渗透性是砂土的重要工程性质之一，影响砂土渗透性的因素有很多，比如土体密实程度、土颗粒自身特性、流体性质等，其中孔隙率与颗粒粒径是两个重要影响因素。而以往基于混合粒径的天然砂土的研究很难分别对这两个因素进行独立的研究。基于此，首先开展了单一粒径级砂土的常水头渗透试验，分别研究了同一粒径级砂土渗透系数随孔隙率的变化和同一孔隙率下不同粒径级砂土渗透系数随均值粒径的变化规律。试验结果显示，渗透系数随着孔隙率的增加而线性增加、随均值粒径二次方的增加而线性增加，其中均值粒径的影响较大，其变化能导致渗透系数量级上的差异。在此基础上，开展了多粒径混合砂土的渗透试验，讨论了曲率系数、不均匀系数等级配参数对渗透性的影响，从而将单一粒径级的研究成果推广到天然砂土，最终拟合出渗透系数与相关影响因素的经验公式，以便工程实践参考使用。

Permeability is an important property of sand soil. Factors that influence the permeability of sand include density, particle characteristics and properties of the fluid, among which the porosity and particle size are two important ones. However, previous investigations based on natural sand with mixed particles are not able to study the two factors independently. Therefore, constant head permeability tests are firstly carried out on sand soil with single particle size fractions to study the influence of grain size and porosity on the permeability, respectively. For sand soil with the same grain size fraction, the coefficient of permeability is found to increase linearly with the increase in porosity; for sand soil with the same porosity, the coefficient of permeability is found to increase linearly with the increase in porosity the square of average particle size. Based on this, the influence of gradation characteristics on the permeability of multi-particle-size sand soil is studied to extend the results from single particle size fraction to natural sand. The results show that the coefficient of permeability of multi-particle-size sand soil increased linearly with the increase the coefficient of curvature and coefficient of uniformity. The influences of different factors also differ from each other. The change in average particle size leads to change in order of magnitude of the coefficient of permeability. Finally, an empirical equation considering all the above factors is developed for engineering practice.