Hydraulic anisotropy of unsaturated soils with unimodal and bimodal characteristics

Abstract

Hydraulic anisotropy of a soil represents a directional dependence of its permeability. Past research on hydraulic anisotropy under unsaturated condition were mainly limited to the extent of theoretical concept. The available experimental results in literature focused only on one particular soil mixture, i.e. 50% sand and 50% kaolin. This project advanced the experimental study of those literatures. It aimed to understand the hydraulic anisotropy characteristics of unsaturated soils with unimodal and bimodal characteristics and to examine its relationship with fines content. Laboratory experiments comprising index soil properties, soil-water characteristic curve (SWCC), and saturated and unsaturated permeability tests of compacted soil made of 30% sand and 70% kaolin were carried out. Experimental results indicated that at a given composition, soil with unimodal SWCC (compacted at wet of optimum) has a higher hydraulic anisotropy as compared to soil with bimodal SWCC (compacted at dry of optimum). Hydraulic anisotropy of soil became less prominent with the increase in fines content and the decrease in dry density. Furthermore, hydraulic anisotropy in the unsaturated condition exhibited similar values to that in the saturated condition, regardless of its initial compaction conditions. In addition, evaluation towards statistical model to estimate unsaturated permeability substantiated the applicability of the estimation to indirectly determine hydraulic anisotropy of soil with unimodal and bimodal SWCCs.