Problematic Sub-Grade Soil Reinforcement Using Local Natural Fibers on Selected Road Section From Wolaita, South Western Ethiopia
No Thumbnail Available
Date
2018-05-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
A road is very important for the community, because it is base for the socio-economic interaction
among people. Based on road life and its economic considerations, road pavement designs
mainly need good sub-grade materials or reinforcement of existing problematic soil. Natural
fibers have capability to reinforce problematic soils such ranging from clay to silty sand.
Wolaita (project area) is one of the highly populated area in Ethiopia and its land is almost
completely covered by farm and house. The soil in wolaita area is lateritic clay. However, road
construction site’s soil does not fulfill the sub-grade soil requirements economically. Hence
hundreds of millions metric cube soil is needed for sub-grade layer and the same volume of soil
is cut to drop site in one road project. This research work come up with mechanism, mechanical
conjugation of random distributed local natural fibers and soil, in order to reinforce the
problematic sub-grade soil.
In general the research work comprises the tasks such as characterization and selection of
fibers, representative problematic soils and soil-fiber mixtures. Method of characterization is
done as per AASHTO and ASTM test methods which are recommended in Ethiopian Road
Authority. Accordingly the characterization of the worst problematic soil and selected fibers
(Enset ventricosum and Teff straw fibers) is done before conjugating them. The effect of fibers
percentage by weight and of fiber length in the soil on CBR, surcharged swell, dry density,
moisture content and their optimum improvements are discussed in this paper. The percentage of
individual fiber in the soil is taken as 0%, 0.25%, 0.5%, 0.75%, 1%, and 1.25% by air dry
weight. The result show that MDD is decreased and OMC is increased with increased fibers
percent while CBR value is increased until 1% for Enset fiber and 0.75% for Teff straw fiber
with fiber length of 6 cm. However, the degree of improvement of fiber mixed soil is 157 and 133
times greater than the soil without the fiber respectively. One point unsoaked CBR test shows
that the value increased from 57% to 62%. 4.54kg surcharged swell value of teff straw fiber
conjugated soil is decreased from 5 to 3 as percent of fiber increased from 0% to 0.75%,
respectively and decreased from 5 to 3.5 as fiber increased from 0% to 1% respectively for Enset
fiber. According to improvement, change in road pavement design as per ERA manual and its
subsequent benefits are also discussed in this paper. Finally, appropriate recommendations are
written according to the finding.
Description
Keywords
Reinforce, Problematic Soil, CBR, Natural Fibers, Enset Fiber, Teff Straw, Sub-Grade