泥石流拦砂坝通常建造在沟床堆积物上。泥石流堆积物的渗透性是影响坝底扬压力的关键因素。目前关于土体渗透性的研究主要集中于无黏性粗粒土，对泥石流堆积物这种宽级配土体渗透性的研究比较缺乏。选择北川县泥石流沟床堆积物作为试验材料，通过渗透试验，确定了影响宽级配土渗透性的细颗粒上限粒径；在此基础上，通过试验研究了细颗粒含量与渗透系数的关系。结果表明，泥石流堆积物中粗颗粒仅起骨架作用，细颗粒才是决定其渗透性能的关键；显著影响宽级配土渗透性的细颗粒上限粒径为0.1 mm；细颗粒（<0.1 mm）含量与渗透系数呈负指数关系，并且当细颗粒含量超过20%以后，泥石流堆积土的渗透性趋于稳定。

The permeability of debris flow deposit, if served as a foundation of check dam, is vital to forming uplift pressure on dam base. Current researches on soil permeability are focused on cohesionless coarse-grained soils and few on wide graded gravelly soils, such as debris flow deposits. The upper limit particle size of the fine particle affecting the permeability of wide graded gravelly soil is determined by the permeability test on the debris flow deposit in Beichuan county, Sichuan Province of China. The relationships between fine-grained soil content and permeability coefficient are also obtained. The results show the coarse particles only play a skeleton role, and the fine particles dominate the permeability of debris flow deposits. The upper limit particle size of 0.1 mm has significant influence on the permeability of wide graded gravelly soil. The content of fine particles (<0.1 mm) has a negative exponential relationship with the permeability coefficient, and the permeability of debris flow deposits tends to be stable when the fine particle content is more than 20%.