高堆石坝面膜防渗体变形性破坏机理及设计方法

Geomembrane surface barrier of rockfill dam on thick riverbed alluvial deposit has many advantages, such as strong ability to adapt differential deformation, short construction period, low cost, saving land, low carbon and environment protection. However, the deformation failure mechanism of key position of the geomembrane surface barrier has not been systematically revealed. There is still no scientific and reliable basis to refer to when designing the project. In this program, the methods of interface direct tests combined with numerical analysis, structural model tests and environment simulation tests of construction-operation period are employed to investigate the design method and deformation failure mechanism of geomembrane surface barrier for high rockfill dam. Firstly, direct shear tests of PVC geomembrane / contact materials interface is conducted to get the relationship between shearing stress and relative displacement. Then the shearing stress and relative displacement relationship will be incorporated into the three dimensional numerical program, which is then used to analyze the global deformation property of the geomembrane surface barrier of high rockfill dam. Secondly, according to the results of global numerical analysis, structural model tests and material performance tests are employed to investigate to the deformation failure mechanisms of key position and decaying rule of PVC geomembrane performance resulted from complex environment during construction and operation period. Thirdly, the methods of analyzing and calculating the deformation of geomembrane in the key position and evaluating the performance decaying of geomembrane are established on the basis to the experimental results. Finally, the design methods that can avoid the deformation failure of geomembrane surface barrier will be proposed by comprehensive analyzing the numerical and experimental results. The final objective of this program is to provide scientific theory basis for engineering design and construction of high rockfill dam with geomembrane surface barrier.

深覆盖层上高堆石坝面膜防渗体具有能适应差异变形、施工期短、造价低、节约土地及低碳环保等优点。然面膜防渗体关键部位变形性破坏机理尚未揭示，其相关设计计算还无据可依。本课题拟采用界面直剪试验、数值分析、结构模型试验和施工运行环境仿真试验相结合的方法对高堆石坝面膜防渗体变形性破坏机理及设计方法进行系统研究。首先，通过PVC膜与接触材料界面力学特性试验建立界面切应力-切位移关系，并移植到三维数值程序中进行面膜防渗堆石坝整体数值分析；其次，依据整体受力变形特性，按照施工运行期工作性态及环境进行关键部位结构模型和材料性能仿真试验，揭示关键部位破坏机理及施工-运行期复杂环境引起膜变形性能衰变规律；再次，依据试验结果研究面膜防渗体关键部位细小区域变形分析计算方法及膜变形性能衰减评价方法；最后，经综合分析提出面膜防渗体避免变形性破坏的设计方法。本课题旨在为深覆盖层上面膜防渗堆石坝建设提供科学依据和理论基础。

1 摘要.深覆盖层上高堆石坝面膜防渗体能适应差异变形、工期短、造价低、节约土地及低碳环保。国内对堆石坝面膜变形性破坏机理尚未开展系统研究。.（1）面膜锚固部位“夹具效应”及其避免破坏措施的结构模型试验.通过常规面膜铺设锚固与8种改进铺设锚固型式的结构模型试验，揭示了面膜夹具效应的破坏机理；指出惯用设置伸缩节方式是有害的；提出了避免夹具效应的设计思路和方法。.（2）PVC土工膜的在施工-运行期复杂环境下变形性能衰变规律试验.1）环境环境温度对面膜性能的影响。通过对2种PVC膜从-40ºC至60ºC不同环境温度的纵横向拉伸试验，得到弹模与温度关系及其表达式；低温使延伸率降低，柔韧性变弱，实际工程应考量面膜水下4ºC环境的力学性能。2）低温持续大变形对面膜性能的影响。在4ºC环境温度下对2种PVC膜分别进行5%~80%等8种不同初始变形后长达1235h的持续变形试验表明，初始变形量对断裂延伸率衰减影响明显，当初始变形量为80%时，断裂延伸率衰减率高达45.9%； 3）低温持续大角度弯折的面膜性能的影响。2种PVC膜以180 º弯折角度作4ºC环境温度下20~120天持续试验，断裂伸长率最大衰减15.8%；建立了应变能随时间变化的统计模型。.（3）高面膜堆石坝整体结构分析及复杂细小区域的面膜变形数值计算方法.1）由复合膜与垫层间直剪试验建立了以界面剪切劲度系数ks为表达式的双曲线本构模型；2）提出考虑切向位移对面膜顶入垫层孔隙内液胀变形影响的计算方法；3）为模拟锚固部位细小区域发生的夹具效应，将锚固处的膜节点与基岩节点分离开而设置三维弹簧单元；在膜单元和坝体单元间设置连接单元使两种单元间不必一一对应，使整体结构分析中能计算细小区域内的应力应变；自编了可分析细小部位面膜变形的非线性三维有限元计算程序用于工程分析。 .（4）建议面膜周边锚固等特殊部位避免破坏及服役期缩减的设计方法.1）锚固部位防渗膜破坏的设计方法。2）工程设计需提高对面膜垫层平整度的技术要求。