n Journal of Emerging Trends in Engineering and Applied Sciences - Permeability characteristic of some sub-grade soils along part of the Sagamu-Ore Highway, southwestern Nigeria

Volume 4, Issue 4
  • ISSN : 2141-7016
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Lateritic soils along a section of Sagamu-Ore highway were accessed for their suitability as sub-grade soils with the aim to determine the geotechnical basis for the observed state of the highway pavement failure. The work was carried out in two major stages; field sampling and laboratory analysis. Field sampling involved the study of physical and geological settings of the area, sample collection which include collection of ten bulk samples and twenty undisturbed samples from trial pits, description and preparation for laboratory tests. Laboratory analyses involved permeability test, grain size distribution analysis, consistency limit test, compaction test, linear shrinkage and clay mineralogical analysis. Petrographic analysis of parent rocks (granite, granite gneiss and porphyritic granite) samples were also carried out by studying the representative parent rock samples collected. The results showed that all the sub-grade soils belong to group A-6 of the American Association of State Highways and Transportation Officials (AASHTO) classification system they are thus fair to poor as sub-grade materials. The average value of the linear shrinkage is 7.8%, thus, the studied soils are good highway soils. The permeability coefficient determined for sub-grade soils range between 2.70x10-6mm/s to 2.32x10-4mm/s for stable locations while for unstable locations they range between 4 to 14 percent and 4.50x10-6mm/s to 9.17x10-5mm/s respectively. Soils below stable locations generally have higher amounts of kaolinite than those below unstable sections, thus an indication that stable locations are better drained than unstable ones. The stability of the pavement in stable locations is thus due to good drainage in the locations. Therefore, the practice of designing road pavement without adequate drainage system should be abolished to reduce or prevent contact between water and sub-grade soils.

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