Stabilizing Expansive Subgrade Soil on a Selected Road Section in Eastern Part of Ethiopia in Somalia Region Jigjiga Tuli
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Date
2021-09-18
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Addis Ababa University
Abstract
The long-term performance of any construction project depends on the soundness of the
underlying soils. Unstable soils can create significant problems for pavements or structures.
In order to avoid most of the problems that has been appearing on the upper layer of any
pavement it is better to treat the subgrade soil. To achieve the research objectives, subgrade
soils samples were collected along the corridor of the road section and evaluated for their
physical and geotechnical properties. The laboratory results of previous investigations on the
area show that approximately 71 percent of the existing soil has a plastic index (PI) ranging
from 27 to 35 percent and a liquid limit (LL) ranging from 55 to 70 percent with an average of
62.5 percent and <5% California bearing ratio (CBR) and approximately 89 percent of the
swell values are greater than 2%. This reveals that the sub-grade soil along the route project
is primarily characterized by A-7-5 and A-7-6 according to the American Association of State
Highway and Transportation Officials (AASHTO) and fat clay (CH) and elastic silt (MH) of
UCS soil classification which is considered as a problematic soil for subgrade materials. The
swelling pressure of natural subgrade soil was determined using the laboratory to evaluate the
fill height of the embankment on the geotechnical properties of soil. Because the swelling
pressure of the sub-grade material has a medium swell potential and low potential heave, so
soil replacement of only shallow soil not exceeding 30 cm is sufficient (only for the selected
stretches) to equalize the swelling pressure of the existing soil with lower swelling potential,
higher workability, and stabilized soils were feasible to be used as subgrade materials.
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Keywords
Stabilizing Expansive Subgrade Soil, Selected Road Section, Eastern Part, Ethiopia, Somalia, Region Jigjiga-Tuli