AKINTORINWA OLAOLUWA JAMES
Publication
Geoelectric investigation of Iwaro-Oka, SW Nigeria was carried out with the aim of evaluating its groundwater potential for future groundwater development. The area is underlain by Precambrian Basement Complex of southwestern Nigeria with local geology essentially made up migmatite gneiss. Thirty-nine (39) Vertical Electrical Soundings (VES) using Schlumberger configuration were acquired. The VES curves were interpreted quantitatively using partial curve matching and computer assisted 1-D forward modeling. Three distinct geologic layers were delineated within the area. These are topsoil, weathered layer and basement rock. The topsoil is generally thin with no hydrogeologic significant. The weathered layer constitutes the major aquifer unit with thicknesses generally less than 10 m. This layer is predominantly composed of clayey material with resistivity values generally <100 ohm-m. The permeability is low with tendency for low groundwater yielding capacity. The overburden thicknesses vary from 1.1 to 23.5 m but are generally less than 10 m. The fracture density in the area is very low. Out of the thirty-nine VES stations occupied within the area, none show evidence of a fractured basement. The groundwater potential rating of the study area is classified as of low based on relatively thin and clayey aquifer unit.
Electrical Resistivity method involving Vertical Electrical Sounding (VES) have been used to evaluate the groundwater potential and aquifer protective capacity of the overburden units within Zion Estate area. Sixty-eight Vertical Electrical Soundings were carried out using Schlumberger configuration with AB/2 varying from 1 to 65 m. The generated geoelectric section from the interpretation of the sounding curves revealed four layers - the top soil, the weathered layer, the partially weathered/fractured basement and the fresh basement. The weathered layers constitute the major aquifer unit in the area but are generally thin. The groundwater potential map revealed that about 85% of the study area falls within the low groundwater potential rating while about 10% constitutes the medium groundwater potential rating and the remaining 5% constitutes high groundwater potential rating. Hence the groundwater potential of the area is generally rated to be low. The overburden protective capacity map of the study area shows that about 75% of the area falls within the poor overburden protective capacity, while the remaining 25% constitutes the moderate/weak protective capacity rating. This suggests that the area is characterized by low longitudinal conductance which informed weak protective capacity rating of the area. Therefore the study area can be vulnerable to pollution from contaminant sources such as industrial waste, septic tanks, underground petroleum storage tanks and landfills when located close to the study area.
This study reports a geophysical survey involving the electrical resistivity method utilizing the Vertical Electrical Sounding (VES) and Electrical Imaging techniques conducted around the distressed walls of a School building with the aim of studying the causes of distress in the walls and characterizing the soil conditions of the area. A total of 20 Vertical Electrical Sounding (VES) stations were occupied using Schlumberger Configuration with AB/2 varying from 1 to 65 m. In the electrical imaging, dipole-dipole array was adopted and the two traverses were occupied in the S-N and E-W directions close to where the wall cracks were manifested. Four geoelectric sequences were delineated within the study area. These include the topsoil, weathered layer, partially weathered/fractured basement and fresh basement. Two linear features (suspected fault) were identified by the electrical imaging on bedrock along the S-N direction. Results identified differential settlement resulting from incompetent subsoil materials and faulted bedrock as possible failure cause.
Aim: Computer software was developed for seismic refraction data interpretation and computation of engineering parameters as a means to ease the problem of cumbersomeness of the manual interpretation of seismic refraction data and computation of engineering parameters by adopting seismic refraction method of investigation. Study Design: Software development. Place and Duration of Study: Department of Applied Geophysics, Federal University of Technology, Akure, Ondo State, Nigeria, between June 2010 and February 2011. Methodology: Necessary equations for the program were compiled, and the program algorithms were developed, fed into a computer interpreter, debugged and run. The program algorithm was written with Visual Basic Programming Language and the software was designed using Visual Basic tools. Results: The software accepts and interprete Single On Shot and On and Reverse Shot seismic refraction data for planar and dipping interface. The developed software plots T-X graph and compute the layer velocities and thicknesses. Engineering parameters such as Fracture Frequency (n), Rock Quality Designation (RQD), Bulk and Young modulus and Poisson ratio (σ) which are used in subsurface engineering evaluation can also be computed using the software.
nil
Schlumberger array is the most commonly used among other arrays for vertical electrical sounding (VES) and it requires large spacing at both ends for deeper subsurface information. The problem of limited space for spreading in built up areas could lead to incomplete information from deeper depth. In this research, the interpretation results of the VES data acquired using the conventional Schlumberger and modified Schlumberger arrays were compared with view to assessing the effectiveness of the Half Schlumberger array as an alternative to the convectional Schlumberger array at sites with space constraints. Fourteen VES data which were distributed across different lithologies using the Schlumberger and modified Schlumberger arrays with AB/2 varying from 1 to 65m were used for the study. The resulting VES curves from both arrays were interpreted using the partial curve matching technique and computer iteration. The resulting field curves from both arrays were the same and the geoelectric sections across different directions for both arrays display the same geoelectric/geologic sequences with similar parameters. The coefficiency of correlation ‘R’ from the crosspots of the interpretation parameters are approximately equal to 1, indicating a perfect correlation between the interpretation parameters for both Schlumberger and modified Schlumberger arrays, hence, modified Schlumberger array can be said to be a good alternative to the convectional Schlumberger array especially in a space constraint area.
Geoelectrical investigation, involving the Vertical Electrical Sounding (VES), was carried out at eight borrow pit sites within the corridor of the Osogbo – Iwo Highway with a view to estimating the reserve of laterite for the highwayrehabilitation works. The area is underlain by a suite of basement rocks which vary from gneiss/migmatite to schist pegmatised, charnockite, meta-intrusives and fine-medium grained granite. The VES involved the Schlumberger array with half current-current electrode spacing varying from 1 to 65 m. The subsurface sequence beneath the proposed borrow pits is generally made up of four geologic layers comprising the topsoil (which is lateritic in places), laterite,weathered layer and the basement bedrock. The 1st and or the 2nd layer constitute(s) the lateritic layer with resistivity values generally greater than 300 W-m and average thickness varying from 0.8 m to 13.3 m. The areal extent of the investigated sites ranges from 2,368 to 6,056 m2. The estimated volume of laterite deposit at the sites ranges from 3,816 to 59,731m3 . Out of the eight borrow pits investigated, only three (Pits 1, 2 and 6) are considered as viable for mining, from the point of view of the reserve while Pit 3 is considered marginally viable. The remaining four sites (Pits 4, 5, 7 and 8) have low reserve of laterite. The overburden thickness within the proposed borrow pits are generally thin, making open cast mining attractive. This study shows that lateritic soils required for road construction are more developed on schist and charnockitic rocks than on quartzites and granitic rocks.
Remotely sensed and geotechnical data have been used to establish some of the causes of perpetual pavement failure along the Ilesa Akure highway in the southwestern part of Nigeria. Four failed segments and two control stable segments were selected for the geotechnical study. The remote sensing investigation involved the processing and interpretation of Landsat-7 ETM+ images covering the study area and its environ for lineaments. The geotechnical investigation involved grain size analyses, Atterberge Limits, Compaction Test and California Bearing Ratio (CBR) determination. Lineaments were identified across virtually all the failed localities with a predominantly N-S structural trend. The geotechnical properties of the soils beneath the stable and failed segments of the highway show significant overlap which suggests that the cause of road pavement failure along the highway may be due to factors other than or complimentary to the geotechnical factors. The pavement failure may have resulted from suspected near-surface linear (geological) features such as faults/fractures and lithologcal contacts beneath the highway pavement. Clayey substratum and ponded embankment toe could also have contributed to the pavement failure.
