The performance of roads depends mainly on the strength of the underlying subgrade soil. Blackrncotton soil gives rise to the failure of the road constructed on it. These soils have cyclic volumernchange due to fluctuation of moisture content. The degree of volume change or expansivenessrndepends on the mineralogical composition of the soil. Black cotton soil with montmorillonite is arndominating mineral and experiences high volume changes cause considerable failure to thernstructures constructed on it.rnThe current study was conducted on modjo â€“edjere road project where subgrade soil is black clayrnsoil. The road failed with in liability period showing longitudinal cracks on carriage way andrnshoulder of the road. This thesis was conducted to evaluate the adequacy of the replacement depthrnand replacement materials type made for the road. Accordingly, both disturbed and undisturbedrnsoil samples were brought from the site for laboratory tests both for subgrade soil andrnreplacement materials.rnHence, swelling pressure and bulk density of the soil were determined from undisturbed subgradernsoil samples. Cracked sections of the road stretch were selected and excavation was made tornknow the origin of the cracks. Hence, cracks were originated from subgrade soil and depths ofrncracks were measured for the selected sections of the road from natural ground level.rnReplacement depth was determined from measured swelling pressure and compared to the crackrndepth actually measured on the field. Accordingly, replacement depth of 60cm which was madernfor the road under study is insufficient to counter balance upward swelling pressure from nativernsubgrade soil. Moreover, It was also seen that overburden pressure of the pavement structure isrnless than measured swelling pressures.rnKey Words: Road performance, Black Cotton Soil, Swelling Pressure, Replacement Depth,rnReplacement Materials Types