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The foundation soils (subgrades) of highways play critical roles in the stability of the overlying pavement. Studies indicate that geological considerations are often neglected during highway design and construction. This study therefore probed into the cause of persistent failure of a major highway in North-central Nigeria from a geological standpoint with particular focus on the subgrades. The study aimed at characterizing the subgrade soils underneath the pavement and determining optimum conditions for improving it if required and to establish empirical relationships between evaluated properties. Petrographic study was conducted on the parent rocks underlying the pavement to determine the major rock forming minerals in the rocks, while geophysical surveys involving multichannel analysis of surface waves (MASW) was carried out to determine the subgrades’ stiffness. The geotechnical tests involved grain size distribution, Atterberg limits, compaction, California bearing ratio (CBR) and unconfined compression test at varying lime percent addition and curing time. The clay and non-clay minerals in the subgrades were determined through XRD test. Modal composition of rocks revealed that high amounts of feldspar (40–50%), biotite (30–35%) and low quartz (10–15%) dominate the mica-schist that underlies the road’s failed section causing the preponderance of clays in subgrade soil. This is in contrast with the moderate feldspar (25–40%), low mica (10–15%) and high quartz (45–55%) that dominate the granite-gneiss underlying the stable section. The foundation soils of the unstable and stable segments are respectively characterized by low (183–258 m/s) and high shear wave velocity (393–440 m/s) which correspond to loose and stiff subgrade soils. The XRD results showed the presence of clays that have swelling potentials upon contact with water which are notably absent in the subgrades of the stable section. Subgrade soils consistency in terms of Unconfined Compressive Strength (UCS) of the failed section improved significantly from soft (< 50 kN/m2) to stiff (> 100 kN/m2) upon 5% lime and 7 days of curing time. Metrics for model evaluation revealed good models with high R2-Score (0.77–0.8) and low Mean Absolute Error (MAE) of 1.34–1.84. A good coefficient of correlation (r) between modelled CBR and laboratory CBR (r = 0.71–0.89) was also obtained. The study demonstrated that geological studies are paramount not just to provide insights into highway failures but to aid in optimizing the design and construction of healthy and long-lasting pavements as well as preventing continuous future occurrences of failure.Article highlightsGeological considerations are paramount in highway designs and rehabilitation.Swelling clay minerals in subgrades pose significant distress to overlying pavement when wet.Shear wave velocity of subgrades is highly correlated with their stiffness and strength.Treatment of problematic soils with desirable lime amount and curing can significantly improve soil consistency.

The hydraulic characteristics of aquifers in Lokoja and Patti Formations were investigated using combination of vertical electrical sounding (VES), pumping and laboratory tests. A total of 20 VES (10 each in areas underlain by Lokoja and Patti Formations) were carried out at different locations with 5 pumping tests around VES stations in order to determine the geoelectric layers, thickness, depths to water table and groundwater potential of the area. 21 samples extracted fromaquiferous units of surface outcrops were also subjected to laboratory constant head and falling head permeameter tests in order to determine hydraulic conductivity (K) values using the Darcy’s law of liquid flow. The results of VES for areas underlain by Lokoja and Patti Formations revealed 4-5 geo-electrical layers. The depths to water table vary from 5.91-40.8 m. Thickness values are within the range of 7.37-27.3 m for aquiferous units of Lokoja Formation, and 10.8-20.1 m for the Patti Formation. The results of aquifer characteristics using Dar-Zarrouk Parameter gave hydraulic conductivity (K) values between 1.92-91.7 m/day and 2.15-31.8 m/day for aquifers of Lokoja and Patti Formations respectively. Transmissivity (T) values of the aquiferous units of Lokoja Formation fall within 24.97-2117 m /day, while those of Patti Formation vary from 27.9-456.91 m /day. There is a strong correlation between the values of measured and calculated hydraulic conductivity and transmissivity between measured and calculated transmissivity for the five wells (R = 0.99 and 0.92, respectively). Based on the results obtained and interpretations proffered, aquiferous units in both formations are capable of yielding optimum groundwater for private consumption and partly to small communities, and to some extent can supply water for great regional use. It is suggested that similar study should be carried out in other sedimentary basins where to aid regional planning and management of groundwater resource.

This research work focuses on detailed analysis of the sedimentology, mineralogy and paleodepositional environment of the outcropping basal conglomeratic unit of the Lokoja Formation, Southern Bida Basin.  The methods employed are petrographic, sieve and pebble morphometric (particle size) analysis.  Result from the petrographic analysis shows that the minerals contained in the samples of sandstone are largely feldspar and quartz with quartz having the majority composition. This indicated the provenance of the sediments as volcanic-plutonic rock or preexisting sedimentary rock. The grains exhibit angular to sub-angular shapes; suggesting short transportation history and closeness to source area. The sieve analysis result showed that the sediments are mostly coarse grained, poorly sorted, platykurtic and negatively skewed. This implies that the coarse sandstone component of the basal conglomeratic sandstone in the study area probably occurred as a result of sediment being carried by forceful fast-moving water. In poor sorting there is poor porosity which may infer poor reservoir characteristics of the sandstone sediments. The morphometric analysis revealed the paleoenvironment of the pebbles was a river environment based on the scatter plot of MPSI against OPI and plot of FI versus MPSI for the analyzed pebbles.              

Hydrochemical character of groundwater samples from a part of North-Central Nigeria has been investigated to decipher the physicochemical properties, sources of dissolved ions, hydrochemical facies, factors influencing the groundwater chemistry as well as the suitability of the waters for drinking and irrigation purposes. Sixty-seven (67) groundwater samples from hand-dug wells and boreholes were subjected to major ions and heavy metal analyses. The results were further analysed and studied using Pearson’s statistical correlation, ionic ratios and variation plots. The Pearson’s statistical correlation shows that there exists a very strong correlation between water hardness (TH) with Ca 2+ (0.99) and Mg 2+ (0.91), this indicates that both ions originate from similar sources. The ionic ratio plots of HCO 3 and Mg/Na versus Ca/Na; Ca 2+  + Mg 2+ /HCO 3 −  + SO 4 2− ; (Ca 2+  + Mg 2+ ) vs total cations (TZ); (Na + K) vs total cations (TZ) revealed that both carbonate dissolution and silicate weathering serve as major contributor of ions to groundwater chemistry in the study area. Piper and Schoeller’s plots revealed that majority of the water samples are of CaHCO 3 type, and few NaHCO 3 and CaCl 2 types. Gibbs plot suggested that chemical weathering of rocks, ionic exchange and secondary carbonates dissolution and precipitation influenced the groundwater chemistry. Comparison of the concentrations of the ions to World Health Organization (WHO) and Standard Organization of Nigeria (SON) showed that they are generally within permissible limits and therefore suitable for drinking purpose. Irrigation parameters such as, electrical conductivity, sodium adsorption ratio, Wilcox ratio, residual sodium carbonate (RSC), sodium solubility percentage (SSP), magnesium ratio/hazard (MR), permeability index (PI), Kelly ratio/index (KI), all revealed that > 90% of water samples fell into suitable, good and excellent water class and are thus generally suitable for irrigation purposes.

Geotechnical data were complemented with geophysical investigation and employed to delineate problematic soils in parts of Kosofe Lagos, Southwestern Nigeria. The study area was chosen because of known issues regarding cracks in buildings and differential settlement of infrastructures founded on soils in the area. The aim is to generate profiles and maps of the spatial distribution of the subsurface soils to aid in foundation planning. Forty-eight borehole logs and nine Vertical Electrical Soundings were compiled to delineate the different subsurface lithology which include peat, clay and sand. The results showed that the peat layer has maximum thickness of about 18.25 m but absent in some boreholes. This is underlain by clay unit with thickness ranging between 2.50-28.50 m. Sand unit constitute the third layer delineated with maximum thickness of 14 m. There is a general thickening of peat soils in the northern parts, especially around the streams in the area, which is instructive on the role of stream in the formation of the peat. The clay on the other hand is thickest around the northeastern and southeastern parts. The soil profiles generated reveal that the area is underlain by thick peat and clay having significant lateral, vertical variation and rapidly changing lithological facie over short distances. The extensive occurrence of these poor engineering soils calls for adequate engineering precaution in designs of building foundations.