Abstract
Geochemical, geotechnical, and geophysical investigations were carried out along Migmatite gneiss underlain Iyere – Ipele pavement (under construction) in order to assess the suitability of the imported subgrade soil. Also static water level (SWL) was obtained from five open wells along the highway. The geotechnical tests include specific gravity, grain size analysis, consistency limits, consolidation, compaction, and California Bearing Ratio (CBR), and shear strength; while geochemical tests were analyzed using X-ray fluorescence and Atomic Absorption Spectrophotometer (AAS). The results show that SiO2, Al2O3 and Fe2O3 constitute an average of 46.2%, 23.30% and 26.54% respectively of the soils chemical composition. The silica- sesquioxide ratio of the samples ranges from 0.89 to 0.96 and classified as true laterite. The topsoil along the highway is made of moderately competent/competent soil with resistivity ranging from 298 – 924 ohm-m and thickness of 3.1 - 8.2 m. The SWL varies from 3.3 - 5.5 m with an average of 4.3 m (moderately low). The soils are characterized by high California Bearing Ratio values, moderate shear strength (150 – 200kpa), and unconfined compressive strength (300 – 420kpa) with predominant kaolinite clay mineralogy group. The AASHTO and USCS classification system rate the soils as good and fair/good respectively.
Highlights
The frequently distinct engineering behaviour of naturally occurring construction materials within subtropical and tropical regions, as compared with those in temperate zones, has been identified as a key factor in determining the long-term engineering success or failure of road projects in developing countries [1] and is a function of the impact of their interaction with the road environment and the weathering processes
For an elevated highway this will be below the embankment fill and for at-grade sections this would be immediately below the pavement section (Fig. 1)
Where good material sources are available, embankment materials falling between the classification of A1-a and A-4 per AASHTO M145 are preferred
Summary
The frequently distinct engineering behaviour of naturally occurring construction materials within subtropical and tropical regions, as compared with those in temperate zones, has been identified as a key factor in determining the long-term engineering success or failure of road projects in developing countries [1] and is a function of the impact of their interaction with the road environment and the weathering processes. The character of in situ sub-grade material is determined by the geological and weathering conditions of the soil-rock profiles underlying the road. Where a good source is not readily available, stabilization of existing materials should be considered This project work deals with the engineering geological assessment of selection and use of naturally occurring materials (in-situ) for pavement construction and earthwork embankments, along Iyere – Ipele roadway (under construction) in Ondo State, Southwestern Nigeria (Fig. 2), which is classified as “Trunk B” road [3], under the ownership and management of Ondo State government. The highway pavement was constructed with/or on the lateritic materials derived from either the in-situ weathering of the underlying lithology very close to the site or brought to complement the existing ones (Fig. 3). Schematic diagram of roadway structural elements [4]
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