Stabilization of Expansive subgrade soil using Lime and Sorghum husk ash mixed with lime for pavement construction

Abstract

Expansive soils have considerable volume changes, which related to the change in its moisture content. The sudden change of the volume in the expansive soil can cause major damages to the overlying structures such as highway pavements. Stabilization is one of the methods by which the engineering properties of expansive soil can be improved. The main objective of this research is to evaluate the feasibility using of sorghum husk ash with lime as a stabilizer of an expansive subgrade soil material. A series of laboratory experiment has been conducted on 0, 2, 4, 6 and 8% lime and a mixture of both by keeping 5% lime constant and varying sorghum husk ash content to 3, 5, 7 and 9% by dry weight of the soil. In this study Atterberg Limits Tests, Particle Size Distribution, soil Classification, Free Swell Index, linear Shrinkage, Specific Gravity, Compaction tests, and CBR tests have been determined. The research design was followed the experimental type of study which begins by collecting samples. The sampling technique used for this research was a purposive sampling which is non– probability method. Two expansive soil samples were taken from different borrow pits in Jimma town, the Hermata - Mentina Kebele and Kito Furdisa by observation and free swell index tests at a depth of 1.50 m to remove organic matter. Sorghum husk ash (SHA) was taken from farmer area in Somali region, Ethiopia and Lime was taken from Sankale Lime Factory. Result of the chemical composition of SHA shows that the total content of Silicon Dioxide (SiO2), Aluminum Oxide (Al2O3) and Iron Oxide (Fe2O3) was 77.30% and specific gravity was 2.27. The chemical properties was fulfilling the requirements according to ASTM C-618. The Hermata - Mentina Kebele soil sample has plastic index 56.85%, free swell index 91.70%, linear shrinkage 18.93%, and CBR value 1.17%. Similarly, Kito Furdisa (Bossa-Addis Kebele) soil sample has plastic index 65.99%, free swell index 111%, linear shrinkage 21.07%, and CBR value 0.92%. Since both the given soil samples were found with high degree of expansion, stabilization was made with mix-ratio 2,4,6 and 8% of only lime and a mixture of SHA3% and L5%, SHA5% and L5%, SHA7% and L5%, and SHA9% and L5%. Accordingly, CBR-swell value for both soil samples shows a significant reduction as the ratio of SHA-lime material increase. The CBR-Swell for (Hermata - Mentina Kebele) HMK soil sample reduced by 2.52% (from 3.42% to 0.90%) and that of the (Kito Furdisa) KF soil sample reduced by 3.15% (from 4.26% to 1.11%). This result indicates that blending of SHA-lime material to expansive clay soil minimizes the heaving tendency which occurs due to seasonal moisture variations. Generally, based on the test result performed under this study, the maximum value of CBR for both (Hermata - Mentina Kebele) HMK and (Kito Furdisa) KF soil samples were achieved at 6% lime alone and SHA7% +L5% with CBR value of 8.76% and 8.38%, respectively. And it was the optimum ratio which achieved by most geotechnical parameters of the study. All the laboratory result was compared with standard specifications.