Browsing by Author "Akinlalu AA"

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    Evaluation of road failure vulnerability section through integrated geophysical and geotechnical studies
    (2017) Adiat KA; Akinlalu AA; Adegoroye AA
    In order to investigate the competence of the proposed road for pavement stability, geotechnical and geophysical investigations involving Land Magnetic, Very Low Frequency Electromagnetic (VLF-EM) and Electrical Resistivity methods were carried out along Akure-Ipinsa road Southwestern Nigeria. The magnetic profile was qualitatively and quantitatively interpreted to produce geomagnetic section that provides information on the basement topography and structural disposition beneath the proposed road. Similarly, the VLF-EM profile was equally interpreted to provide information on the possible occurrence of linear features beneath the study area. These linear features pose a potential risk to the proposed road as they are capable of undermining the stability of the pavement structure. The geoelectric parameters obtained from the quantitative interpretation of the VES data were used to generate geoelectric section. The geoelectric section generated shows that the study area was underlain by four geoelectric layers namely the topsoil, the weathered layer, the partly weathered/fractured basement and the fresh basement. The major part of the topsoil, which constitutes the subgrade, is characterized by relatively low resistivity values (<100Ωm) suggestive of weak zones that are capable of undermining the stability of the proposed road. This therefore suggests that the layer is composed of incompetent materials that are unsuitable for engineering structures. Furthermore, fractured basement was also delineated beneath some portion of the proposed road. Since fracture is a weak zone, its presence can facilitate failure of the proposed road especially when it is occurring at shallow depth. The geotechnical results reveal that most of the investigated soil samples are clayey in nature. Integration of the results demonstrates that there is a good correlation between geophysical results and the geotechnical results. Furthermore, a vulnerability section that divided the road segments into three zones based on the degree of vulnerability was produced. These zones were high, moderate and low vulnerability zones. It is estimated that about 60% of the road segments constitutes moderate degree of vulnerability while 30% and 10% of the segments respectively constitute high and low degree of vulnerability.
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    Integration of geophysically derived parameters in characterization of foundation integrity zones: An AHP approach
    (2020) Bayode S; Akinlalu AA; Falade K; Oyanameh OE
    An integrated geophysical investigation involving Very Low Frequency Electromagnetic (VLF-EM), and electrical resistivity methods using Schlumberger Vertical Electrical Sounding (VES) techniques was conducted at Deeper Life Camp ground, Ipinsa, Akure, Southwestern Nigeria with the aim of developing a model map that will enhance the knowledge of the subsurface geology viz-a-viz foundation integrity for appropriate location of building within the study area. The effect of four factors including soil apparent resistivity at different depths, depth to bedrock, geology and fracture density on engineering foundation were considered. In order to achieve this, a total of ten traverses were established in approximately NW-SE, NE-SW, N-S and E-W directions with station interval of 5 m and inter-traverse separation of 10 m. One hundred and forty eight (148) station positions were occupied in all for the VLF-EM profiling. Also, fifty four (54) VES stations were occupied across the study area with current electrode spacing (AB/2) varying from 1 to 65 m. Hilbert transform, Amplitude analysis, Fraser technique and Q-Factor performed on the VLF-EM method assisted in the delineation of conductive zones that could be inimical to foundation integrity. The VES result delineated four major geo-electric layers within the study area which are: topsoil, weathered layer, fractured bedrock and the fresh bedrock. The thickness of the layers generally ranges from 0.5-19.6 m. Based on geological and geophysical investigations, foundation integrity map of the area was produced using the Multi-criteria Decision Analysis, approach of Analytical Hierarchy Process (AHP). The model map classified the foundation integrity of the study area into very low, low, moderate, high and very high foundation integrity zones. The competency model at a depth of 3 m is adjudged most suitable for foundation in the study area.