1、简介：评估抗滑混凝土重力坝的安全要求的理解是，岩基和他们上面的结构是一个互动的系统，其行为是通过具体的材料和岩石基础的力学性能和液压控制。大约一个世纪前，Boozy大坝的失败提示工程师开始考虑由内部产生渗漏大坝坝基系统的扬压力的影响，并探讨如何尽量减少其影响。今天，随着现代计算资源和更多的先例，确定沿断面孔隙压力分布，以及评估相关的压力和评估安全系数仍然是最具挑战性的。我们认为，观察和监测以及映射对大型水坝的行为和充分的仪表可以是我们更好地理解在混凝土重力坝基础上的缝张开度，裂纹扩展，和孔隙压力的发展。图.1流体力学行为：（一）机械;（二）液压。本文介绍了在过去20个来自Albigna大坝，瑞
2、士，多年收集的水库运行周期行为的代表的监测数据，描述了一系列的数值分析结果及评估了其基础流体力学行为。比较了数值模拟和实际行为在实地的监测结果。在此基础上比较了一系列的结论得出了基本孔隙压力在节理岩体的影响可以考虑在其他工程项目，认为那里的岩石节理流体力学行为应予以考虑。这些项目包括压力管道，危险废物处置，以及对流动行为的控制断面沿岩石地质遏制依赖的其他情形。流体力学的行为自然对先进设备，机械和个别岩石节理的水力特性的概要。一个对岩石联合流体力学行为的更详细的描述中可以在阿尔瓦雷斯（1997年）和阿尔瓦雷斯（1995年）和在实验室调查和数值模拟模型进行了乌鸦和Gale（1985），Gentie
3、r（1987年），江崎等人（1992），和其他人中发现。该水力行为的联合可以表示为非线性应用之间的有效正应力双曲线关系，,并联合， 在装卸，重大的联合封发生在低有效正应力的地方。该单位的压力关闭规模迅速下降，但是，随着应力水平增加。双曲线的定义是由初始切线刚度定义，并联合最大的渐近结束，。这种关系也是非线性，迟滞的卸载条件，直到成为有效正应力为零（图1a）。和的价值观通过对实验数据的回归分析来估计的。对于自然和花岗岩裂隙，这些参数都是相互关联的下列限制范围之间的阿尔瓦雷斯等。 （1995年）：这里的单位是M pa/m， 的单位是m粗糙关节展览最大规模的联合最高和最低的封闭初始关节僵硬，关节光滑
4、而有最低和最大的岩石的共同特点是液压行为之间的线性关系液压孔径，它控制流动规模，关闭和机械联合，用于水平应力。液压孔绘制相应的联合与关闭（图1b），以获取拦截线，起始水力孔径，边坡系数和耦合，而“刻画了联合流体力学行为，i. e，两者在液压机械孔径由于孔径的变化变化的关系，鉴于其中是剩余的水力孔径对于给定的岩石节理，两者之间是有粗糙度及耦合系数的关系，因为f的分布和沿关节面流道曲折而定。对于理想的平行板，以在整个关节面单流道，f= 1.0.对于集中流道蜿蜒穿过关节面，f1.0。因此，用经典的立方定律表示通过岩石节理流率：其中Q是流量;是水的单位重量;是沿岩石节理头部下降;是水（11.005ps
5、）的动力粘度;是联合液压孔径而G是形状因子，由水流几何而定。直流地下G=W/L（其中W和L是宽度和长度，分别联合），为不同径向流，G =2/ln（re/）,其中和re分别为内外圆柱面半径。裂隙岩体渗透性随深度变化另外，岩体等效渗透，公里，可以以同样的形式作为修改后的定律，或在液压口径计算，同样的形式占关节间距，S:在裂隙岩体渗透性的变化，由于覆盖层和围应力，计算。 1 - 3。岩体的渗透性，K，理论的深度关系的结果高达1000米，采用当量。 5载于图2。孔的液压随覆盖减少强调在岩体渗透性，随深度的增加，从 cm/s到附近的水面在600厘米深度/秒 - 1000米的结果估计岩体渗透性得到假设f=
6、 1.0，= 10，这是在实验室测试中取得的值与（阿尔瓦雷斯等al.1995）相似，巴西在这一测试中描述位置的花岗岩编队部分。覆盖层讲估计使用的是26.0 kN/m3单位重量。在这种情况下，它的假设是横向和纵向应力大致相同（土压力系数Ko = 1.0），这也被认为将在巴西的测试位置的火成岩地层的代表，但其他价值在原位强调可以预计，如对高e.g., for Ko1.0，垂直节理将有较大的渗透率。在深露天矿在巴西花岗岩开采项目获得的场渗透率测量在图2中绘制与理论的关系比较。联合间距从钻孔岩心观察值都在数米范围内，从而产生了一个5米间距是常数的计算假设。阿霍的价值在300 -1000m范围被用来确定
7、公里= f的理论关系（z）的，其中Z是深度，以实地测量和比较这两个钻孔测量值相对渗透率在100至200米深处的高，可能表明的一个区或剪切节理岩带更多的存在。所测岩石渗透率稳步下降，在深度的增加，然而，它们的值与对应的岩体渗透性的理论与模型估计趋势良好。典型液压孔径400 -500m的和后关节僵硬= 10V的双曲线关系，与三菱商事和= 似乎同意这些结晶岩体观测场行为良好。图.2.裂隙岩体渗透性随深度的关系。虽然真正的流体力学节理岩体的行为是需要考虑具体的地点和地质因素，该方法提供了一个框架，但在设计阶段，其中岩石资料尚未提供大规模渗透。Hydromechanical analysis of fl
8、ow behavior in concrete gravity dam foundationsAbstract: A key requirement in the evaluation of sliding stability of new and existing concrete gravity dams is the prediction of the distribution of pore pressure and shear strength in foundation joints and discontinuities. This paper presents a method
9、ology for evaluating the hydromechanical behavior of concrete gravity dams founded on jointed rock. The methodology consisted of creating a database of observed dam behavior throughout typical cycles of reservoir filling and simulating this behavior with a distinct element method （DEM） numerical mod
10、el. Once the model is validated, variations of key parameters including litho logy, in situ stress, joint geometry, and joint characteristics can be incorporated in the analysis. A site-specific simulation of a typical reservoir cycle was carried out for Albigna Dam, Switzer land, founded on graniti
11、c rock, to assess the nature of the flow regime in the rock foundations and to evaluate the potential for sliding surfaces other than the damrock interface to develop. The factor of safety against sliding of various rock wedges of differing geometry present within the dam foundations was also evalua
12、ted using the DEM model and conventional analytical procedures. Estimates of crack propagation patterns and corresponding uplift pressures and factors of safety against sliding along the damrock interface obtained with the DEM were also compared with those from simplified procedures currently used i
13、n engineering practice. It was found that in a jointed rock, foundation uplift estimates after crack development obtained from present design guidelines can be too conservative and result in factors of safety that are too low and do not correspond to the observed behavior. Key words: Hydromechanical
14、, jointed rock, flow, dam design.Introduction: Evaluating the safety of concrete gravity dams against sliding requires an understanding that rock foundations and the structure above them are an interactive system whose behavior is controlled by the mechanical and hydraulic properties of concrete mat
15、erials and rock foundations. About a century ago, the failure of Boozy Dam prompted dam engineers to start considering the effect of uplift pressures generated by seepage within the damfoundation system and to explore ways to minimize its effect. Today, with modern computational resources and much m
16、ore precedent, it is still most challenging to determine the pore-pressure distribution along foundation discontinuities to assess pertinent stresses and evaluate factors of safety. It is our opinion that observing and monitoring the behavior of large dams on well mapped and adequately instrumented
17、foundations can bring important insights for a better understanding of factors controlling joint opening, crack propagation, and pore-pressure development in foundations of concrete gravity dams.Fig.1.Hydromechanical behavior of natural joints :（a） mechanical;（b）hydraulic.This paper presents behavio
18、r representative of cycles of reservoir operation in the last 20 years collected from monitored data of Albigna Dam, Switzerland, and also describes the results of a series of numerical analyses carried out to assess the hydromechanical behavior of its foundations. Comparisons are made between resul
19、ts of numerical modeling and the actual behavior monitored in the field. Based on these comparisons, a series of conclusions are drawn regarding basic pore-pressure buildup mechanisms in jointed rock masses with implications that may be considered in other engineering projects, where the hydromechan
20、ical behavior of jointed rock should be considered. Such projects include pressure tunnels, hazardous waste disposal, and other situations dependent on geologic containment controlled by flow behavior along rock discontinuities.Hydromechanical behavior of natural joints A brief summary of the state-
21、of-the-art of mechanical and hydraulic behavior of individual rock joints is presented here. A more detailed description of rock joint Hydromechanical behavior can be found in Alvarez（1997）and Alvarez et al.（1995）and in investigations in laboratory and numerical model simulations carried out by Rave
22、n and Gale （1985）, Gentier （1987）,Esaki et al.（1992）,and others.The mechanical behavior of the joint can be represented by a nonlinear hyperbolic relationship between the applied effective normal stress,， and joint closure, During loading, significant joint closure takes place at low effective norma
23、l stresses. The magnitude of the closure per unit of stress decreases rapidly, however, as the stress level increases. The hyperbola is defined by the initial tangent stiffness, and the asymptote maximum joint closure, . This relationship is also nonlinear and hysteretic for the unloading condition
24、until effective normal stresses become zero （Fig.1a）.The values of and are estimated by regression analysis on experimental data. For natural and induced fractures in granite, these parameters are interrelated and range between the following limits Alvarez et al. （1995）:Where is in M pa/m and is in
25、Rough joints exhibit the largest joint maximum closure and the lowest initial joint stiffness, whereas smooth joints have the lowest and the largest The hydraulic behavior of the rock joint is characterized by the linear relationship between hydraulic aperture, which controls the magnitude of flow,
26、and mechanical joint closure, , which depends on stress levels. Hydraulic apertures are plotted versus their corresponding joint closure （Fig.1b）to obtain the line intercept, ,initial hydraulic aperture, and the coupled slope coefficient, ,which characterizes the hydromechanical behavior of the join
27、t ,i. e., the relationship between changes in hydraulic aperture due to changes in mechanical aperture, given byWhere is the residual hydraulic aperture.For a given rock joint, there is a relationship between roughness and the coupled coefficient, because f depends on the distribution and tortuosity
28、 of flow channels along the joint surface. For ideal parallel plates, with a single flow channel along the entire joint surface, f=1.0.For concentrated flow channels meandering across the joint surface, f1.0.Hence, the classic cubic law expresses flow rate through a rock joint:Where Q is the flow ra
29、te;is the unit weight of the water;is the head drop along the rock joint; is the dynamic viscosity of the water（1.005Pas ）; Is the joint hydraulic aperture; and G is the shape factor, which depends on the geometry of flow. For straight flow, G=W/L （where W and L are the width and length, respectivel
30、y, of the joint）; and for divergent radial flow, G=2/ln （re/）, where and re are the borehole and external cylindrical surface radiuses, respectively.Jointed rock mass permeability change with depthAlternatively, the rock mass equivalent permeability, km, can be expressed in the same form as the modified cubic law, or in terms of hydraulic aperture, to account for spacing of the joints, S:Changes in jointed rock mass permeability due to overburden and confining stresses were calculated using eqs. 1 3.The results of a th
