Geotechnical Appraisal and Geological Influence on Road Failure: A New Perspective in Geotechnical Engineering

Abstract

Four samples of red tropical soils (RTSs) were obtained were obtained along 164 km Benin-Auchi-Igarra Highway at notable points/places which include Etete (Benin City), Sabo (Auchi), Ikpeshi and Igarra with the aim of determining their geotechnical properties in ascertaining the causes of the incessant road failure often recorded along the road network as well as the geology of the environment. The tests carried out in accordance with the British Standard Institution (BSI), Unified Soil Classification System (USCS)and American Association of State Highway and Transportation Officials (AASHTO) include; Atterberg limits tests, particle size distribution (PSD), specific gravity (Gs), compaction characteristics and California Bearing Ratio (CBR).Based on USCS classification, Etete (Benin City), Sabo (Auchi) and Ikpeshi have high percentage of sand with little silt (silt sand) whereas Igarra soil contains more of silt with little sand (sand silt). Conversely, AASHTO classification puts Etete (Benin) and Ikpeshi as A-2-4, Sabo (Auchi) as A-3 and Igarra as A-2-7, respectively. These classifications are good to excellent but cannot be applied as sub-base nor base course for roads construction because of their mineralogy and or chemical composition. However, they are better material for sub-grade; hence, result values from Benin, Auchi and Ikpeshi can serve as a good sub grade material, while Igarra soil can serve as a sub-grade material for class S1 road designed to have a minimum thickness of 250 mm. Ultimately, it is advised that soils with low bearing capacity should be stabilized by compaction in order to yield maximum strength on the dry side of their respective optimum moisture content (OMC). The study concludes that the incessant road failure is attributed the wrong uses of TRSs as sub base and base course and non-consideration of the geological influence of the source material.