Fresh Basement Rock Research Articles

An Assessment of Groundwater Potential for Water Supply in Misau and Dambam Local Government Areas of Bauchi State, Nigeria

This study aimed at assessing groundwater potential in Misau and Dambam areas of Bauchi State, Nigeria. Vertical Electrical Sounding (VES) survey was also conducted to carry out the study. Five thematic maps were generated for weighted overlay. Descriptive statistics was used to analysed data on water supply situation, aquifer parameters were analysed using standard table where porosity and permeability were calculated. The VES data was analysed using ipi2win, thematic maps were produced through overlay analysis using extension of ArcGIS 10.4. VES result reveals the existence of about three to four geologic layers in the study area which constitute the topsoil, weathered rock, weathered/fractured rock, fractured basement, and fresh basement rock. Nine out of the thirteen soundings conducted were found to be of good in nature while the only non-promising aquifers were found in Jalam Kukadi, Hardawa PHC, Bada Koshi, Dambam A Bam. Five groundwater potential zones were determined which are very low 354 km2 (15%), low 393 km2 (15%), moderate 416 km2 (20%), high 436 km2 (25%), and very high 497 km2 (25%). Drainage is the most important factor affecting groundwater occurrence with 25% which is the highest followed by geology with 22%. It can be concluded that 50% of the study area was characterized under high, and very high groundwater potential. It is recommended that areas with poor groundwater potentials government and non-governmental organizations should provide them with an alternative source of water to aid them during periods of difficulties.

Modeling of geophysical derived parameters for groundwater potential zonation using GIS-based multi-criteria conceptual model

This study modeled geophysical derived parameters and multi-critically synthesized their themes based on geospatial and analytical hierarchy processes (AHP) approaches for groundwater potentiality prediction mapping. These methodologies were investigated in a typical hard rock geologic terrain, southwestern, Nigeria. Considering the spatially acquired 96 vertical electrical sounding (VES) data in the area, geoelectric sections revealing five subsurface layers including the topsoil, laterite, weathered layer, fractured basement and fresh basement rock were produced mindful of the 2-D resistivity structure subsurface imaging data interpreted results. The correlative results of the 2-D resistivity structure images and VES data interpretation results delineated major low resistivity vertical discontinuity typical of fractured zones characterized with width range of 25–40 m, while the depth vary from about 40 to > 60 m. Themes of groundwater potential conditioning factors (GPCFs), namely: regolith, bedrock relief, hydraulic head, coefficient of anisotropy, aquifer resistivity and aquifer thickness were prepared from the re-analyzed hydrogeological and geophysical data. The produced themes were appropriately weighted in the context of AHP data mining technique. The groundwater potential prediction index (GPPI) mathematical modeling equation for the area was established via applying the weight linear average algorithm involving the AHP weightage results. The synthesized results of the applied GPPI model equation on the GPCFs’ hydrogeologic themes give GPPI values in the range 1.59–3.65 for the study area. The geospatial modeling of the GPPI estimated values result produced groundwater potential prediction index map for the area. The produced GPPI model map zoned the area into low (1.59–2.30), medium (2.30–2.61), medium–high (2.61–3.02) and high (3.02–3.65) groundwater potential classes. The area analysis of the GPPI map indicates that more than 70% of the study area has ‘low to medium groundwater potential. The GPPI map result verification using reacting operating characteristics technique results gave 86% and 81% success and prediction rates, respectively. The findings of this study are useful to water managers and decision-makers for locating appropriate positions of new productive wells in the study area and other areas with similar geologic settings.

Geophysical and geotechnical investigations of the site of a collapsed two-storey building in Modomo, Ile-Ife, Southwestern Nigeria

Geophysical and the geotechnical methods were used to study the site of a collapsed two-storey building in orderto determine the sequence and competence of the subsurface layers and determine the cause of the collapse of the building. The geophysical method employed the electrical resistivity method involving one dimensional (1D) Vertical Electrical Sounding (VES) and the two dimensional (2D) imaging techniques. Three VES stations were occupied using Schlumberger electrode configuration. 2D imaging data were acquired along four traverses using dipole-dipole electrode configuration. The geotechnical method involved Cone Penetration Test (CPT). CPT data was acquired at two points with the aid of 2.5 ton Dutch CPT machine. The results showed four subsurface layers based on the 1D VES results and 2D imaging results namely: topsoil, weathered layer, fractured basement rock and fresh basement rock. The topsoil resistivity varied from 116 Ωm to 191 Ωm and has thickness of about 1.5 m. It was classified as moderately competent. The second layer is weathered rock with resistivity varying between 92 Ωm and 327 Ωm and of about 8 m to 13 m thickness. This layer is also moderately competent. The third layer is fractured basement rock. It underlies the weathered rock and have resistivity varying from 391 Ωm to 405 Ωm. Its thickness varied from about 2 m to 20 m. This layer is competent. The fourth layer is the fresh basement rock having resistivity varying from 1365 Ωm to 12348 Ωm and is highly competent. The subsurface materials in the area are competent and can sustain the foundation of the building. Hence, the study concluded that the building collapse did not result from incompetent subsurface materials. Factors other than incompetent subsoil material that is human factors are believed to be responsible. This study has demonstrated the effectiveness of geophysical and geotechnical investigations in determining the competence of subsurface materials at engineering sites.

Groundwater potentiality in hard-rock terrain of southern Saudi Arabia using electrical resistivity tomography approach

To detect groundwater-bearing zones in southern Saudi Arabia, 10 profiles of 2D electrical have been constructed resistivity tomography at five selected sites. The collected data were corrected and processed using the RES2DINV software. The results demonstrated that site-1 contains two groundwater-bearing zones; the first zone is situated 13 m beneath the ground surface, while the depth of the second zone varies from 4 m to 15 m. A promising 15-m-deep groundwater-bearing zone was identified at site 2. The groundwater-bearing zones exhibit depths of 40, 10, and 10 m at sites 3, 4, and 5, respectively. The detected groundwater-bearing zones are notably shallow, with a depth of 20 m below the ground surface and with lateral extension up to 200 m. These aquifers prevail in the alluvial deposits, where the weathered/fractured or fresh basement rocks underlying these aquifers. Moreover, rainfall recharges these unconfined aquifers, as evidenced by the increasing water levels along the main Wadi channels flow during rainy seasons. Sites 2, 3, and 5 are considered as groundwater-bearing sources with high potential. Because this unconfined aquifer can be swiftly replenished by the 300–360 mm of annual rainfall in the southern Saudi lowlands, it is a promising area for groundwater supply for future urbanization plans and agricultural projects in neighboring areas.

Investigation of subsurface contaminants leachate within Ansaru-Islam Secondary School, Ilorin, Nigeria

This study adopts the use of Vertical Electrical Sounding (VES) and 2-D resistivity imaging (employing Schlumberger and Wenner array configurations) to investigate and map the extent of leachate’s migration and its possible impacts on groundwater within Abata Asunkere dumpsite, Ilorin, Kwara State. This study was inspired by the unrestrained manner of garbage dumping in the area over time, which poses great threat to the availability of clean water for the increasing populace. To delineate the subsurface, 2-D resistivity imaging data were acquired along two traverses, while the VES data were randomly acquired along the established traverses. The 2-D resistivity imaging and VES data were processed using Res2D and IPI2Win software respectively. The results of the 2-D and VES revealed five (5) geoelectric sections, which correspond to the topsoil, clayey sand, weathered basement, fractured basement and fresh basement rocks with H, QH and KH sounding signature curve types. The topsoil has layer thickness of 0.5 - 1.7 m and resistivity values ranging from 11.9 - 165 Ωm. The clayey sand has layer thicknesses between 0.7 - 2.8 m and resistivity values ranging from 20.1 - 56 Ωm. The weathered basement has thickness of 0.9 - 16.3 m and resistivity values ranging from 2.09 - 5.25 Ωm. The fractured to fresh basement has resistivity values ranging from 26.8 - 3000 Ωm with thickness ranging from 5.3 m to infinity. The third layer with low resistivity values of 2.09 - 3.52 Ωm at depth range 0.9 - 10 m is suggestive of leachate contamination. The outcome of this study indicates that some regions around the dumpsite are susceptible to leachate’s contamination, which has tendencies to permeate the unconfined aquifers in the study area if not properly monitored and controlled.

GROUNDWATER POTENTIAL INVESTIGATION USING 1-D ELECTRICAL RESISTIVITY TECHNIQUE AT NIGER STATE POLYTECHNIC ZUNGERU, ZUNGERU MAIN CAMPUS, NIGER STATE, NIGERIA

Electrical resistivity method employing vertical electrical sounding was carried out with aim to investigate groundwater potential at Niger State Polytechnic, Zungeru, Niger State. Ten points were selected at different locations within the campus for vertical electrical sounding (VES), using Schlumberger protocol. Maximum current electrodes separation (AB) of 120m was used. The investigation was carried out using Terrameter PE 02 SAS 300 system. The survey was able to investigate groundwater potential of the area. The IPI2win software was used for data analysis. The geologic section derived from geoelectric parameters revealed three subsurface layers. The first layer is interpreted as topsoil, the second layer is inferred to be weathered rock, while the third layer probably could be fresh basement rock. The thickness of the superficial cover is averagely 2.49m, and the depth to the basement is between 5.2m to 22.9m, the aquifer thickness ranges between 1.67 to 21.1m. The laterite in the second layer shown in some locations is of great importance as it reduces surface run off and aids infiltration into the underlying aquifer. The thickness of the aquifer component in the north-southern half of the study area is large enough to harbour substantial quantity of water. Areas around ZUN 01 and ZUN 05 could be potential areas for groundwater exploration. In this research, the depth to bedrock and aquifer thickness were determined, lithological formations within the overburden were delineated and approximate depths

Geology and Geoelectrical Appraisal of Panda and its Environs parts of Gitata Sheet 187NE North-Central Nigeria

Geological mapping and Geophysical investigations were carried out in Panda and its environs, with the aim of studying the geology (rock types and their structural features; joints & fractures) and its groundwater potentials. The area is underlain by the Basement Complex rocks of the North Central Nigeria consisting of porphyritic granodiorite, migmatized-gneiss and mica schist. The structural features associated with rocks in the study area include; exfoliation, joints, fault, pegmatitic and quartz veins. Twenty eight (28) Vertical Electrical Sounding (VES) were carried out away from cultural interferences. Interpreted data shows a dominance of KH and H type curve. The quantitative and qualitative interpretations revealed weathered and fractured basement. Iso-resistivity of the true aquifer, depth to basement, basement resistivity and, piezometric maps were delineated. Out of the twenty eight VES,only areas within the center of the study area (Kuban SE, Tanga North, Panda market, Jababe, Idur West, Idur and MusheJaba) have been delineated as the most viable locations for good water potentials due to the resistivity value of the rock materials (fractured and weathered basement) around those areas (50Ωm - 200Ωm) and some of the structural features (fractures, joints and faults) which serves as secondary reservoir for groundwater on account of their low resistivity values due to the high conductivity of groundwater that occupies the voids and fissures of the rock. The potential for groundwater in the study area are moderate at AngwanKwaro, AngwanMaje, and Chandap North, Kukuri area where depth to basement is shallow and occupied by fresh basement rocks (porphyritic granodiorite). While the least expected yield lies in AngwanPaa North and GidanSarki North. The two types of aquifer in the study area are weathered basement and fractured basement. This study will serve as guide for groundwater exploration and development in the study area.

Geophysical and contamination assessment of soil spatial variability for sustainable precision agriculture in Omu-Aran farm, Northcentral Nigeria

The spatial and temporal variability of soil properties (fluid composition, structure, and water content) and hydrogeological properties employed for sustainable precision agriculture can be obtained from geoelectrical resistivity methods. For sustainable precision agricultural practices, site-specific information is paramount, especially during the planting season. An integrated one-dimensional (1D) and two-dimensional (2D) electrical resistivity survey have been adopted to characterize the subsoil parameters and delineate the aquifer unit of large farm areas, especially in precision agricultural practices. Also, contamination assessment reveals the soil quality status of farmlands. This study aims to determine the site-specific soil parameters of a commercial farm in Omu-Aran, Northcentral, Nigeria. The subsoil features from the geoelectrical resistivity surveys indicate 3 to 4 distinctive lithology to a depth of 43.4 m into the subsurface of the farm. The ID (Vertical Electrical Sounding) and 2D resistivity inversion models results have revealed the heterogeneity nature of the topsoil, also known as the stone zone comprising of reworked clayey soil and sandy gravelly soil, the weathered/saprolite zone (gravelly sandy/sandy soil), the fractured basement and the fresh basement rock. Contamination factor (Cf), pollution load index (PLI) and Nemerow integrated pollution index (NIPI) were used to assess the contamination index on the farmland. Toxic elements such as arsenic, cadmium, chromium, cobalt, lead, manganese, nickel, and zinc have low to moderate contamination in the farm. The depth of investigation (≤3m) covers the upper root zone of significant crops grown in the area. The findings can assess soil contamination, delineate basement features, subsoil variability, soil profiling, and determine the subsoil hydrological properties.

Hydrogeological Investigations in Basement Terrains Using Geological, Geomor-Phological and Geophysical Methods, Western Hamissana Area, NE Sudan

This study aims at identifying target zones for groundwater exploration in basement terrains using geological, geomorphological, and geoelectrical methods. The study area is located on the northwestern side of the Red Sea Hills in the western Hamissana area. It is part of the Arabian Nubian Shield (ANS), which dates to the Pan-African Era. The study area is covered by Precambrian basement rocks which are overlain by alluvial deposits. The climate in the region is arid. As a result, severe water shortage is experienced. The geological and geomorphological investigations were carried out to locate potential sites for groundwater prospecting. On this basis, three categories of groundwater potential zones were delineated as good, moderate, or poor. The electrical resistivity method using vertical electrical sounding (VES) technique was used to determine the vertical geological profile of the study area. The sequence was revealed to consist of four zones: a high-resistance unsaturated zone, an intermediate-resistance water-bearing formation, a low-resistance wet weathered basement, and high-resistance fresh basement rock. Catchment boundaries were delineated using digital elevation models, and potential locations for surface and subsurface dams were proposed to improve the groundwater recharge.

GEOTECHNICAL INVESTIGATION OF THE PROPOSED IFE DAM SITE AT KAJOLA VILLAGE, ILE-IFE, SOUTHWESTERN NIGERIA

Geological and geophysical investigations were conducted to assess the competence and structural integrity of the foundation site of the proposed Ife-dam at Kajola Village, Ile-Ife, Southwestern Nigeria. Geological investigation along the two (2) proposed dam axes revealed that the overburden material is loose to dense with angular shearing resistance (ɸ) of 27o to 41o. The soils are predominantly elastic silts; cohesive with considerable strength and stability. Geophysical investigation involving the Schlumberger Vertical Electrical Sounding delineated four (4) lithologies namely: topsoil with resistivity of 69 – 558 Ωm and thickness between 1.5 and 4.0 m; weathered sandy layer with resistivity from 123 – 586 Ωm and thickness between 6.5 and 20.4 m; partially weathered/ fractured basement with resistivity from 60 – 220 Ωm and thickness between 6.5 and 14.0 m; and the fresh basement rock with resistivity from 1337 – 10683 Ωm. There are indications of fractures at a depth of 32 m beneath Axis B extending to Axis A at a depth of 35 m. The subsurface materials are suitable to host a dam. Axis B is more appropriate for the dam axis, although the fracture zone should be factored into the design of the dam to prevent water seepage.

GEO-ELECTRIC INVESTIGATION OF GROUNDWATER POTENTIAL IN LADERIN HOUSING ESTATE, ABEOKUTA, SOUTHWESTERN, NIGERIA

Vertical Electrical Sounding (VES) and 2D Electrical Resistivity Tomography (ERT), with Schlumberger and Wenner electrode array configurations respectively were employed to investigate the groundwater potential of Laderin Housing Estate located at Oke-mosan, Abeokuta, Ogun state, southwestern Nigeria. The area is underlain by the basement complex of the southwestern Nigeria. The research aimed at determining the aquifer/groundwater zone and characterizes the lithology of the study area. The geophysical survey involving nine VES and four profile of 2-D ERT lines with lengths varying from 100 m to 150 m were carried out. The field data from both the ERT and VES were processed and interpreted using RES2DINV and WINRESIST software respectively. Geometrical effects from the pseudo-section were removed and an image of true depth and true formation resistivity were produced. Three to four geo-electric layers were revealed in all, which are; topsoil, weathered layer, fractured and fresh basement rock. The result of 2 D inversion provide lithologic unit, weathering profile and geological structure favourable for groundwater potential. The results show that the basement rock was delineated with resistivity values that range between 701.3 Ωm and 9459.3 Ωm. The bedrock topography has a variable thickness of overburden between 3 m and above 16.4 m, which is fairly shallow. The geophysical survey show that VES 2, VES 3, VES 4, VES 5, and VES 6 are possible location for groundwater extraction. The difficult terrain, where thick overburden are located are also promising target for groundwater development.
 

Geoelectrical Investigations at Three Bridge Sites, North Nyala, Southern Darfour State, West-Sudan

Resistivity measurements were carried out to delineate the depth of the basement rocks (bedrock) and the lithology of the overlying sediments for the purpose of bridges construction route. The survey was conducted at three sites: Andro, Duma and Manwashi, north Nyala, Southern Darfur State, Western Sudan. These sites (Andro, Duma and Manwashi ) are located along Nyala _ El-Fashir road at a distance approximately of 15km, 42km and 75km from Nyala (respectively). The surface geology of the area is dominated by the basement complex rocks which are overlain by thin layer of superficial deposits
 The modeling of the VES data was done using IX1D software. The final results of the modeled and interpreted resistivity data are presented in the form of geoelectrical sections. These sections have shown a close agreement with the geological and hydrogeological conditions of the area. Three zones were identified in these sections, they are the top dry zone (<1m to >3m) representing the superficial deposits, the middle zone (Saturated zone) represents the groundwater aquifer. It varies in lithology from weathered and cracked basement rocks to the Alluvial deposits with a significant heterogeneous nature which varies from clayey, silty, sandy, pebbly and boulders layers. The bottom zone (Fresh basement rocks) represents the bedrock. It indicate an increase of hardness and compaction from Andro , Duma and Manshawi sites respectively. These findings can be used successfully for constructions the bridges of the three sites.

Geophysical and Contamination Assessment of Soil Spatial Variability for Sustainable Precision Agriculture in Omu-Aran Farm, Northcentral Nigeria

The Spatial and temporal variability of soil properties (fluid composition, structure and water content) and hydrogeological properties employed for sustainable precision agriculture can be obtained from geoelectrical resistivity methods. For sustainable precision agricultural practices, site-specific information is paramount, especially at the planting season. An integrated one-dimensional (1D) and two-dimensional (2D) electrical resistivity surveys have been adopted to characterize the subsoil parameters and delineate the aquifer unit of large farm area, especially in precision agricultural practices. Also, contamination assessment reveals the soil quality status of farmlands. This study aims to determine the site-specific soil parameters of a commercial farm in Omu-Aran, Northcentral, Nigeria. The subsoil features from the geoelectrical resistivity surveys indicate 3 to 4 distinctive lithology to a depth of 43.4 m into the subsurface of the farm. The ID (Vertical Electrical Sounding) and 2D resistivity inversion models results have revealed the heterogeneity nature of the topsoil also known as the stone zone comprising of reworked clayey soil and sandy gravelly soil, the weathered/saprolite zone (gravelly sandy/ sandy soil), the fractured basement and the fresh basement rock. Contamination factor (Cf), pollution load index (PLI) and Nemerow integrated pollution index (NIPI) were used to assess the contamination index on the farmland. Toxic elements such as arsenic, cadmium, chromium, cobalt, lead, manganese, nickel, and zinc have low to moderate contamination in the farm. The depth of investigation (≤ 3m) covers the upper root zone of significant crops grown in the area. The findings can assess soil contamination, delineate basement features, subsoil variability, soil profiling, and determine the subsoil hydrological properties.

Integrated magnetic and electrical resistivity investigation for assessment of the causes of road pavement failure along the Ife-Osogbo Highway, Southwestern Nigeria

This study combined magnetic and electrical resistivity investigations to assess the reasons for the persistent failure of road pavement along the Ife-Osogbo highway, southwestern Nigeria. Three traverses, each covering both stable and failed road segments, were established for ground magnetic, 2D dipole–dipole electrical resistivity imaging (ERI) and 1D Schlumberger vertical electrical sounding (VES) surveys. Data correction involving diurnal effect and offset were carried out on the magnetic data and the corrected data were presented as profiles and then modeled for 2D subsurface images. The VES and 2D ERI data were respectively modeled for layer geoelectric parameters and 2D resistivity images. The magnetic profiles and 2D magnetic subsurface models identified geologic structures (fault/fracture/contact zones) that are inimical to road pavement foundation beneath the investigated traverses. Subsurface sequences underlying the road segments are topsoil, lateritic layer, weathered layer, partly weathered/fractured basement and the fresh basement rock. Laterite, typical of competent subgrade for road pavement foundation, was generally observed beneath the stable segments while clayey weathered layer characterized the failed segments. From 2D resistivity images (upper 5 m), low resistivities (< 100 Ωm), typical of expansive clay, were observed partly beneath the stable but predominately beneath the failed road segments. Generally, it was observed that road segments founded on relatively high resistivity/lateritic layer were stable while the failed segments were associated with significantly thick and low resistivity weathered layer with thin/no lateritic topsoil cover. It was therefore concluded that the persistent road pavement failure along the Ife-Osogbo highway were caused by the clayey nature of the subsoil and the underlying geologic features.

Evaluation of groundwater potential of bedrock aquifers in Geological Sheet 223 Ilorin, Nigeria, using geo-electric sounding

Electrical resistivity data acquired in one hundred and ten (110) locations using vertical electrical sounding method of Schlumberger array have been used to study the hydrogeological properties and groundwater storage potential of bedrock aquifers in an area covered by Geological Sheet 223 Ilorin, Nigeria. The aim of the study was to identify productive aquifer zones for citing boreholes for community water supply. The data acquired were processed and interpreted using auxiliary curve matching and computer automation method to delineate the different geo-electric layers, their resistivities, thicknesses, and depths. Geo-electrical layers were interpreted to their equivalent geological layers using borehole lithological logs from the study area. Then, the hydraulic conductivity, transmissivity, fracture contrast, reflection coefficient were estimated and plotted in the form of 2D maps to describe the spatial variations of these parameters in the area. The results of the study revealed the presence of three to five geo-electric layers. The geo-electric layers, from top to the bottom, corresponds to the topsoil layer, lateritic layer, weathered rock layer, fractured rock layer, and the fresh basement rock. Lateritic and/or fractured rock layers were not delineated in some places. The weathered and fractured rock layers, where present, correspond to the aquifer units. The thickness of the fracture aquifer ranges from 0.6 to 33.6 m while the thickness of the weathered aquifer ranges from 1.4 to 49.3 m. The transmissivity, T , and hydraulic conductivity, K , range from 3 to 1200 m2/day and 1 to 48 m/day, respectively. The reflection coefficient and fracture contrast map showed the presence of water-bearing fractures and shared some similarities with T and K maps. A mathematical model for predicting groundwater potential, {text{GW}}_{text{P}} , of weathered aquifer in the basement complex terrain was proposed in this study. The consistencies between the overall groundwater potential map and aquifers parameters distributions maps suggest the appropriateness of the proposed mathematical model for predicting groundwater potential of weathered rock in the basement complex area of Nigeria. The western, northwestern, and central parts of the study area, having {text{GW}}_{text{P}} greater than 0.6 (60%), were recommended for groundwater development through boreholes drilled to a depth ranging between 75 and 100 m.

A Reconnainsances Study to Delianate Conductive Groundwater Zone Using Resistivity Sounding in Some Part of Kwara State North-Central, Nigeria

From the results, three to four electrostratigraphic layers with resistivity value ranging from 44 to 997 ohm/m and thickness ranging from 0.5 to 39.7 m were observed in the study area. The top loose rocks, the weathered conductive zone, the fractured basement rock and the fresh basement rock of older granite suite were encountered respectively. From this research, it can be deduce that, the thicker top soil and deeper weathered basement rock at the depth of 30 to 45 meters within this area produce a productive site for sitting future borehole. Insufficient groundwater supply in some places leading to scarcity is noticed in VES 10, VES 12 and VES 13. H, I, and A curve types are generally the most common in the area and are typical of basement complex area. Geographical Positioning System tool (model: GPSmap 76CSx), was used to locate the VES points. Fifteen VES points with electrode spacing [AB/2] of 100 meters separation around Ndanaku and environs were undertaken using Schlumberger configuration. IPI 2 Win [1990-2003] Geosoft resistivity sounding software was used to model the field curves from the measured data on the field. Groundwater in the area is regarded as poor due to localized nature of the aquifer and the study aimed at addressing this scarcity of water within the area by studying the conductive zone and knows the aquifer types through resistivity sounding techniques for future drilling.

Application of 3D electrical resistivity tomography to building foundation – A case study of Ahmadu Bello University

The recent failure of building foundations such as cracks, structural differential settlements and collapse has now become a great concern to geoscientists. A new site at Ahmadu Bello University, Nigeria, was investigated to explore the suitability of the subsurface material for the foundations of buildings, identify weak zones that may be prone to subsidence and the competence to support massive structures. This investigation was achieved with 3D electrical resistivity tomography (ERT). The data were obtained using Terrameter SAS 4000 and ES 464 electrode selector equipment and processed using the RES3DINV software. Dipole-dipole configuration at electrode spacing of 5 m was used to acquire the data along six profiles laid in the study area. The results in correlation with borehole data showed that the subsurface has a minimum of three geo-electric sections. It can be concluded that the competent layer with high resistivity values (746 to 1206 Ωm) is recommended for building or high rising building foundations due to its fresh basement rock. In the topsoil, clay formation should be avoided, this is because the clay materials are subject to differential settlement or flow under pressure.

2D geo-electrical imaging for groundwater exploration in Shika, along Zaria-Funtua Road north of Ahmadu Bello University main campus, Samaru, Zaria

A two dimensional (2D) geoelectrical tomography of Ahmadu Bello University Teaching Hospital Premises was carried out with the aim of identifying a suitable location for siting a borehole. This was sequel to the fact that a borehole drilled without proper geophysical investigation in the quarters for resident doctors did not produce water. State-of-the-art equipment was employed and 2D surveying proved a powerful geological mapping tool, for use in hydrogeological mapping including engineering and environmental applications. The 2D inversion results of the survey were correlated with the lithology information obtained from the boreholes in Jama’a village, and the hostels and the residential quarters of ABUTH. The stratigraphic structure of the study area is very complex and is a product of volcanic and magmatic activities of various ages. Based on the geo-electrical images obtained in the study area, three distinct layers were revealed, the overburden with an average thickness of about 16 m – 26 m. The overburden is immediately underlain by the weathered basement, 5 m – 14 m thick which consists of disintegrated schistose rock materials, sand and gravel. This layer has a relatively low resistivity due to the presence of water and clay, which reduces the permeability, so this layer is thus regarded as the aquifer. The fresh basement rock was encountered at a variable depth of between 21 m and &gt;30 m with resistivity 1223 Ωm up to 11918 Ωm. These results agree with the borehole logs. The complete set of borehole logs used in this research were obtained from the original hydro-geologic assessment report of the groundwater research department of the National Water Resources Institute (NWRI), Mando, Kaduna; Kaduna State, Nigeria.Keywords: Tomography, Inversion, Lithology, Geo-electrical, Aquifer, Borehole

Evaluation of a Weathered Rock Aquifer Using ERT Method in South Guangdong, China

In areas where weathering has hydrogeological significance, geophysical methods can assist to map the subsurface characteristics for groundwater occurrence. In this study, electrical resistivity tomography (ERT) survey in combination with joint profile method (JPM), magnetic method and borehole data was conducted to investigate the aquifer potential in strongly weathered volcanic rocks. The aim was to assess the geological units related to the water-bearing formation of aquifer systems in South Guangdong, China. The resistivities were measured along four profiles each with a total of 81 electrodes, a spread length of 400 m and an electrode spacing of 5 m insuring continuous coverage. The data from a borehole survey revealed three different layers i.e., highly weathered layer, partly weathered layer and fresh basement rock, whose respective thickness were integrated into ERT images to get more useful results about the real resistivity ranges of the these layers (i.e., 22 Ωm–345 Ωm for highly weathered layer, 324 Ωm–926 Ωm for partly weathered and 913 Ωm–2579 Ωm for fresh bedrock). The electrical resistivity imaging including the surface topography provides spatial variations in electrical properties of the weathered/unweathered layers since resistivity depends on the properties of a material rather than its thickness. ERT sections were integrated with JPM and magnetic method to delineate the main faults (F1, F2 and F3). ERT sections show a geometric relationship between different layered boundaries, particularly those of the aquifers with fresh basement and surface topographies. These layers comprise an overburden of 50 m thickness revealed by ERT sections. The results show that weathered and partly weathered layers between the topographic surface and bed rock yield maximum aquifer potential in the study area. ERT imaging method provides promising input to groundwater evaluation in the areas of weathered environment with complex geology.

Petrography and Geochemistry of Archaean Greywackes from Northern Part of the Dharwar-Shimoga Greenstone Belt, Western Dharwar Craton: Implications for Nature of Provenance

ABSTRACT Greywackes (Dharwar greywackes) are the most abundant rock types in the northern part of the Dharwar-Shimoga greenstone belt of the western Dharwar craton. They are distinctly immature rocks with poorly-sorted angular to sub-angular grains, comprising largely quartz, plagioclase feldspar and lithic fragments of volcanics (mafic+felsic), chert and quartzite, with subordinate biotite, K-feldspar and muscovite. They are characterized by almost uniform silica (59.78-67.96 wt%; av. 62.58), alkali (4.62-7.35 wt%; av. 5.41) contents, SiO2/Al2O3 (3.71-5.25) ratios, and compositionally are comparable to the andesite and dacite. As compared to Ranibennur greywackes, located about 100 km south of Dharwad in the Dharwar-Shimoga greenstone belt, the Dharwar greywackes have higher K2O, CaO, Zr, Y, ΣREE, Th/Sc, Zr/Cr, La/Sc and lower Sr, Cr, Ni, Sc, Cr/Th values. The chondrite normalized patterns of Dharwar greywackes are characterized by moderately fractionated REE patterns with moderate to high LREE enrichment, with almost flat HREE patterns and small negative Eu anomalies, suggesting felsic dominated source rocks in the provenance. The frame work grains comprising felsic and mafic volcanics, feldspars and quartz suggest a mixed source in the provenance. The moderate CIA values ranging between 57 and 73, indicate derivation of detritus from fresh basement rocks and from nearby volcanic sources.The mixing calculations suggest that the average REE pattern is closely matching with a provenance having 40% dacite, 30% granite, 20% basalt and 10% tonalite. These greywackes were deposited in a subduction related fore-arc basin than a continental margin basin. Their La/Sc ratios are high (av. 4.07) compared to the Ranibennur greywackes (1.79), suggesting that the greywackes of the northern part of the basin received detritus from a more evolved continental crust than the greywackes of the central part of the Dharwar-Shimoga basin.