Thoughts on gradation design of filter materials
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摘要: 反滤料的级配设计是土石坝设计的核心问题之一。反滤料设计除了要满足规范中滤土、排水、保护被保护土裂后自愈的要求外,还应能适应较大剪切变形,起到变形过渡的作用。 将土料分为“骨架粗料”和“填充细料”两部分,并用此模糊概念,将《碾压式土石坝设计规范》的 反滤料 设计观念具体化:①探讨了含有大于 5 mm 颗粒的防渗混合土的宏观概念,指出其细粒组含量 η 0.075 与大于 5 mm 颗粒的含量 P 5 是一对“因土而异”的特征值,可沿用美国垦务局的反滤准则中对被保护基土的四个分类及各类的反滤关系,但得到的反滤料的 D 15 应视为反滤料“填充细料”的 D 15 ;②从刘杰对渗透变形的分类研究中,可引伸出 反滤料的 “骨架粗料”和“填充细料” 的 分界粒径 d f 和“填充细料”的临界含量 η f ,并将反滤料的设计依据归结为九项条件;③通过实例,详细地解说了反滤料的实用设计方法。Abstract: The gradation design of filter materials is one of the key problems in design of earth rockfill dams. The design of the filter materials, besides meeting the standard requirements of soil filtering, water drainage and protecting the protected soil by self-healing after cracking, should adapt to large shear deformation and make the effect of deformation transition. The soil materials are divided into two parts, coarse skeleton materials and fine filling materials. Based on this fuzzy concept, the design idea of the filter materials in the design code for rolled earth-rock fill dams (SDJ218-84) in China is specified as follows: (1) The macroscopic concept of mixed impervious soil containing particles which exceed 5 mm in diameter is discussed. The content η0.075 for fine particles and the content P5 for particles exceeding 5 mm in diameter are a pair of eigenvalues and different for different soils. The four classifications of protected soils and their filter relationship in each classification in the filter criterion of US Bureau of Reclamation can still be used, but the particle size D15 should be that of the fine filling materials in filter soil instead; (2) From the classification of leakage deformation in Liujie’s study, the demarcation particle size d f between the coarse skeleton materials and the fine filling materials, and the critical content η f for the fine filling materials are proposed. Furthermore, the design basis of filter materials is summarized to be nine conditions; (3) through an example, the practical design method for the filter materials is introduced.
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