【作者】 毛海涛；

【导师】 侍克斌；

【作者基本信息】 新疆农业大学 ， 水利水电工程， 2010， 博士

【摘要】 我国地质条件良好的坝址日趋减少,许多可开发的坝址都坐落在无限深透水地基上。而对于建在无限深透水地基上的土石坝,到目前为止还没有提出一套有效的渗流控制计算理论。有学者曾提出:“无限深透水地基按理论计算渗透流量将很大,所以不宜在其上建坝。”但是从现在的实际建设经验来看,在无限深透水地基或较深厚覆盖层上建坝其渗流破坏及渗流量是可防可控的。此外,对于已建在无限深透水地上的土石坝,由于当初设计时仍按有限深坝基的渗流理论进行计算和设计,运行后出现了许多问题,例如:渗漏量过大、渗透破坏严重、坝后地面沼泽化和盐渍化等等,其中部分问题无法用现有的渗流理论给出合理的解释和回答。本论文针对无限深透水地基上土石坝坝基的渗流问题,利用现已被大家广泛认可的数学理论和数值方法来对此进行较深入和系统的研究,并用室内试验对理论结果进行了验证。理论分析包括保角变换、有限元法和边界元法三部分。首先,利用保角变换理论建立了无限深透水坝基渗流计算的数学模型,通过将复杂的地下轮廓转化为平面问题进行研究,推导出一系列的渗流计算公式,利用这些解析公式能很快的计算出坝基渗流的主要参数。该方法属于解析法,优点是计算方法简单、便于掌握;不足之处未考虑坝体渗流问题,且只能适用于均质地基。接着,应用有限元和边界元分别建立了无限深透水坝基渗流计算的数值模型。其中,在有限元模型中,采用一个足够大的半圆渗流区域来模拟无限域渗流边界,并将坝基和坝体进行整体考虑,编写了计算程序,求解出坝体浸润线的位置和大坝的渗流总量;在边界元模型中,利用边界元积分方程来描述稳定渗流的拉普拉斯方程,以此为基础来求解渗流边界上水头和流速,使问题求解。利用VB语言对渗流计算进行编程计算,简化了计算过程,大大提高了计算的效率。有限元和边界元属于数值方法,优点是能较好的拟合实际边界,可以解决复杂边界条件下的渗流问题;不足之处是,计算工作量,不便于掌握。在理论分析的基础上,通过设计砂槽模型试验来验证理论分析的结论。实验中针对坝基采用不同的防渗体来进行数据监测,通过收集大量的实验数据来进行分析研究,与理论数据对比后发现,二者之间能较好的验证,从而说明本文研究的方法较为可靠,计算结果相对准确。通过对无限深透水坝基渗流的综合研究发现,(1)无论采用水平铺盖还是垂直防渗墙,均存在一个有效尺寸,当防渗体达到该尺寸大小后,坝基的渗流量和渗透坡降都会趋于稳定;(2)采用垂直防渗墙时,防渗墙的位置对坝基渗流的影响较大,并求出坝基轮廓的有效渗径;(3)垂直防渗体和水平铺盖在控制渗流效果方面,存在着一定的数量关系,该数值与坝前的水头、坝基的渗透系数以及防渗体的位置等有关,不仅仅是莱茵和布莱认为的3倍关系;(4)通过对坝基下游渗透出逸坡降的计算,可以较准确的确定出坝后反滤层的铺设范围。此外针对无限深透水坝基下游出现的土壤次生盐渍化问题,提出了“生态长度”概念,并推导出计算公式来求解此长度;对无限深透水地基根据地质情况不同进行了分类,并针对不同的地质情况提出了适合于此类坝基的防渗措施等。最后,在文章中结合了大量的工程实例来进行计算,使理论、实验和实际工程得到了较好的验证,找出无限深透水地基上土石坝坝基渗流的基本规律。更多还原

【Abstract】 The dam locations with the good geologic condition gradually are decreasing in our country, many dams which will be developed have to be seated on the infinite deep foundation. But there is not a suit of seepage control calculation theoretic effectively by far. The paper aims at the seepage calculation of the infinite deep pervious foundation to do a deeply and systemic analysis using the numeric calculation approbatory method and mathematics method, finally to validate by the experimentation.The theoretic analysis part of the paper is that author uses the conformal transformation to establish a mathematics model of infinite deep pervious foundation, the model makes the complex subterranean contour to transform a plane and to study and ratiocinates a series of seepage calculation formulas. According to the characteristic of foundation soil, we can confirm the scope of filtrate layer. The numerical method part of the paper includes FEM and BEM. First, author uses the FEM establish a model of infinite deep pervious foundation; we can get the seepage discharge, seepage gradient and location of paretic line. Besides, author uses the BEM to establish models of horizontal blanket and vertical cut-off wall respectively and to calculate. Based on the theoretic analysis and numerical method, author uses seepage sand groove experiment to validate the above conclusions by collecting the dates when the foundation took the different anti-seepage. At the same time, this paper build a model of“preventing of the up and drainage the down”, find out the relations of anti-seepage measures and ground water level of the downstream, seek after a right size of anti-seepage measures to prevent the solid sanitization of downstream.Based on the validating of each method, to calculate the actual project and find that the horizontal blanket has a effective length, the size is 22-30 times than water-head of upstream; the vertical cut-off wall exist a effective depth is 11-15times than water-head of upstream, when the size of anti-seepage measures reaches to the effective scope, we prolong the size of anti-seepage measures is not significance. Through studying the anti-seepage effect of the both measures, we find that there is a given relation between them, the anti-seepage effect of vertical cut-off wall is 1.5-3.5 times than horizontal blanket’s. Besides that author find that it will affect the seepage discharge and average seepage gradient of dam foundation when the position of vertical cut-off wall is changed under the dam foundation, the best position should be located the forefront of dam base and the worst position is located the middle of dam base.The scope of filtrate layer is count for much with the pervious or not of dam. When the dam is impervious, the worst point of seepage escape gradient is located on the corner of downstream dam slope, the number goes to infinity, so we can letdown the seepage escape gradient of the corner. The filtrate layer should be set from the point. When the dam is pervious, the worst point is the joint of vertical cut-off wall and dam base, the number is H/πs (H is the water-head of upstream, s is the depth of cut-off wall). The filtrate layer should be set from the joint.On the premise confirm of the horizontal blanket effective length, author bring forward the calculation method of economical length about horizontal blanket. Through actual project analyzing, we find that the economical length is longer much than the length of common horizontal blanket which is on the limited deep pervious foundation (6-8 times water-head of upstream). It shows that the length of horizontal blanket is not economy but also is not in reason. Aims at the soil sanitization problem of actual engineering (plain reservoir based on the infinite deep pervious foundation), author brings forward the concept of ecotypes length of horizontal blanket, and constitutes a integrality calculation formulas when the downstream located a drainage well.Finally, according to difference of the geology, author takes the infinite deep pervious to divide into three types: monolayer configuration, double deck configuration and complex configuration. Integrative analyze from anti-seepage effect, project cost, construction, etc, suggests that the best anti-seepage measures is horizontal blanket when the foundation is belong to the monolayer configuration or double deck configuration, but to the complex configuration, the choice of anti-seepage should be all-round, whether takes vertical cut-off wall or not, we should pay attention to the distributing and place of weak pervious layer.更多还原