Geotechnical Assessment of Road Failures in the Abakaliki Area, Southeastern Nigeria

The impact of the Abakaliki Shale on the incessant road and highway failures in the Abakaliki area, southeastern Nigeria, has been investigated. Soil classification tests conducted on the shale samples which serve both as subgrade and aggregates showed that the shale classifies as A-7-6 and CH soils, according to the AASHTO and USCS classification systems respectively. A comparison of some of the tests results with the Nigerian Specifications and literature reveals that the Abakaliki Shale neither satisfies most requirements as fill and embankment, nor the requirements as sub-base course and base course material. The unsatisfactory behaviour of the shale as road material (as predictable of an A-7-6 or CH soil) is mainly due to its high plasticity, which simply indicates susceptibility to expansion on moisture influx, and high percentage of particles passing No. 200 British Standard sieve, which is significantly above the recommended limit. The shale, however, satisfies few specifications such as maximum dry density, optimum moisture content and soaked California Bearing Ratio, implying that it’s appropriateness for use as road material could be improved by stabilization and prevention from excessive moisture influx. The results of this research will, to a great extent, assist the civil engineers in the area in designing and constructing roads and highways that can stand the taste of engineering time. Index Term-Abakaliki Shale, Construction material, Geotechnical properties, Road Pavement failure, Nigerian specification.

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