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The primary step in the construction of sub- base and base course materials is the identification and selection of suitable borrow pits. This is done by obtaining samples from economically feasible borrow pits and testing them in the laboratory. 1 The laboratory compaction with varying compactive effort viz: British Standard (BS) compaction with 2.5kg rammer, repeated on 3 layers of 61 blows each, West African Standard (WAS) compaction with 4.5kg rammer repeated on 5 layers of 25 blows each; and Heavy British Standard (HBS) compaction with 4.5kg rammer repeated on 5 layers of 61 blows each on samples from locations 1 and2 respectively were conducted. Focus was on Unyeghe residualsoils from two distinct borrow-pits stabilized with river sand and ordinaryPortland cement. In all cases, the rammers fell from a height of 450mm above the top of mould. The unsoakedCBRvalues obtained with BS and WAS compactions,34% and 46% respectively,were far below the recommended minimum of 35% and 80% for sub-base and base courses applications by FMW & H 2 (1997) specification.The HBS compaction tends to simulate the actual field condition by limiting the air voids to about 5%. An interesting feature observed is that the highest CBR and MDD values obtained, (132%, 134% and 2100kg/m 3 , 2010kg/m 3 ) occurred at lower moisture contents (7.6%, 9.4%) at both locations. On application of the BS and WAS compactive effort to OPC stabilized Unyeghe residual soil samples the soaked CBRand MDD values at optimal level(124%, 132% and 2000kg/m 3 , 2060kg/m 3 ), showed comparative improvement. This result could not be justified only by direct influence attributable to the stabilizing materials only. It could thus be concluded that both the California Bearing Ratio (CBR) and Maximum Dry Density (MDD) while not being inherent properties of the soil material, are predicated on the applied compactive effort. Hence, the more the soil material is compacted, the greater the value of cohesion and shearing resistance. Multiple nonlinear regressed models were developed for the purpose of prediction and optimization of Unyeghe residual soils with various stabilizing parameters.

Compaction Characterization and Model Prediction of Stabilized UnyegheResidual Soils, AkwaIbomState Nigeria