Profiles of Problematic Soils and Spatial Distribution: Implication on Foundation Construction in Parts of Kosofe Lagos, Southwestern Nigeria.

Geotechnical data were complemented with geophysical investigation and employed to delineate problematic soils in parts of Kosofe Lagos, Southwestern Nigeria. The study area was chosen because of known issues regarding cracks in buildings and differential settlement of infrastructures founded on soils in the area. The aim is to generate profiles and maps of the spatial distribution of the subsurface soils to aid in foundation planning. Forty eight borehole logs and nine Vertical Electrical Soundings were compiled to delineate the different subsurface lithology which include peat, clay and sand. The results showed that the peat layer has maximum thickness of about 18.25 m but absent in some boreholes. This is underlain by clay unit with thickness ranging between 2.50-28.50 m. Sand unit constitute the third layer delineated with maximum thickness of 14 m. There is a general thickening of peat soils in the northern parts, especially around the streams in the area, which is instructive on the role of stream in the formation of the peat. The clay on the other hand is thickest around the northeastern and southeastern parts. The soil profiles generated reveal that the area is underlain by thick peat and clay having significant lateral, vertical variation and rapidly changing lithological facie over short distances. The extensive occurrence of these poor engineering soils calls for adequate engineering precaution in designs of building foundation

Geophysical assessment of subsurface conditions at proposed building sites: implications for foundation failure and building collapse

Building collapse has been a recurrent environmental hazard in Nigeria in the last two decades. This is a corollary of inadequate foundation investigation prior to construction, poor government policies, and general lack of awareness on the importance of geophysical and geotechnical investigations. In this study, geological mapping and detailed geophysical investigation using Electrical Resistivity Imaging (ERI) and Vertical Electrical Sounding (VES) were carried out to understand the suitability of proposed building sites at the main campus of the Olabisi Onabanjo University (OOU), Ago-Iwoye, Nigeria for construction. Both Wenner array and dipole-dipole were used for profiling and Schlumberger for sounding. Four transverses and VES were used in each of the three areas investigated. Our results show that the subsurface of the study areas is underlain by Precambrian basement rock of Nigeria. Rocks in the study area include banded gneiss, porphyroblastic gneiss, biotite-hornblende granite and quartzite schist. The sounding stations across the three areas and 2D resistivity imaging revealed three principal geoelectric layers, the topsoil, the weathered layer and the fractured/fresh basement with varied resistivity values for each layers. At the VES stations, the three geoelectric layers have resistivity values of 62 to 1182 Ωm, 3.2 to 1360Ωm and 87 to 4680 Ωm. On the 2D resistivity imaging profiles, the resistivity of the three layers varies from 2 to 1182 Ωm, 30to 1360 Ωm, and 40 to 2904 Ωm for the topsoil, the weathered basement, and fractured/fresh bedrock. Our work demonstrates that some of the proposed sites are structurally incompetent for engineering or foundation purposes. Excavation of the topsoil and reinforcement are required to sustain the proposed structures

Heavy metal characteristics of groundwater in Ibadan South Western, Nigeria

Water, an essential commodity is consequently being affected by natural and human activities. Investigations were made on groundwater of the study area to evaluate the impact of heavy metals. Groundwater samples were collected and analyzed using Inductively coupled plasma- emission spectrometry method, at Acme laboratories Canada. Geochemical analysis revealed a significant concentration of increasing order K > Ca > Mg > Fe > Zn > Cu > Pb > As > Cd. Ca, Fe and K were above the WHO standard. Index of geo-accumulation (Igeo), revealed no contamination of the trace metals. Inter-elemental analysis showed a strong correlation between Cd to Zn (‘r’- 0.983) and Fe to Pb (‘r’- 0.900), indicating that the metals are governed by the same geochemical factors and are from the same anthropogenic source. Piezometric map revealed southwest direction of groundwater flow that shows direction of contamination influx. The study can then be concluded to be contaminated with Ca, Fe and K due to the impact of man’s activities in the environment. Public health effect of these metals could be anemia, kidney damage, brain damage, cancer and ultimately death.Key words: Water, contamination degree, geochemical factors, public health, heavy metal

Integration of magnetic residuals,derivates and located euler deconvolution for structural and geologic mapping of parts of the precambrian gneisses of Ago-Iwoye, Southwestern Nigeria

Ground based magnetic survey conducted between longitude 06O 55I 51IIN –06O 55I 54IIN and latitude 03O 52I 06IIE –03O 52I 4.8IIE (Olabisi Onabanjo University) remarkably revealed a consistent subsurface NW -SE structural azimuth of localized discontinuities within the shallowly buried heterogeneous basement rocks, which at exposed locations are composed of strongly foliated granite gneiss and migmatite-gneiss with veins and veinlets principally orientated in NNW –SSE direction.Magnetic survey of the area was preceded by site inspection to avoid metallic objects interferences. Field procedure in the area involved Cartesian gridding, base station establishment, data acquisition at gridded points, and repeated bihourly diurnal checksat the base station. At the processing stage, diurnal variation effect was aptly removed before subjection to Kriging (gridding). The gridded data was then prepared as input for Forward Fourier Filter Transform (FFT), which upon definition and implementation enabled Butterworth filtering of isolated ringing effects, reduction to the equator (RTE) for geomagnetic correction, and the use of Gaussian and Upward Continuation filtering for regional magnetic intensity trend determination. Removal of the regional magnetic intensity (RMI) from the total magnetic intensity (TMI) resulted in the derivation of the residual anomaly. Enhancement filters adopted for better resolution of the residual magnetic gradient include analytical signal (AS), tilt-angle derivative (TDR), vertical derivative deconvolution (VDD), and the first vertical derivatives (FVD).TMI and RMI values range between 32925nT –33050nT and 32935nT –333050nT respectively, while the residual gradient ranges between 15nT/m and10nT/m; AS ranges between 0.28nT/m and4.1nT/m; and TDR ranges from-1.4nT/m to 1.4nT/m. Source depth calculation estimated from power spectrum analysis and Euler deconvolution ranges between 1m and15m. Composite overlay of magnetic maps revealed jointed and faulted zones within the area; exhibiting a NW-SE principal azimuth of Liberian orogenic impress, which are in consistence with the foliation direction of the jagged foliated bedrock with an estimated maximum overburden of about 15m.The structural significance of this area as a prospective hydro-geological centre, and as an undesirable spot for high-rise building has been accurately evaluated from research findings. Application of integrated geophysical approach, complemented by detailed geological studies may furnish greater information about the subsurface structural architecture.Keywords:Gneisses; Ground Magnetic Surveying;RTE;Structural discontinuities;TDR.1INTRODUCTIONStructuralmapping is an integral part of geologic surveys. It involves measurements, analyses, interpretation and recognition of geometrical features (structures) generated by rock deformations [1]. These structures often serve as fountains of environmental challenges or unparalleled opportunities depending on their modesof occurrences, which in most cases are imminently controlled by the dynamic interplay of differential stress distributions within the earth interior. In line with the principle of uniformitarianism, a broad understanding about Earth’s paleo processes and internal workingsare deductible from the various deformation types for diverse applications. Deductible inferences from brittle deformationsinclude the kinematics of crustal blocks, orientation of principal axes of regional and local stresses, and geometry. Deeper insights indeep seated stresses, regional movements and block motions are obtainable from ductile deformations

Integrated geophysical assessment of a municipal waste disposal site for its geological suitability in terms of the underlain material

Dumpsites are major sources of groundwater pollution as a result of leachates that drain out of the decomposed waste. If there are no underlain materials that could serve as a seal to stop the percolation of leachate, it finds its way to the groundwater. A properly designed landfill is expected to have a high leachate curtailment capacity to limit groundwater pollution. A suitable landfill is expected to have a specific thickness of clay which acts as a natural filter. This study aims to determine the subsurface material and the leachate curtailment of Oke–Diya dumpsites. Very low frequency-electromagnetic method was adopted as a reconnaissance survey, after which electrical resistivity and multichannel analysis of surface waves (MASW) methods were carried out. The resistivity values obtained were used to determine the lithological units of the study area while the MASW was employed to determine the seismic wave arrival times which was processed to obtain the shear wave velocities of the subsurface. The rigidity moduli were also obtained from the shear wave velocities, from which the lithological units of the subsurface were inferred. The integrated method appeared to be the ideal tool to characterize the dumpsite and adjudge the leachate curtailment capacity. The methods corroborated each other. Oke-Diya dumpsite, from the results, revealed the study area had low leachate curtailment capacity and should be evacuated

Physicochemical assessment and bacteriological studies of hand-dug wells of major markets in south western, Nigeria

Rapid population in developing nations has imposed stress on groundwater resources, thus the need to assess physicochemical and bacteriological impact of microbes on hand-dug wells along some major markets in Ibadan Southwestern Nigeria. Water samples from hand-dug wells were measured sequentially, and total dissolved solute (TDS), pH, electrical conductivity (EC), salinity, and temperature were measured in situ. Water samples were analyzed at a Microbiology Laboratory. Most probable techniques used for micro-organism analysis were in three stages: presumptive test used for confirmation of Escherichia coli, confirmed test for total viable bacteria count (TVBC), and complete test to reconfirm the presence of coliform. Presumptive test showed high rate of E. coli in most of the hand-dug wells with (37.5 %). Confirmed test revealed Staphylococcus aureus to be 25 %, followed by Proteus vulgaris (14.6 %), Bacillus species (12.5 %), Pseudomonas aeruginosa (8.3 %), and Klebsiella spp. (2.1 %) respectively. Total viable bacteria counts are 500 to 192,000. Physicochemical results (total dissolved solute (TDS), pH, electrical conductivity (EC), salinity, temperature) when compared with WHO (2006) and SON (2007) revealed all the parameters to be within the permissible limits except pH (5.8 to 9.56), and high values of the parameters were caused by organic matter. High E. coli in the study area revealed influence of human and animal fecal that coul

Non-Invasive Geophysical Investigation of Failure Along a Section of Ago-Iwoye Market Road, Ago-Iwoye, Southwestern Nigeria

A detailed geophysical investigation was carried outto determine ifthe subsurface geology is responsible for the failures along this road section. This study aims to imageand identifycompetent, moderately competent,and incompetent zones of the subsurface soiland thus to findout ifgeology is responsiblefor the failure along this section of the road.Electrical Resistivity Imaging (ERI) using the Wenner array 2D Imaging, and Vertical Electrical Sounding (VES) using the Schlumberger array were adopted for this survey. The geoelectric section from the VES revealed the presence of 3 lithological layers; topsoil, weathered layer (clay, sandyclay, clayey sand),and basement,which is also true for the electrical resistivity images revealed by the 2D electrical resistivity imaging. The results showed that the shallow subsurface beneath the road section is mostly underlain with clay thatis geotechnically incompetent andnot suitable for construction. The causes of road failure are believed to be theresult of the incompetent clayey topsoiland theweathered layer seen inthe profiles, which expand whenabsorbing water and shrink when drying, thuscausing instability beneath the pavement due tothe low shear strength and high compressibility,and also due to fractured basement rocks at shallow depths

Evaluation of Electrical Resistivity Anisotropy in Geological Mapping - A Case Study of Odo Ara, West Central Nigeria.

The study of electrical resistivity anisotropy in rocks has become important in increasing the accuracy of geological mapping using electrical resistivity survey. The study area, Odo Ara near Egbe, west central Nigeria, has been surveyed using electrical resistivity soundings. Sixty Radial Vertical Electrical sounding (RVES) measurements were carried out in the study area which comprises of the banded gneiss, amphibolites, schist and intrusive pegmatites. The aim of the study is to use the electrical resistivity anisotropy properties of the area to resolve its geological setup. The VES data showed a significant presence of electrical resistivity anisotropy. The VES curves obtained were predominantly of 3 geoelectric layer of H-type (ρ1>ρ2<ρ3) curves; the topsoil, sandy clay/ clay layer and fractured basement. The pseudo-sections show a good correlation with the geoelectric section. Moreover, the iso-resistivity and isopach maps also show a significant correlation with the lithological and strike of the rocks in the area but due to the non uniqueness of electrical resistivity, the lithologic difference between the banded gneiss and the amphibolite at the south western part of the area could not be totally resolved. However, the combination of the anisotropy polygons and the iso-resistivity map has reduced the ambiguity inherent in using a single geophysical parameter.Key words: Electrical resistivity anisotropy, radial vertical electrical sounding, anisotropy polygons

Depth estimates from a ground magnetic survey across a North- South trending geologic structure in a part of the basement complex terrain of Ilorin, west of central Nigeria

No Abstract.Global Journal of Pure and Applied Sciences Vol. 13 (2) 2007: pp. 209-21

Paleoenvironmental and paleodepositional architecture of SAMO field in Niger-Delta Basin of Nigeria using seismic and well log data

The use of Seismic data and well log data within the context of sequence stratigraphy is a valuable tool for the recognition of ancient cycles and sequences because they reflect information on the different processes that deposit sediments in different palaeoenvironment. An integrated geophysical well log data and seismic data from our wells within the SAMO field have been utilized to delineate the upper Miocene-Pliocene depositional environment parts of the Niger-Delta Basin. Identification of the different lithologies and depositional environment present in the penetrated borehole was achieved using gamma ray log. This enables the establishment of different rock units in the well from the gamma ray log values and signatures. Three succession signatures which include; the bell, cylindrical and the funnel being more prominent were identified from the log motifs in the different sand bodies attenuated in the wells from the field. The mapped sequences generated Low stand System Tracts (LST) progradational, Trangressive System Tracts (TST) retrogradational and High stand System Tract (HST) aggradational packages. All these reflect the depositional systems that dominated the different phases as a result of base level changes. Furthermore, values quantified from the logs revealed that porosity and permeability are more prominent in places where sand bodies accumulated in the slope channel setting indicative of slope-fills and turbidity fans. This deep-sea channels and switch complex fault system suggest good hydrocarbon bearing potential associated with the distal Niger-Delta province. Also a good quality reservoir was inferred from the sands of both LST and HST while the shale of the TST could serve as a good reservoir