Hydraulic conductivity and volumetric shrinkage properties review on gradation effect of compacted laterite soil liner

Abstract

This paper reviews the effects of gradation on hydraulic conductivity and volumetric shrinkage properties of compacted laterite soil liner. The distribution of different grain sizes affects the engineering properties of soil such as compressibility, swelling and shrinkage, shear strength, and hydraulic conductivity. It is observed that there are dissimilarities of values in laterite soils from various researches around tropical countries of the world in terms of hydraulic conductivity and volumetric shrinkage. Hydraulic conductivity varies from 4.36×10-3 m/s to 4.7×10-11 m/s and volumetric shrinkage of ≤ 4%relative to fine contents ranging from 1.3% to 69% and coarse contents ranging from 31% to 98.7%.Generally, there is no clear trend established for effects of gradation on hydraulic conductivity and volumetric shrinkage properties of compacted laterite soil liners. This is because laterite soils with less than 50% fines content might not be used as liner or hydraulic barriers because their hydraulic conductivities are less than the minimum requirement of 1 × 10-9 m/s. At times researchers usually left out volumetric shrinkage in their study, but field studies have shown that desiccation can induce severe cracking of unprotected soil barriers. When fine grained soils lose moisture they tend to shrink, which result to cracking that can adversely affect the engineering properties and performance of the soils. The adversative influence includes reduced strength of the cracked soils and increased hydraulic conductivity. It is expected that with logical understanding of the effects of gradation on hydraulic conductivity and volumetric shrinkage properties of compacted laterite soil it will serve as a guide in the design of hydraulic barriers for engineered sanitary landfills in tropical countries around the world.