AKINTORINWA OLAOLUWA JAMES
Publication
An engineering evaluation of the developing parts of Ondo State University of Science and Technology (OSUSTECH), Okitipupa, Nigeria was carried out using engineering geophysical approach with the aim of determine the competency of the subsurface soil within the area and evaluate its engineering implication for infrastructural development. The Electrical Resistivity Method was adopted. Twenty four (24) Vertical Electrical Sounding (VES) locations were occupied using Schlumberger electrode configuration with AB/2 varying from 1 to 225 m. This was quantitatively interpreted using partial curve matching and computer iteration. The results were used to generate maps, geoelectric sections. Six geologic / geoelectric sequences delineated across the area are the topsoil, medium sand, coarse grain sand, clayey sand, sandy clay, and clay formation. The topsoil exhibits relatively high resistivity while the thickness in excess of 1 m. Based on this, the upper layer can host the foundation of light weight civil engineering structures using strip foundation. Heavy weight civil structures can be hosted within the second layer (coarse sand) using deep foundation, since the resistivity value is in the range of 200 to 1950Ω m. The saturated natureof this layer must be considered in the design of the foundation. Metallic pipes and tanks can be buried within the topsoil with limited threatening of corrosion, since the resistivity values of the topsoil is generally greater than 180 Ωm. There is need for artificial enhancement of the conductivity of the area before an earthing material can be buried within the area.
The growing population and indiscrimate dumping by some resident in Aule informed an investigation into the chemistry of water consumed by the inhabitants. This will enable us assess the quality of water in the area. Hydro-chemical investigations have been used to evaluate the groundwater potential and its portability for human consumption in the area. Water samples were collected from twenty one (21) wells for chemical analysis within the study area. The anions and cations concentration levels of the sampled water falls within WHO recommended, but some are at the upper limit of this recommendation. Based on this, the groundwater within the area is of good quality and hence suitable for human consumption. It could therefore be concluded that the quality of water in Aule is safe for consumption and routine chemical analysis of groundwater from the area should carried out to detect any deterioration in the water quality.
The Aule area has witnessed an influx of people as a result of residential development; hence the need to have access to potable water since water plays a vital role in the day-to-day activities of human beings. To evaluate the groundwater potential of Aule and its environs, a total of sixty five (65) Vertical Electrical Sounding datasets were acquired using Schlumberger configuration with maximum current electrode spacing (AB) of 300 m. The VES data were interpreted quantitatively using partial curve matching technique. The resulting layer parameters (resistivity and thickness) were fed into computer for iterationusing Win Resist software. The results obtained were used to generate geoelectric sections and maps as related to the objectives of the study. Three to four subsurface layers were delineated within the study area which is the topsoil, weathered layer, weathered/fractured Basement and the fresh Basement. The weathered layer/fractured Basement constitute the main aquifer unit in the area, but this layer is relativelythin and composed of high percentage of clay, hence of low groundwater yield. About 95% of the area falls within the zone of low groundwater potential. The overburden protective capacity is majorly poor/weak in most parts of the area except for small portions of moderate protective capacity in the northeastern end of the area.
Landsat EMT+ surface reflectance images of 2002 of the Akure Metropolis wereprocessed to generate geomorphological and lineament maps. Five Hundred and thirteenSchlumberger Vertical Electrical Sounding (VES) data set were quantitatively interpretedusing the partial curve matching and computer assisted 1-D forward modeling. Fourgeomorphological units which include residual hills, pediments, low land pediments andetchplain were delineated. Satellite- imagery-delineated lineaments show predominantlyNNW-SSE, ENE-WSW and NNE-SSW orientations with subsidiary NW-SE and W-Etrends. The VES interpretation results delineate four main subsurface geologic units.These include the topsoil, weathered basement, partly weathered/fractured basement andthe fresh basement bedrock. Two major aquifer units - the weathered basement and thepartly weathered/fractured basement were delineated. Thematic maps of geology,geomorphology, hydro-lineament density, aquifer thickness, and electrical coefficient ofanisotropy were integrated to classify the Akure Metropolis into very low, low, moderateand high groundwater potential zones.
Erosion index map of Akure Metropolis was developed using an integrated remotely sensed, geological and soil data. This was with a view to classifying the metropolis into different erosion risk zones. Administrative andtopographic maps, geologic and soil maps, Landsat ETM+, Aster DEM and thirty two (32) erosion types datawere acquired. Landsat ETM+ was pre-processed for geometric correction, haze reduction and re-sampling.Optimum index factor and covariance analysis were carried out in order to determine the least correlated bandsand these bands were subjected to convolution filters, texture analysis at 3X3 window size, histogramequalization, de-correlation stretch, principal component analysis (PCA) and the Aster DEM to topographicanalysis such as sink fill and shielded relief to generate slope map and lineament map. All the derived mapsincluding the soil map were reclassified and given risk values according to their order of degree of contributionto either accelerate or decelerate soil erosion. Using weighted index overlay raster tool in ArcGIS software, allthematic maps were captured in GIS environment to produce a composite erosion index map of the study area.Existing erosion type data were used to establish the reliability of the erosion index map. The erosion index mapclassified the Akure Metropolis into three zones – very low risk (57.5%); low risk (33.9%) and moderate risk(8.6%). Most parts (91.4%) of the metropolis fell within the very low to low risk zones with tendency forsheet/reel erosional features. Areas with moderate risk with tendency for gully erosion were located on the highslope region.
Five hundred and thirteen Vertical Electrical Sounding data sets were acquired within the Akure Metropolis, processed and interpreted quantitatively. Akure Metropolis lies within Latitudes 07°10. 09 and 07° 19N and Longitudes 05° 07 and 05° 17E and covers an areal extent of about 340 km The soil map of the study area was extracted from existing soil map and subsequently digitized. Geologic lineaments were delineated from satellite imageries acquired for the study area. The VES interpretation results delineate four subsurface layers which include the topsoil, weathered  Basement, partly weathered/fractured basement and the fresh basement. The layer resistivity values for the topsoil used in this study range from 13 – 7133 ohm-m with layer thicknesses of between 0.3 and 5.2 m. Three major soil associations were identified. These include Iwo, Ondo and Itagunmodi Associations. The satellite-imagery-delineated lineaments show predominantly NNWSSE, ENE-WSW and NNE-SSW orientations with subsidiary NW-19. SE and W-E trends. The topsoil resistivity, lineament density and soil thematic maps were integrated in a GIS environment to generate the subsoil competence map which classifies the Akure Metropolis into low competence (3.5%), moderately competent (26.6%) and highly competent (69.9%) zones. The study concluded that most parts (96.5%) of the metropolis are underlain by moderately to highly competent subsoil.
A geoelectric investigation, involving 1-D Vertical Electrical Sounding (VES) with the Schlumberger array and 2D Electrical Imaging with the dipole-dipole array, was carried out at a site proposed for an airport in Ebonyi State. This was with a view to generating near and subsurface images required for the assessmentof the suitability of the site for civil engineering construction works. Fifty six (56) VES stations were occupied along eight (8) traverses while the dipole-dipole profiling was carried out along segments of three of the traverses. The VES curves were quantitatively interpreted and the results were used for the generation of geoelectric sections and isopach map of the lateritic layer. Four subsurface layers were delineated. These include the topsoil (lateritic in most places), lateritic shale, shale/clay and siltstone. The topsoil resistivity values varied from 24-5898 Ωm while the thicknesses ranged from 0.7 - 4.6 m. The lateritic shale second layer resistivities and thicknesses were 101-473 Ωm and 1.6 - 8.3 m respectively. The clay/shale third layer showed thicknesses and resistivity values of 3.6 – 108.3 m and 1 – 98 Ωm respectively. The fourth layer was siltstone with resistivity values ranging from 53 -3170 Ωm. The 2-D resistivity structures delineated two subsurface layers: a merged topsoil/lateritic shale top layer and the underlying clay/shale layer. No subsurface geologic structure was delineated. The high resistivity lateritic topsoil/lateritic shale and the basal siltstone constituted the two competent layers while the low resistivity shale/clay, the incompetent horizon. The upper competent lateritic layer could host light-medium weight civil engineering structures while heavy structures would need to be anchored on friction piles.
