Groundwater Prospect in a Typical Precambrian Basement Complex using Karous-Hjelt and Fraser Filtering Techniques

Electromagnetic survey was carried out at Ibodi, village, Ilesa in Atakunmosa West Local government area with a view to determining the probable locations for groundwater exploration in the study area. Ibodi falls within latitude 70 35′ 35.21″ North and longitude 40 40′ 48.28″ East. The development and increase in immigrants at Ibodi has necessitated this study. A total of five profiles from North to South directions were occupied. It was discovered that distances (100.0-140.0) m, 40.0 m, 80.0 m and 35.0 m on profiles 1, 3, 4 and 5 respectively revealed fractured zones which are suspected to be the best locations for groundwater prospects in the study area

EFFECT OF CONSTRUCTING HIGH-RISE BUILDINGS WITHOUT A GEOPHYSICAL SURVEY

Subsidence and building collapse has become immense globally which Nigeria is not exempted. Due to increase in the number of people living in urban area and increase in the value of land, high-rise buildings have become preferred choice for people. Some of the high-rise buildings in urban areas have become death traps for the people living within because of cracks, subsidence, transport of water from subsurface to the supporting walls of the building, and finally sudden collapse. People direct the blame on the contractor whenever there are tragic situations like that. Majority believes that the contractor must have used inferior building materials before there can be such situation. The truth is that subsurface is heterogeneous in nature, if proper geophysical survey is not carried out before the building construction starts, the constructed building especially high-rise building might stand the chance of falling into this tragic event. The aim of carrying out this research is to settle the dispute between a house owner along Oda Road, Akure, Ondo State, Nigeria and his contractor. Vivid cracks were seen from a high-rise building after the construction works have finished which made the owner to believe that the contractor has used the inferior building materials for him. Eight Vertical Electrical Sounding (VES) stations were occupied around the house in order to know the subsurface information of the study area. The maximum current electrode used was 300 m with the maximum Geometric Factor of 7069.58. Six VES curves showed H-type (i.e. 3-layer earth model) while the remaining two VES curves showed KH-type (i.e. 4-layer earth model). The overburden thickness information of the study area varied between 14.9 m and 39.6 m with an average value of 28.3 m. This overburden is relatively thick for a high-rise building without an artificial basement before the foundation is laid. The weathered layer isoresistivity varied between 102.8 m and 258 m with an average value of 160.4125 m. This was done in order to know the characteristics of weathered layer in the study area, whether it will permit the transport of water from subsurface to the supporting walls of the building or not. The result showed that the apparent resistivities of the weathered layer’s value constitute little and medium weathering processes with poor potential for groundwater. Therefore, water cannot be transported from the subsurface to the supporting walls of the building. The contractor has his blame because geophysicist should have been invited for geophysical survey before the construction works started. Finally, it was recommended that mega activities like party, playing of heavy acoustic music, manual pounding of yams within the building, use of heavily vibrated machines should be avoided in the building

Electromagnetic Investigation into the Cause(s) of Road Failure along Takie-Ikoyi Road, Ogbomoso.

One of the problems Nigeria has is unreliable road networks which has cause several untimely death and damages beyond recognition to human life. Non-destructive geophysical method involving very low frequency electromagnetic profiling was used to investigate the cause(s) of failure that occurred in the road that was constructed in less than two (2) years. Very low frequency electromagnetic profiling data were taken at 10 m interstation spacing along 2 traverses (the dual lane constructed there). KHFILT software was used for the processing of the data obtained. Conducting bodies which indicate clayey materials or linear geologic features such as faults, fractures, joints, and contact between two rocks were inferred from the interpretation. It was concluded that the road was probably constructed on clayey materials which was supposed to be excavated and refilled with laterites. From another angle, it was viewed that may be the engineers intentionally filled the sub-base with clayey materials during construction in order to get their financial returns which the masses are now paying fo

GROUNDMAGNETIC INVESTIGATION INTO THE CAUSE OF THE SUBSIDENCE IN THE ABANDONED LOCAL GOVERNMENT SECRETARIAT, OGBOMOSO, NIGERIA

Groundmagnetic was used to investigate the cause of the subsidence at an Abandoned Local Government Secretariat, Ogbomoso, Southwestern Nigeria with a view to determining whether the sinking and cracks in the plasterworks experienced at the Eastern side of the study area is due to subsurface features or insufficient use of building materials. The study took place at an Abandoned Local Government Secretariat Ogbomoso, Southwestern Nigeria which falls within latitude 080 09′ 50.6″ - 080 09′ 55.9″ and longitude 0040 15′ 36.1″ - 0040 15′ 42.3″. Proton Precision Magnetometer model GSM-19T was used to carry out the geophysical survey along four traverses in East-West and North- South directions. The traverses length ranges from 70m to 150m with inter station spacing of 10m. The results were presented as groundmagnetic profiles of varying magnetic intensities, groundmagnetic contoured map and groundmagnetic surface map. The basement topography was obtained from the profiles using half-width of the amplitude method. Areas with high magnetic values are the competent zones for construction while areas with low magnetic values are the weak zones. The quantitative interpretation gave the overburden thickness to the top of the magnetic basement rock as varied between 7.0m to 13.0m. Interpretation of groundmagnetic data revealed that the weak zones present at the Southeastern, Eastern and Northeastern part of the study area are the cause for the subsidence that occurred towards the Eastern side of the building. Contrary to the opinion of people that the building contractor used inferior building materials for the construction, we found out that half of the building is constructed on either collapse tunnel, fault or fracture which resulted into the sinking and new cracks in plasterworks experienced at the Eastern part of the abandoned Local Government secretariat

Groundwater Contaminats’ Investigation at Aarada Waste Disposal Site Using Geophysical and Hydro-Physicochemical Approach.

A research on the impact of waste disposal site on groundwater resources was conducted around Aarada area, Ogbomosho, Oyo State, Nigeria using electrical resistivity (vertical electrical sounding) and hydro-physicochemical methods. This study was carried out to map the contamination patches at the subsurface and investigate the contamination level of the various hand dug wells situated in the area. A total of seven VES were carried out with length ranging between 80 to 130m. The hydro-physicochemical analysis was conducted at the peak of the wet season on nine water samples taken from nine different hand-dug wells in the research area. The result obtained from the interpreted VES data revealed leachate plumes at the subsurface in the study area. The outcome of the hydro-physicochemical method revealed hazardously high values of Fe2+, Pb2+, Zn2+, Cu2+ and NO3 - to further support the findings from the VES surve

Vertical Electrical Sounding to Determine Fracture Distribution At Adumasun Area, Oniye, Southwestern Nigeria.

People living in Ibadan, Southwestern Nigeria have started shifting their focus on construction of buildings towards villages that are close to the metropolis. It is therefore imperative to carry out this research in order to recommend the types of structures to be erected at Adumasun area, Oniye, Southwestern Nigeria when the time comes in order to avoid catastrophic failure that might have happened thereafter. The aim of this research is to carry out vertical electrical sounding geophysical survey at Adumasun area, Oniye, Southwestern Nigeria with a view to determining the fracture distribution within the study area. The study area is located between latitude 070 37′ 55.37″ to 070 38′ 00″ North and longitude 0030 11′ 10.2″ to 0030 11′ 16.8″ East. Schlumberger electrode array was employed for the study using R 50 Resistivity meter for the data acquisition. The geoelectric survey comprised of ten depth soundings, with maximum current electrode spacing (AB) of 200m. 40% of the modeled curves are A-type, 50% are H-type, and 10% are KH-type. The geoelectric sections obtained from the sounding curves revealed 3-layer and 4-layer earth models respectively. The models showed that the subsurface layers were categorized into the topsoil, the second layer, and the third layer (where it is present). One-third of the study area showed fresh bedrock while two-third showed fractured bedrock. Areas underlying with fresh bedrock and thin overburden thickness are recommended for the construction of high-rise buildings while areas with fractured basement and thick overburden thickness are recommended for the construction of low-rise buildings. It is concluded that the study area is averagely competent for the construction of high-rise buildings and low-rise buildings depending on where individual builders are located

Interpretation of groundmagnetic data in Oke-Ogba Area, Akure, Southwestern Nigeria

Groundmagnetic method was used to delineate into the subsurface in Oke-Ogba area, Akure, which falls within latitude 070 14′ to 070 19′ North and longitude 0050 06′ to 0050 12′ East Southwestern Nigeria, with a view to determining the competent areas for engineering purposes and the promising areas for hydrogeologic prospects. A total of four traverses were established for the purpose of the groundmagnetic study, and the results were presented as groundmagnetic profiles of varying magnetic intensities. The result of investigation revealed that the intensities and characteristics nature of the magnetic anomalies as expressed by all profiles are indicative of the different rock types producing them. Qualitative and quantitative interpretation of individual magnetic anomaly and geological knowledge of the survey area yielded information on the depth of geological features (e.g. rock contact, faults or fractures), structures and magnetic properties of rock units. From the preliminary interpretation, the existence of some structural features such as a likely fault, fracture and contacts between rocks as well as relatively mineralized zones that might contain magnetic minerals of essential magnetite origin is revealed. It was also revealed that Oke- Ogba area, Akure, Southwestern Nigeria is averagely competent for both engineering purposes and hydrogeologic purposes

IMPACT ASSESSMENT OF SOLID WASTE ON GROUNDWATER: A CASE STUDY OF AARADA DUMPSITE, NIGERIA

A research on the impact of waste disposal site on groundwater resources was conducted around Aarada refuse dumpsite, Ogbomosho, Oyo State, Nigeria using electrical resistivity (Vertical Electrical Sounding) and hydrophysicochemical methods. World Health Organization (WHO) standard was used as yard stick for the hydrophysicochemical method. A total of seven VES were carried out with electrode spacing ranging between 80 to 130m. The hydro-physicochemical analysis was conducted at the peak of the dry season on nine water samples taken from nine different hand-dug wells in the research area. The result obtained from the interpreted VES data revealed leachate plumes at the subsurface in the study area. The outcome of the hydro-physicochemical method revealed hazardously high values of Fe2+, Pb2+, Zn2+, Cu2+ and NO3 -

The groundwater potential evaluation at industrial estate Ogbomoso, Southwestern Nigeria

Vertical Electrical Sounding method was used to map Oyo State industrial estate Ogbomoso with a view to determining the groundwater potential of the study area. Ten Vertical Electrical Soundings (VES) were carried out across the area using the schlumberger electrode array configuration with current electrode separation (AB) varying from 130 m to 200 m. Nine out of the ten modeled curves were H-type where the remaining one was KH-type. The geoelectric sections obtained from the sounding curves revealed 3-layer and 4-layer earth models respectively. The models showed the subsurface layers categorized into the topsoil, weathered/clay, fractured layers and the fresh bedrock. The weathered basement and fractured basement are the aquifer types delineated for the area. Groundwater potential evaluated from the maps (i.e. overburden thickness, anisotropic coefficient, weathered layer isothickness, weathered layer isoresistivity, transverse resistance and bedrock relief maps) revealed that the Southern and Eastern parts of the study area are the most promising region for borehole development. However, Northeastern region of the study area can also be considered as fair for borehole development