Effect of Soil Suction on the Compressibility and Strength of North-Eastern Nigerian Black Cotton Soil   Oluwapelumi O. Ojuri Department of Civil Engineering, Federal University of Technology, Akure, Ondo State, Nigeria.
			ABSTRACT

The effects of soil suction (negative pore water pressure) on Black Cotton soils, a problematic highway subgrade and foundation soil in North-Eastern Nigeria was examined, by performing stress-strain tests namely triaxial compression and Oedometer test on samples of the compacted partially saturated Black cotton soil, which were also subjected to suction measurements. The investigation indicated that significant changes in the volume and shear strength of a partially saturated Black Cotton soil would accompany slight variations in the moisture content of the soil when the degree of saturation is below 80%. Equations relating soil suction with compression index “cc” and shear strength “t_f” were developed for the Black Cotton soil. The data obtained from the experimental programme also emphasize that, for design of pavements, especially in arid and semi-arid regions, one must consider not only material changes but also potential significant changes in soil suction for the material. From the results, a more accurate prediction of the magnitude and rate of consolidation settlement, in advance of construction for Black cotton soil at a specific state of soil moisture can now be determined.

Keywords: Compressibility, Soil suction, Black Cotton soil, partially saturated soil, stress-strain tests

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