基于颗粒级配参数描述砂土持水及非饱和强度特性的土壤转换函数

以van Genuchten模型为基础,将砂土的基本物理特征与统计分析相结合,构建土壤转换函数以预测砂土持水曲线。首先,在土壤转换函数中引入控制粒径d_(60)和不均匀系数C_u这两个典型颗粒级配参数,并满足完全均匀和完全分散的两种理想颗粒材料条件;其次,结合非饱和土水力特性数据库(UNSODA)与4种颗粒级配分布较均匀的砂土持水曲线补充试验,通过量纲分析和回归分析,将控制持水曲线进气值和减湿率的参数a和n分别表示为d_(60)和lgC_u的反比例型转换函数,结果表明:这两种转换函数对参数a和n的预测效果优于已有转换函数;最后,将这两种转换函数引入非饱和强度公式,利用已有文献中的非饱和强度试验结果验证了提出的土壤转换函数在表征砂土毛细黏聚力与抗拉强度随基质吸力变化规律的有效性,相应的理论计算结果表明:砂土的毛细黏聚力随其控制粒径减小或均匀程度降低而增高。

Pedotransfer functions to describe water retention and unsaturated strength behaviors of sandy soils based on particle size parameters

Based on the van Genuchten model,two pedotransfer functions are proposed to predict the water retention curves of sandy soils. Particle size parameters of the controlling particle size d₆₀ and the coefficient of uniformity Cu are employed in the pedotransfer functions with two idealized conditions,i.e.,the extremely monosized and polydisperse conditions. Water retention tests are carried out on four sandy soils with narrow particle size distributions as supplementary data of the UNSODA database. Based on the dimension and regression analysis,the parameter a and n,which are related to air entry value and drying rate of water retention curve,are expressed as inversely proportional to d₆₀ and lgC_u. The proposed pedotransfer functions have better fitness than previous functions for sandy soils. The proposed pedotransfer functions are finally imbedded in unsaturated strength equations, which provide a way to predict the evolution of capillary cohesion and tensile strength with matric suction. The prediction shows quantitative agreement with experimental data in the previous literatures,and the theoretical solutions indicate that the capillary cohesion is generally higher for materials with finer controlling particle size or lower uniformity.