金沙江其宗水电站高堆石坝建设

我国西部地区水能资源丰富,建设大型水利枢纽工程,开发西部山区的水能资源,已成为保证国民经济持续、稳定发展和缩小东西部差距的关键措施之一。但西部地区,尤其是西南山区水利枢纽的建设场地多处于地质条件复杂、岩土体工程特性不良的地质环境,水利建设存在着如何适应复杂场地的适宜性问题。拟建的金沙江其宗水电站坝址区地质条件复杂,工程开挖边坡高度大,地下洞室密集,河床覆盖层厚度大,采用高心墙堆石坝方案及其配套建筑物存在的主要工程地质问题包括坝址区千枚岩边坡、洞室的稳定性问题与坝址区河床深厚覆盖层的工程特性问题。本文针对其宗水电站坝址主要工程地质问题,以千枚岩与河床深厚覆盖层的工程特性研究为核心,从工程地质角度,评价该水电站建设高堆石坝的适宜性,同时在千枚岩与深厚覆盖层的理论研究与工程运用方面取得了一定的认识。论文主要工作与成果包括:(1)论文将千枚岩岩石微结构特征、微观破裂机理分析与岩体结构特征研究相结合,采用以各向异性特征分析为核心的研究方法,取得了千枚岩工程特性的规律性认识。在此基础上,运用多种手段对千枚岩工程边坡与洞室的失稳模式与稳定性进行研究,探讨在千枚岩中进行大面积人工高边坡与大型地下洞室建设的适宜性。同时,论文系统分析和总结了我国西部水电工程河床深厚覆盖层的工程特征,丰富和发展了河床深厚覆盖层的成因类型,形成了河床深厚覆盖层建坝适宜性评价的技术与方法。(2)通过坝址区工程地质条件调查,掌握坝址区千枚岩空间分布特征及变化规律,初步建立了千枚岩的微观结构形态、微观破裂机理与矿物成分之间的关系。千枚岩岩石矿物成分与微观断裂机理分析结果表明:一般绢云母与绿泥石含量高的岩石具鳞片变晶结构,片理面发育,千枚状构造或定向构造特征明显,在外力作用下易产生剪破裂。而石英含量较高的千枚岩,其微观结构呈现细粒状,多形成微观脆性破裂形态,在外力作用下往往产生拉破裂。(3)通过一系列岩体物理力学试验研究,重点分析了性状差别较大的绢云母千枚岩与硅质板状千枚岩的各向异性特征,指出千枚岩的各向异性特征的评价应基于岩石强度相对于定位角的变化,采用各向异性率定量评价各向异性的程度,提出千枚岩应区别于传统意义上的软岩的观点。在此基础上,选取有代表性的试验数据,与相关的千枚岩环境条件下的工程进行类比研究,总结其宗水电站千枚岩的工程特性,提出岩体物理力学参数的建议值,为准确分析工程边坡与地下洞室围岩的稳定性提供依据。(4)根据其宗水电站水工建筑布置方案,采用室内数值模拟的方法,选择了坝址典型的工程边坡与地下洞室群进行变形稳定性分析,模拟工程建设后边坡与洞室岩体的应力与变形的特征。提出其宗水电站坝址千枚岩强度相对较高,在其范围内开挖工程边坡产生坡体整体失稳的可能性很小,千枚岩具备大面积开挖的地质条件。但洞室的开挖受岩体各向异性特征的影响较大,目前水工设计的洞室轴向对洞室围岩的稳定是不利的,须合理布置,加强支护。(5)通过对坝址河床深厚覆盖层的组成及空间分布特征的研究,论文建立了坝址区覆盖层的空间形态与结构关系,进一步发展了河床深厚覆盖层成因的理论研究。论文提出河床深厚覆盖层的形成,适宜的地质环境是先决条件,复杂的区域构造演变、区域第四系气候和河谷形成演化历史是根本原因。深厚覆盖层是在地质构造运动和气候变化共同作用下形成的,气候因素占主导地位。覆盖层下部的冲积和冰水堆积并非形成于现代,河床深厚覆盖层的成因复杂,并非由单一的河流冲积物组成,其主体应是末次冰期间冰段河谷的产物,覆盖层之所以深厚,是因为存在非河流成因堆积物的加积作用的结果。从目前深厚覆盖层建坝的工程经验分析,其宗水电站坝址河床深厚覆盖层的物理力学参数与西部其它水电工程的取值相差不大,其粗粒土具有干密度较大,承载力较高的优势,坝基覆盖层的工程特性符合建高堆石坝的力学条件。(6)通过对坝址河床深厚覆盖层的稳定性计算与分析认为,坝址覆盖层深厚,以粗颗粒的卵砾石层为主,组织结构较密实,具有较高的强度,坝基产生浅层或深层滑动的可能性较小;但是,坝址覆盖层中③-1层和①层由粗粒土组成,渗透系数较大,具备发生管涌的条件;③-2层、②-2层以砂土及粉砂土为主,而②-1层夹细砂,这些部位具备发生流土的条件,坝基整体渗透变形问题比较突出;另外,坝址覆盖层中③-2层、②-2层数目众多的砂层透镜体,其厚度变化较大,埋深不一,强度相对较低,不但坝基不均匀沉降问题较严重,而且坝基承载力与液化问题也比较突出。(7)其宗水电站坝址地形条件对布置当地材料坝较为有利,经合理布置并加强支护,右岸横向山梁具备修建大型开敞式溢洪道、引水、泄洪、导流隧洞和地面厂房的条件;覆盖层坝基整体稳定性较好,但存在渗透变形、不均匀沉降和浅部砂层液化问题。建议挖除浅部砂层透镜体,对坝基土体进行加密、固结灌浆与夯实等措施。经妥善处理后河床覆盖层具备修建高心墙堆石坝的工程地质条件,坝址修建高心墙堆石坝是适宜的。本论文的研究成果达到了高坝建设适宜性工程地质研究的目标,在千枚岩各向异性的力学特征、河床深厚覆盖层的成因、工程地质特性等方面取得了一定的理论成果与规律性认识,对在千枚岩地区开挖大型工程边坡与地下洞室及高山峡谷区深厚覆盖层上建高坝、大库的工程地质理论与实践均有着指导意义。
工业羊毛毡
There are plenty of hydroenergy in west China to be exploited. It is an important strategy to accelerate economic development of west China by exploiting hydroenergy in mountain area. However, hydropower station in west China, especially south west China, are mainly located in high mountain and canyon with complex geological condition and worse character of rock and soil mass. As a result, the suitability of the geological environment for the hydro-junction becomes one of the key engineering geological problems. There are some characters including complex geological condition, thick deposits under the bed river, high artificial slopes, and plenty of caverns at the planed Qizong hydropower station. The dam of this hydropower station is designed to be high core rockfill dam. The main engineering geological problems includes instability of phyllite rock slopes and wall rock of caverns, and the engineering character of deep and thick deposits under bed river. In this paper, the engineering characters of phyllite rock mass and deep-thick deposits are studied to discuss the treatment of the main engineering geological problems. The suitability for construction of high rockfill dam is evaluated by engineering geological method, and some cognition is obtained in the study on theory and application of phyllite and deep-thick deposit.(1)In this paper, microstructure of phyllite, micro-fracture mechanism and rock mass structure are studied synthesized to acquire the regularity of engineering character of phyllite by analysis on aeolotropy character. Then, the stabilities of engineering slopes and gaverns in phyllite are studied by several methods, and the suitability for construction of engineering slopes and huge caverns in phyllite is discussed. In addition, the engineering character of deep-thick deposits lied under bed river in west China is generalized and analyzed systemically which add new origin types for deep-thick deposits, and the technique of suitability evaluation for construction of dam on deep-thick deposits lied under bed river is proposed.(2)According to the investigation of geological conditions of the dam area, the spacial distribution and variation of phyllite are discovered, and the composition and microstructure characteristics of rock is studied, and the types of rock mass structure and the development of discontinuities are summarized. The composition and micro-defects of the phyllite are discovered. The achievements have a guiding role in the research of engineering-mechanics characteristics of phyllite and analysis of the stability of cavern and rock slope.(3) The anisotropy of sericite phyllite and siliceous phyllite are analyzed by series of physical and mechanical tests, which indicates that the anisotropy of phyllite is mainly reflected in the velocity of sound wave, uniaxial compression strength, triaxial compression strength, and shear strength. Qualitative evaluation of anisotropy of the rock is based on the shape of response curve of rock anisotropy, that is how the rock strength varies by the orientation angle. The anisotropy ratio is advanced to evaluate the anisotropy of phyllite, and the most influence of anisotropy on the rock strength was to uniaxial compression strength. Then, the engineering geological character of phyllite is summarized and the proposed value of physical and mechanical parameters of rock mass is put forward, according to test data and engineering geological analogy. These parameters are the basis of stability evaluation of engineering slope and underground cavern.(4)According to the layout of the hydraulic architecture of Qizong hydropower station, some typical phyllite slopes and phyllite caverns are selected to analyze their stabilities by numerical simulation method. The distribution of stress and deformation of the slopes and caverns are studied under excavation. This study indicates that: 1)the rock mass strength of phyllite at Qizong hydropower station is high, and the whole engineering slope is stable, 2) the instabilities of caverns are influenced by the anisotropy of the phyllite, and the designed axial of the caverns put the stability of wall rock at a disadvantage. As a result, some suggestions such as reasonable arrangement and strengthening supporting can make the right bank meet the requirements of the layout of hydraulic architecture.(5)In this paper, the relationship between spacial distribution and structure of the deposits at the dam area is studied. And conclusion is obtained as follow: 1) The origin of deposits of the riverbed at the dam area is complex. The deposits include boulder and glaciofluvial accumulation of block stone and reduced stone of Late Pleistocene epoch, deposit formed by mudflow, diluvium and circulation flow, and accumulation of sand, boulder, reduced stone with silty clay interbedded and silt. 2) The deposits are with high thickness, better stratum, better water permeability, low compressibility, high mechanics strength and high bearing capacity. 3)The most important layer to dam is the lenticle sand seam in the boulder and gravel stratum, which is with little thickness, discontinuity, middle water permeability, middle compressibility, low mechanics strength, and low bearing capacity. According to the existed dam engineering experience in the deep and thick deposits, the physical and mechanical parameters of the deposits at Qizong hydropower station is similar to other engineering in west China, and there are some advantages that the dry density of the coarse-grained soil is larger, and the bearing capacity is greater. As a result, the engineering characteristics of the deposits at Qizong hydropower station meet the geological conditions of high rockfill dam construction.(6)The result of stability analysis of the deposit at the dam site indicated that, 1) sliding of the dam foundation is in low possibility because deep and thick deposits are mainly composed of boulder and gravel stratum with compact structure and high strength; 2) the stratum of③-1 and①might generate failure by piping because of their coarse grain and high permeability coefficient; 3) the dam foundation could generate seepage deformation because of quicksand in the③-2 stratum and②-2 stratum with sand soil and silty soil, and the②-1 stratum with fine sand; 4) there are some engineering geological problems, such as non-uniform settlement of the dam foundation, low bearing capacity of dam foundation, and liquification of the dam base, in the③-2 stratum and the②-2 stratum with plenty of lenticle sand seam with variation of thickness and depth of burial.(7)The topographic feature at the dam site is suitable for rockfill dam. Large open style spillway, seepage tunnel, rapid flood passage tunnel, training tunnel and ground factory could be arranged on the cross ridge on the right bank after strengthened supporting. The whole stability of the dam foundation is stable, however, there are some engineering geological problems such as seepage deformation, non-uniform settlement, and liquidation of sand seam in the upper part. Propose was advanced that the lenticle sand seam be excavated in the upper part, the soil of dam base be treated by consolidation grouting and tamping. The deposits’engineering characteristics after treatment can meet the engineering condition of core rockfill dam with 350m height. And as a result, it is suitable for the studied area to construct high core rockfill dam.The research has achieved aims of suitability study for high dam of Qizong hydropower station. And some theoretical and regular achievement are obtained in anisotropy mechanical character of phyllite, origin and engineering character of deep and thick deposits lied under bed river. These achievements can direct excavation of artificial slopes and caverns in the phyllite area, and construction of high dam in the deep and thick deposit.