Stabilization of expansive soils from Enugu Shale, in Enugu Area Southeastern Nigeria with lime, cement and coal fly ash admixtures were investigated with the aim of improving the engineering behavior of expansive soils. Samples of expansive soils were treated with lime, cement and coal fly ash admixtures. Lime and cement are chemical additives while coal fly ash is a pozzolan .Engineering performance of treated soils were evaluated using Atterberg limits, California bearing ratio and Maximum dry Density .The Atterberg limits of untreated soil were 42.0%, 22.55% and 4.3% for Liquid limit, Plasticity index and Linear shrinkage . The California bearing ratio of untreated soil was 2.3% and 1.1% for usoaked and soaked expansive soils. The Maximum Dry Density of untreated soil was 1.32 Mg/m3 .According to the Casagrande’s plasticity chart, the soil plots as inorganic clay of medium plasticity which necessitated the need for chemical treatment. The stabilization result showed reduction percentages of 29.76% % (42.0 to 29.5), 56.67% (42.0 to 18.20) for cement, cement-coal fly ash mixes on liquid limit. Also a maximum reduction of 21.43% (42.0 to 33.0), 30.95% (42.0 to 31.2 %) on liquid limit for lime lime-coal fly ash mixes respectively. A higher reduction percentage on plasticity index for cement, cement-coal fly ash mixes and lime and lime-coal fly ash were established as 90.67 % (22.5 to 2.10 ), 96 % (22.5.5 to 0.90) and 54.67%(22.5 to 10.2),71.56%(22.5 to 6.4) . A remarkable increase in California bearing ratio value of approximately 400 to 500% ,300 to 700% and 300 to 700, 350 to 900% increase in strength gain for lime, lime-coal fly ash and cement, cement-coal fly ash mixes respectively for unsoaked soil samples. Also a strength gain of 100 to 180%, 100 to 200% and 100 to 200%, 100 to 300% was achieved for Lime, Lime-Coal Fly ash and ce ment, ce ment coal fly ash samples respectively for soaked samples..The Maximum Dry Density showed the highest percentage increase of 543.95%(1.32 to 8.50 Mg/M3 ) and 875.76%(1.32 to 12.88 Mg/M3 ) for cement and cement-coal fly ash mixes, and an increase of 415.15%(1.32 to 6.8 Mg/M3 ) and 642.42%(1.32-9.8 Mg/M3 ). Treatment of the soil resulted in increased strength and reduced swelling potential, however, portland cement provided highly effective clay stabilization, usually with the added benefit of higher strength gain when combined with CFA.

Keywords : Expansive soil, Cement, Lime, Coal Fly ash, Stabilization CBR, Atterberg limits, Pozzolan