waliu Adeolu | University of Lagos,Nigeria (original) (raw)

Papers by waliu Adeolu

Abstract The renovation of a proposed railway bridge in Akere, North Central Nigeria was investig... more Abstract
The renovation of a proposed railway bridge in Akere, North Central Nigeria was investigated using integrated Geotechnical (SPT) and Geophysical methods (2-D and 3-D resistivity imaging using multi-electrode system and extracted vertical electrical sounding techniques). Frequent flooding from the Niger River on overflowing it’s banks have been washing away the railway section along this section and several engineering foundation precaution taken have proved abortive. Eight traverses of 2-D lines, one 3-D section and sixty four extracted VES data were acquired and interpreted. Inter electrode spacing of 1m and inter traverse spacing of 3m were adopted for better near surface resolution. The subsurface layers were characterized by top soil, clay, clayey sand/sandy clay, weathered/intensely fractured rock, sand and fresh basement. The 8 borehole data earlier acquired were integrated with the 2-D and 3-D Resistivity tomography results. A perfect correlation was obtained for the two techniques. However all the boreholes terminated at shallow depth (5 – 11m), and did not provide information beyond this depth while the Resistivity tomography penetrated to a depth of about 15 – 20m and revealed the presence of structurally weak materials (Clay/Fractured basement) inimical to the foundation of the rail line along the traverses. The 2-D and 3-D resistivity tomography shows that the first aquifer is underlain by clay layer separating the upper aquifer unit from the lower aquifer unit, this was further corroborated by the VES results. The presence of low resistivity subsurface materials compose of clay/clayey sand within a depth range of 10 –17m may accelerate failure of piles along the Railway line. This layer is inimical to the proposed rail line. The depth to the competent soil material along where the failed (10 to 20m) piles were installed varies compared to adjacent regions (3 – 6m). It was therefore recommended that necessary precaution in foundation design to competent layer or to exploit the adjacent shallow competent region be considered. Pile foundation to varying depths within the competent region is recommended and should be socketed and anchored within the basement rock which occur at varying depths within the investigated area. The integration of geotechnics and invaluable multi-dimensional variation of subsurface distribution provided in the geophysical investigation have provided an insightful and lasting solution to the foundation problems encountered.

ABSTRACT Geotechnical and geophysical method have been employed in engineering site investigation... more ABSTRACT
Geotechnical and geophysical method have been employed in engineering site investigation of a flood plain in Ado Ekiti, Southwestern Nigeria in order to appraise the integration of both methods and observable trends that can be used as predictive model for future engineering investigation. Geotechnical methods yield good results for point examination but could be deficient over a wide area, particularly in terrains with complex geologic history. Therefore, this study integrates near surface geophysical exploration methods that can provide continuous lateral and vertical information on materials constituting the subsurface. The geotechnical methods involved six shell and auger boring and twenty four Cone Penetrometer Test points while the geophysical investigation involved 2-D resistivity survey along six traverses. The CPTs were distributed along traverses parallel and perpendicular to the direction of stream flow; along strike of rock. Thus, correlations of CPTs were carried out parallel and perpendicular to the stream flow direction and it is observed that parallel to the direction of stream flow, light variation occurs in the CPT curves obtained. However, perpendicular to this direction variations were observed with the least strength obtained closest to the streams i.e. strength increases away from the stream. Thus, structures built parallel to the stream will be supported by homogenous materials, thereby, reducing the tendency of differential settlement, while those built perpendicular to the stream have greater tendency of settling differentially. The borehole logs obtained indicate a sandier sequence to the west of the stream than to the east. Thus, materials to the west of the stream can be considered as being better foundation materials than those to the east of the stream. The 2-D Resistivity surveys reveal similar results to those of the geotechnical methods. Parallel to the stream, the materials are considered homogenous as observed from the moderate contrasts in resistivity values. However, perpendicular to the stream, the contrast in resistivity values increase, with the lowest values concentrated around the stream. In addition, models obtained for surveys conducted on either sides of the stream differ slightly; however those on each side have greater similarity. This corroborates the observation from the borehole logs that materials to the west of the stream are sandier than those to the east. Correlation of vertical slices from 2-D sections with borehole logs was good indicating that lower resistivity values corresponds to weathered materials while those with higher values correspond to partially weathered / fresh basement materials. Thus, although the CPT could not be extended generally beyond shallow depths, and it is almost impracticable to drill boreholes at very close intervals, geophysical prospecting methods could come handy in reconnaissance site characterization. Furthermore, the use of 2-D surveys will provide ample information on materials in between geotechnical test points, thereby revealing the presence or otherwise of anomalous zones in the study area

Abstract The renovation of a proposed railway bridge in Akere, North Central Nigeria was investig... more Abstract
The renovation of a proposed railway bridge in Akere, North Central Nigeria was investigated using integrated Geotechnical (SPT) and Geophysical methods (2-D and 3-D resistivity imaging using multi-electrode system and extracted vertical electrical sounding techniques). Frequent flooding from the Niger River on overflowing it’s banks have been washing away the railway section along this section and several engineering foundation precaution taken have proved abortive. Eight traverses of 2-D lines, one 3-D section and sixty four extracted VES data were acquired and interpreted. Inter electrode spacing of 1m and inter traverse spacing of 3m were adopted for better near surface resolution. The subsurface layers were characterized by top soil, clay, clayey sand/sandy clay, weathered/intensely fractured rock, sand and fresh basement. The 8 borehole data earlier acquired were integrated with the 2-D and 3-D Resistivity tomography results. A perfect correlation was obtained for the two techniques. However all the boreholes terminated at shallow depth (5 – 11m), and did not provide information beyond this depth while the Resistivity tomography penetrated to a depth of about 15 – 20m and revealed the presence of structurally weak materials (Clay/Fractured basement) inimical to the foundation of the rail line along the traverses. The 2-D and 3-D resistivity tomography shows that the first aquifer is underlain by clay layer separating the upper aquifer unit from the lower aquifer unit, this was further corroborated by the VES results. The presence of low resistivity subsurface materials compose of clay/clayey sand within a depth range of 10 –17m may accelerate failure of piles along the Railway line. This layer is inimical to the proposed rail line. The depth to the competent soil material along where the failed (10 to 20m) piles were installed varies compared to adjacent regions (3 – 6m). It was therefore recommended that necessary precaution in foundation design to competent layer or to exploit the adjacent shallow competent region be considered. Pile foundation to varying depths within the competent region is recommended and should be socketed and anchored within the basement rock which occur at varying depths within the investigated area. The integration of geotechnics and invaluable multi-dimensional variation of subsurface distribution provided in the geophysical investigation have provided an insightful and lasting solution to the foundation problems encountered.

ABSTRACT Geotechnical and geophysical method have been employed in engineering site investigation... more ABSTRACT
Geotechnical and geophysical method have been employed in engineering site investigation of a flood plain in Ado Ekiti, Southwestern Nigeria in order to appraise the integration of both methods and observable trends that can be used as predictive model for future engineering investigation. Geotechnical methods yield good results for point examination but could be deficient over a wide area, particularly in terrains with complex geologic history. Therefore, this study integrates near surface geophysical exploration methods that can provide continuous lateral and vertical information on materials constituting the subsurface. The geotechnical methods involved six shell and auger boring and twenty four Cone Penetrometer Test points while the geophysical investigation involved 2-D resistivity survey along six traverses. The CPTs were distributed along traverses parallel and perpendicular to the direction of stream flow; along strike of rock. Thus, correlations of CPTs were carried out parallel and perpendicular to the stream flow direction and it is observed that parallel to the direction of stream flow, light variation occurs in the CPT curves obtained. However, perpendicular to this direction variations were observed with the least strength obtained closest to the streams i.e. strength increases away from the stream. Thus, structures built parallel to the stream will be supported by homogenous materials, thereby, reducing the tendency of differential settlement, while those built perpendicular to the stream have greater tendency of settling differentially. The borehole logs obtained indicate a sandier sequence to the west of the stream than to the east. Thus, materials to the west of the stream can be considered as being better foundation materials than those to the east of the stream. The 2-D Resistivity surveys reveal similar results to those of the geotechnical methods. Parallel to the stream, the materials are considered homogenous as observed from the moderate contrasts in resistivity values. However, perpendicular to the stream, the contrast in resistivity values increase, with the lowest values concentrated around the stream. In addition, models obtained for surveys conducted on either sides of the stream differ slightly; however those on each side have greater similarity. This corroborates the observation from the borehole logs that materials to the west of the stream are sandier than those to the east. Correlation of vertical slices from 2-D sections with borehole logs was good indicating that lower resistivity values corresponds to weathered materials while those with higher values correspond to partially weathered / fresh basement materials. Thus, although the CPT could not be extended generally beyond shallow depths, and it is almost impracticable to drill boreholes at very close intervals, geophysical prospecting methods could come handy in reconnaissance site characterization. Furthermore, the use of 2-D surveys will provide ample information on materials in between geotechnical test points, thereby revealing the presence or otherwise of anomalous zones in the study area