Hydropower Station is completed, the level of the reservoir would stay at600m a.s.l. to generate electricity; the water level of Meigu River in the site region, influenced by the backwater of the reservoir, will rise to600m too, higher than the base surface levels of structures. Thus, it will cause drain water of groundwater and Meigu River back up into the chambers during the excavation and construction of structures, obviously. To undertake the construction and operation of the hydraulic structures in the underground site area, the anti-seepage preventions of the chambers underground should be the key and treated seriously.Because the site situates at the drainage area of karst system formed by the Dengying dolomite, it is a challenge to construct the hydrology conceptual model and numerical model with high degree of simulation, which could better predict the characteristics of the groundwater seepage system and the amount of chamber gushing under different operating conditions.To instruct the application of hydraulic structures properly and design the project of conservancy construction (anti-seepage prevention), hydrological investigation, geological exploration, related experiments and quantitative and qualitative analyze were carried on. The following works were finished to ensure the project under security construction and functioning well:(1) Hydrological conditions and the groundwater system of the research area were analyzed;(2) The regularity of karstification and fractures development were evaluated and the Representative Elementary Volume was defined;(3) A3-D heterogeneous anisotropy numerical simulation model was constructed;(4) The optical application of project and anti-seepage prevention schemes were proposed through simulating the characteristics of seepage field and the amount of water gushing under different operating conditions and courses. It concludes as follows:Firstly, Pingtou Hydropower Station is located in the main discharge area of the karst groundwater system originating from Longtou Valley, with a water catchment of46Km2area and an aquifer system of12Km2. Naturally, the groundwater receive recharge through infiltration of precipitation, then flows North to South and sinks at the structures sites, discharges to the Meigu River as fountain groups finally. There were severe problems of water gushing in the hydraulic structures, which would block the discharge routine of the Longtou Valley groundwater system and induce backwater of Meigu River during daily construction, according to original design. Thus, the amounts of water gushing were measured through experiments and a tendency was acquired for further prediction:the chamber water flux could reach to0.38m3/s at normal water level, and then increase to1m3/s and5.9m3/s during flood season and the period when the level of Xiluodu reservoir stayed at600m, respectively.Secondly, the investigation of hydrological conditions and the regularity of fracture development in the site area reveal that:(1) Fracture network was formed by the finely connected fractures, and caused corrosion effect to an extent in the site area. It could be solution-enlarged fracture-fracture media.(2) The media of aquifer controlled by the lithology and tectonism behaves as heterogeneous anisotropy medium. Heterogeneity of medium is influenced by the lithology:with better extensibility and expansibility, the permeability of thicker fine dolomite is larger than that of the thin microcrystal dolomite. The anisotropy is controlled by the fractures direction, especially affected by the strata fracture with better extensibility and expansibility:the permeability becomes weaker from northeast to northwest differing from1.5times.(3) The permeability of the aquifer decreases with the depth increasing vertically. The lithology of the borehole and results of water-pressure test in the site show as follows:Above480m a.s.l., fractures and karstification of the medium are well-developed with permeability larger than3Lu (according to Lv Rong); below450m a.s.l., the medium could be aquiclude with fracture of medium merely-developed; between450m and480m a.s.l., the permeability ranges from1to3Lu with fractures developed but no corrosion effect on the medium.Thirdly, through the systematically measurements and statistical calculations of the fractures on the top drainage gallery (610m a.s.l. high) of the underground powerhouse, this study illustrates the existence of scale effect of the fracture aquifer medium. For the same point, the fracture rate shows the characteristics of the spatial variation when the scale is small, while the fracture rate tends to be stable when the scale increases to a certain extent. Moreover, the certain stable scale of different measurement points is basically at a range from2.5m to3.5m. This work provides the possibility for using continuous model depicting the characteristics of seepage field in groundwater, and provides the basis for determining unit subdivision size by numerical simulation of continuous medium model.Fourthly, the3-D heterogeneous anisotropic continuum of fracture medium conceptual model and the numerical model of water-flow are suitable for this research area. By comparing the advantages and disadvantages of various fissure medium models, given the investigations of the hydrogeological conditions and the fracture site media development features, It is considered that the fractured medium3-D conceptual model is more suitable for the study area. Through the fractures on site measurement, the groundwater flow field analysis, groundwater tracer test, drilling pressure water test method, we carried out in-depth and meticulous research to identify the boundary condition, hydrogeological parameters partition, hydraulic conductivity determination of initial values etc., which ensure the rationality of the model. Considering the water level of base rock groundwater, and the difficulty in carrying out the groundwater pumping test, we make full use of the engineering condition to take groundwater level recovery test, and acquire the recovery curve of groundwater level for this site. Then as the objective function, the model is reversed to identify the groundwater numerical model, which greatly improves the model simulation, and lays the reliable geological basis for the prediction of subsequent groundwater numerical model.Fifthly, different numerical models for anti-seepage prevention scheme and the proposed adjustment scheme of the underground hydraulic structures are constructed, which could simulate the groundwater flow field and water outflow under45kinds of construction conditions. Three boundary conditions, such as the Meigu River at normal and flood water level period, respectively, and future operation period of the Xiluodu Reservoir Impoundment, are taken into consideration; different seepage conditions during construction, such as along the Meigu River local and whole anti-seepage prevention projects, five kinds of anti-seepage curtains depth underground powerhouse during operation period can be applied; if the whole bottom elevation of structures are raised by15m, various situations from hydrogeological points are put forward with, which represent the groundwater flow field under50kinds of working conditions. Groundwater seepage under various conditions could also be calculated, which can depict the characteristics of groundwater flow field and simulate each chamber water outflow.Sixthly, based on the prediction of groundwater flow field and chamber water outflow, probability and quantity of anti-seepage curtain engineering under various conditions are evaluated and optimized owing to the hydrogeological conditions, and conclude as follows:it is more safe and reliable to carry on the scheme when the overall elevation of building structures rises to15m. The feasibility and rationality of this solution has been fully proved during the engineering construction and operation period.During both construction and operation period, there is a big problem of water gushing in the original design for Pingtou hydropower station. In construction period, the flood flux can be as large as76882m3/d, which may cause a serious problem of seepage stability. Thus, enclosed anti-seepage curtains along the Meigu River and around the plant area (both in plane and section) are needed. However, the engineering quantities and construction difficulties are enormous. Full enclosed curtain depth will reach to160m, while the region does not satisfy the conditions to set multi-layer Grouting Gallery. What is worse, the dolomite fractured aquifer medium has a feature of "Sandy" along the fissures. It is difficult to carry out the engineering and the quality is hard to be guaranteed. There are more serious security risks during construction and operation period.A design that the overall elevation of plant structures should be raised by15m is proposed. According to the comparison of numerical simulation results of seepage field, after raising the elevation, most structures are built above the normal water level. Though there are still water gushing problems in some chambers under some conditions, the volumes greatly decrease (a14456m3/d flood outflow during construction period) and construction condition has been greatly improved. Even if water gushing problems exists due to the storage of Xiluodu Reservoir during operation time, the safety risks during construction period will be lowered with the completed station floor and strengthening standards of structures impermeability,In conclusion, this study is to solve the actual problem of engineering. A series of effective research, exploration and test work were carried out, and combining the groundwater system theory and numerical simulation technology with engineering practice commendably was adopted for analyzes. Its aim is not only to solve the practical problems of this project, but also the conclusions may have important instructive value for similar projects. In addition, Pingtou hydropower station has adopted the conclusions and suggestions of this study and made optical design for structures supporting measures and anti-seepage prevention engineering. Currently, the station has been generating electricity normally for more than two years and running under good conditions.The main characteristics and innovations of this paper are as follows:(1) Through the measurement of the fracture network and the study of groundwater flow field, we find that fracture aquifer system in this area has characteristics of continuous medium. The REV of the fractured rock size is determined as3.5m, which provides theoretical basis for achieving groundwater numerical simulation and ensuring the mesh scale.(2) Drainage projects of the tail water to develop groundwater level recovery tests were developed, which provided technical support for obtaining hydrogeological parameters and model identification. It also provides a new idea which would acquire hydrogeological parameters and identify models for the similar steep and precipitous mountain area, where pumping test couldn’t be carried out in underground chambers.(3) To optimize the design of underground engineering and its seepage control scheme, the groundwater numerical simulations of fifty different scenarios were used to solve the problems encountered in engineering practice under complex conditions.更多还原