Abstract:
Expansive soils are difficult to use as construction material for highways, airfields and
lightweight structures. Expansive soils are susceptible to considerable volume changes
due to seasonal variations and moisture content; light weight structures cannot exert the
necessary counter load to overcome the swelling from expansive soil. The availability of
expansive soil along the alignment of road projects has a significant influence on planning,
design, construction, and maintenance of the road. Therefore, the aim of this study is to
evaluate and compare the improvement in engineering properties of expansive soil modified
with stone dust and brick dust as a sub-grade soil. Several methods have been developed for
successful improvement of expansive Soils. For this study two sub grade soils were collected
from Jimma Town around Shanen Gibe (jimma bus station) and around Merkato. A Soil
samples were collected from depth of below 1.5m. Laboratory tests were conducted to
determine moisture content, free swell test, grain size analysis, specific gravity, Hydrometer
test, Atterberg limits, compaction test, California Bearing Ratio and CBR swell tests.
Depending on the tests conducted in the laboratory the optimum percentage of stone dust and
brick dust obtained were at 20% and 40% respectively. The laboratory test result confirmed
that, modification of expansive soil with stone dust and brick dust improves its engineering
properties of expansive soil. From the analysis results, the CBR value is increases from the
1.78% to 21.7% by using stone dust and from 1.78% to 8.75% by using brick dust at the
optimum percentage. Addition of both stone dust and brick dust increases the plastic limit
and decreases the liquid limit and plasticity index of the expansive soil sample. Generally, as
the addition of both stone dust and brick dust ratio increased the FS, LL, PL, OMC, CBR
swell decreased and inversely the PL, MDD are increased and recommended that
modification of expansive soil with stone dust can be used to increase the strength capacity
of foundation and subgrade. In addition both the stone dust and brick dust can be gained
with low cost, locally available and finally makes the environment to become safe.
