垫层是面板堆石坝的重要分区之一。青海石头峡水电站面板堆石坝填筑施工之前,河床砂砾石料场的检测成果显示,筛除100 mm以上直径颗粒后的土料(直接筛分料),其细颗粒含量很容易低于要求的垫层料范围下限。针对直接筛分料和过渡料开展了渗透变形和反滤试验,运用数值模拟方法预测了大坝渗流场分布及垫层与过渡区可能出现的最大渗透比降。从大坝渗漏控制和渗透稳定性功能要求出发,分析认为直接筛分料不适用于石头峡大坝垫层。针对直接筛分料提出了改进方案,即掺入粒径5 mm以下的颗粒,通过渗透变形和反滤试验复核了改进料作为垫层料的适用性。工程建成后,水库蓄水期间运行性态良好,并经受了地震的考验。通过实例研究,强调了填料特性研究应贯穿土石坝建设的全过程,尤其应重视填筑施工之前尽早开展实际用料适用性的复核试验与评价工作。

Cushion layer is an important subarea of concrete faced rockfill dam (CFRD). Prior to the construction of CFRD for Shitouxia Hydropower Station in Qinghai, China, sandy gravel materials collected from riverbed were checked, and the results revealed that the weight percentage of fine grains in the samples screened under mesh size of 100 mm( directly screened cushion material) was likely inferior to the low limit required for cushion layer. Seepage destruction and filter tests were performed for the directly screened materials and transition zone materials. Seepage field in the dam and probable maximum hydraulic gradient values both in cushion and transition zones were forecasted by numerical simulation method. The applicability of tested samples were assessed on the basis of seepage characteristics for cushion zone materials in response to the functional requirements of water leakage and seepage destruction control. The directly screened materials were judged unsuitable for cushion layer. Moreover, a scheme was proposed to improve the filling material by adding fine grains screened under mesh size of 5 mm to the directly screened material. The improved materials were checked with seepage destruction and filter tests, and were demonstrated applicable for dam cushion layer. The dam has been built up and has performed well during reservoir impoundment even under earthquake. This example tells the necessity of research on filling material throughout the construction of any embankment dam. Proof tests and applicability assessment should be taken for the natural or produced materials as early as possible before the dam fill construction.