ABSTRACT
The addition of traces of chemicals in the stabilisation and modification of expansive soils have been a common practice. Basically, lime (hydrated lime and quick lime) have been found to be most effective in reducing the swelling properties of potentially expansive soils. In regions where lime is scarce, cement has been found to be a suitable alternative. In Nigeria, the current prices of cement and lime have been found to be very high, hence the need to look for suitable alternative stabilizers to replace or minimise the use of lime and cement. This thesis considers the effects of local hydrated lime, sand and calcium carbonate on the black cotton soil as compared with those of limbux and cement. From the results of this thesis, it has been found that calcium carbonate greatly improve the workability of the Black Cotton Soils because it reduces the cohesive properties of the soil. For calcium carbonate addition, up to 10% the cohesion of the Black cotton soil can be reduced from 70kN/m3 to 22kN/m3. Although sand can be used to reduce potential expansion of Black Cotton clay, stringent maintenance culture will be required and the cost advantage in using sand depends on the distance through which the sand have vii to be hauled. When sand is used as a stabilizing agent in black cotton soil, 1 to 2% cement is recommended to be added to the soil in order to improve the otherwise low strength and durability properties of the sand stabi1ised soi1. The local lime showed the greatest advantage in terms of cost. It cost about half the price the imported lime and the improvements achieve through it use are high for the calcium oxide content (44.9%) and the percentage of insoluble residue (13.5fc) in it. In other to improve the strength and durability of the lime stabilized soil, it is recommended that a lime/cement combination should be used.