Abstract:
Expansive soils are active clays soil which its volume changes due to variation in moisture
content that pose problem to civil engineering structures. Therefore the aim of this study is to
improving the strength of subgrade expansive soil using local material or easily available
material of quarry dust and saw dust mixes. The expansive soil sample from Jimma Town around
teknik sefer, with addition of quarry dust alone, saw dust alone, and combination of quarry dust
and saw dust by varying content of stabilizers in steeped concentration of 0%, 10%, 10%, 20%,
20%, 10% + 10% and 20% + 20% each by dry weight of the soil, was used to treat the soil. The
laboratory tests are index tests, strength testes and swelling tests. The preliminary investigation
of the soil shows that it belongs to A-7-5 class of soil. Soil under this class was poor for sub
grade construction. The quarry dust and saw dust addition to expansive soil subgrade soil
improves plasticity index and reduce plastic deformations. The soil bearing ratio (CBR)
continuously increases from 1.36 to 5.6% with quarry dust and saw dust dosages of 0-20%. And
20% quarry dust and 20% saw dust selected as optimum additive to improve and make the
Jimma Town expansive soil suitable for subgrade soil stabilization. The liquid limit of the
natural soil initially 105% and when in combination with 10% quarry dust decrease to 96% and
at 10% saw dust 98%. When mixing both agents 10% QD + 10% SD and 20% QD + 20% SD
with natural soil was further decreased from 98% to 93%. The plasticity index of the natural soil
continuously decreases from 34% to 29% with addition of 20% QD + 20% SD. The soaked CBR
values of mechanically modified soil sample blended with 0%, 10%, 10%+10%, 20% and 20% +
20% of quarry dust and saw dust are 1.36%, 1.58%, 1.87%, 1.71%, 2.26% and 4.77% and 5.6%
respectively. Hence, 20% of quarry dust and saw dust was optimum content that makes the
expansive subgrade soil strength stabilized suitable for subgrade construction. The strength of
the natural soil is increase from 1.36 to 5.6 (S1 to S3) and the soil class is also turn from poor to
fair which is applicable for subgrade material. Further investigations of flied study will be
necessary for performance and economic comparative of quarry dust and saw dust with other
agents.
