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  • Author: J.O Coker x
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Site Characterization for Construction Purposes at FUNAAB using Geophysical and Geotechnical Methods

Abstract

Geophysical and geotechnical techniques were used to investigate the sub-surface information of a proposed site for a hostel construction at Federal University of Agriculture, Abeokuta. Ten vertical electrical sounding (VES) stations were adopted. Typical sounding curves obtained include the HA, KH, AKH and KQH types, of which the AKH-type consists of 40% of the survey points, and a maximum of five geo-electric sub-surface layers were delineated. Laboratory analyses were performed to investigate particle size distribution, Atterberg limit, compaction limit, California bearing ratio (CBR) and specific gravity. The CBR revealed that all soil samples, except L4, are mechanically stable and have high load-bearing capacity. The Atterberg limit test and the geo-electric section showed that the second layer of VES 4 is composed of sandy clay with high plastic index and low liquid limit, which may pose a threat to the foundation of any engineering structure. VES locations 5, 6 and 8 were identified as high groundwater potential zones suitable for optimum groundwater abstraction. The study area is suitable for both shallow and deep foundations, however VES 4 and VES 5 require reinforcement.

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Estimation of Magnetic Contact Location and Depth of Magnetic Sources in a Sedimentary Formation

Abstract

The aeromagnetic data of Idogo, Southwestern Nigeria, have been used to study the lithology and to determine the magnetic source parameters within Idogo and its environs. Idogo lies between latitudes 6°30′N and 7°00′N and between longitudes 2°30′E and 3°00′E. The magnetic anomaly map, the regional geology, the analytic signal and the local wavenumber were used to identify the nature and depth of the magnetic sources in the region. Data enhancement was carried out to delineate the residual features relative to the strong regional gradients and intense anomalies due to the basin features. The estimated basement depth using the horizontal gradient method revealed depths ranging between 0.55 km and 2.49 km, while the analytic signal amplitude and local wavenumber methods estimated depth to the magnetic sources to range from 0.57 km to 4.22 km and 0.96 km to 2.43 km, respectively. Depth computations suggested the presence of both shallow and deep sources. The total magnetic intensity values ranged from 3.1 nT to 108.3 nT. The area shows magnetic closures of various sizes in different parts of the area trending West, with prominence at the centre and distributed East–West.

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