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Economic importance of road has increased enormously over the last decades in Nigeria and to a large extent, they are complementary to other modes of transportation. However, the deterioration of a road begins soon after construction. Some of the roads in Nigeria do not last up to 5 years before failure becomes imminent. Road failure has been defined in different ways by various authors. According to [14], a road stretch is said to have failed when a part or all the parts of the road surface or any part of the road structural section or the entire road prism or pavement at any point along the highway is deformed and rendered un-motorable. Highway failure occurs when the road no longer performs its traditional function of providing continuous smooth surface for minimal frictional movement of vehicles. When such failure occurs before the anticipated design life, it is rightfully described as premature [5]. Highway premature failure occurs Abstract Mineralogical, geochemical and geotechnical analyses were carried out to evaluate the contributions of geological and geotechnical properties of subgrade soils to the incidence of failure of the Ipele-Isua road, southwestern Nigeria. Field observations showed that the road is in a very poor state of disrepair as major portions of the road alignment have failed. The road alignment is underlain in places by Quartz Schist, Banded Gneiss and Granite Gneiss. The results of the laboratory tests revealed that the natural moisture content ranges from 6.5 to 23.3%, liquid limit from 20.1 to 55.1%, plasticity index 5.2 to 22.2%. The grain size analysis showed that the amount of fines ranges from 13 to 60.8%. Others are linear shrinkage between 2.9 and 11%, free swell between − 16.67 and 41.94%, maximum dry density from 1520 to 1792.1 kg/m 3 and CBR between 2 and 17%. The specific gravity ranges from 2.51 to 2.63. The major clay minerals present are kaolinite and dickite with dominance in 50% of the samples. Major oxides present are SiO 2 , Al 2 O 3 , Fe 2 O 3 , K 2 O. Na 2 O, MgO and CaO are generally less than 1%. Based on AASHTO classification, 19% of the samples are classified as A-2-4, 33% classified as A-2-6 while 44% classified as A-7. Dominance of low California bearing ratio, low maximum dry density, high linear shrinkage and A-7 soil group expectedly contributed to poor geotechnical properties of the subgrade. Absence of drainage is suspected to have worsened the failure as exhibited on the road.

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Due to the rapid expansion and associated construction of civil engineering structures on the Federal University of Technology, Akure (FUTA) campus, there arose an urgent need for an engineering geological mapping of the underlying soils (residual soils). Generalized geological mapping revealed four types of basement rocks namely migmatite-gneisses, granites, quartzites and charnockites. Results from the fifty (50) soil samples from twenty-five test pits collected all over the spread of the campus coverage of 6.4 km2 revealed that the campus is underlain by soils of granular and clayey composition, generally lateritic, having reddish to brownish colour. Engineering geological tests such as natural moisture content, particle size analysis, consistency limits, California bearing ratio and consolidation were carried out on the soils following standard procedures revealed that the values of natural moisture content do not generally follow a consistent pattern and varied from location to location. The grain size characteristics curve, displayed 84% and 16% subsoils are of well graded and poorly graded type respectively. The soils were grouped into CL (low plasticity), CI (medium plasticity) and CH (high plasticity) from consistency limits results. Compaction characteristics of the subsoils revealed 36% and 64% representative of fair to good and poor to very poor foundation materials respectively. Soils with settlement rates greater than 1mm/year were designated as high settlement subsoils. 72% and 28% of the subsoils fell into hard to stiff and soft categories from the shear strength characteristics respectively, and classified as c-ø soils. California Bearing Ratios values range from 10 – 70, indicating their suitability for pavement construction. Conclusively, areas underlain by migmatite-gneiss and charnockite-derived soils, and granite and quartzite-derived soils possessed low and high strength characteristics respectively which can be attributed to their textural characteristics. The subsoils of the entire campus spread are however capable of bearing very substantial loads.

The inhabitants of Akure Metropolis, southwestern Nigeria, depend solely on groundwater for their domestic, industrial and irrigation purposes. There is a need to delineate recharge and discharge areas for assessment and management of groundwater in these areas. One hundred and ninety (190) dug wells were selected for this assessment. Elevation and water table data aided accurate delineation of recharge, discharge and groundwater divide areas. Thirty-six wells representative of recharge and discharge areas were subjected to pollution assessment [DRASTIC, water quality index (WQI) and runoff potential]. The results revealed that the recharge areas have higher pollution potential and runoff amount than the discharge areas. This implied that groundwater sourced from recharge areas was more pollution prone than that sourced from discharge areas. WQI results revealed that the waters from recharge and discharge areas fall within excellent, good, poor, and unsuitable quality categories. Hydrogeochemical results revealed that concentrations of cations and anions are in order of Ca 2+ > Mg 2+ > K + > Na + and HCO 3 − > Cl − > SO 4 2− with a predominant Ca-HCO 3 facies typifying water from a basement complex environment. Gibbs plot and chloro-alkaline index affirmed the rock dominance and existence of imprints of ion-exchange processes influencing the groundwater quality. Intense weathering activities aided with long resident time spent by the water in the voids of the aquifer media are characteristic in this terrain. Recharge of precipitating water through infiltration into the weathered basement aquifers is a pointer to the greater yield of water in the wells. The possibility that precipitation-weathering process has led to the increase in concentrations of all ionic species and possible pollution of the groundwaters from the recharge and discharge areas cannot be ruled out at all.