Schlumberger Vertical Electrical Sounding Research Articles

Geophysical and geoenvironmental engineering assessment of contaminated workstation soils in a metamorphic environment

This study aims to employ the electrical method, multi-pollution indices, and statistical optimization to establish a common ground for the utilization of contaminated soil as construction material and for agricultural purposes. Two samples each were taken at a depth of 0.5 m and 1.0 m from the eatery, auto-mechanic, car wash, and transformer workstations and at a control site in Akungba-Akoko, southwestern Nigeria. The concentrations of the following geochemical parameters were analyzed: Cr, Pb, Zn, Cd, Mn, and Cu. The resistivity distribution of the workstations’ subsurface layers was determined using Schlumberger vertical electrical sounding (VES). The generated geoelectrical sections revealed four geoelectric layers (topsoil, weathered layer, partially weathered/fracture bedrock, and bedrock) with two curve types: HA (50%) and AA (50%) across the workstations. The topsoil resistivity values (65–184 Ωm) from the VES results suggest moderately rich organic matter and averagely very fine-grained sand. The concentrations of the heavy metals in all the soil samples are within the maximum allowable concentration as stipulated by the National Environmental Standards and Regulations Enforcement Agency in the soil and are suitable for farm activities. Similarly, the geotechnical tests of the Atterberg limit, grain size analysis, compaction, and CBR revealed that all the soil samples met the criteria of a good pavement design but with poor landfill material. Pearson's correlation coefficient revealed that a strong relationship between Igeo\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${I}_{geo}$$\\end{document}-PLI, Igeo\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${I}_{geo}$$\\end{document}-RI, PLI-RI, TSR-Fines, MDD-CBR, LL-MDD, and LL-CBR exists among the multi-pollution indices, the geotechnical properties of soil, and the resistivity distribution of the topsoil. This suggests similar levels of heavy metal pollution and a common source of anthropogenic activities throughout the four workshops and provides the link between geotechnical properties and resistivity distribution for future soil management strategies. The exposure of children and adults to multiple heavy metals through inhalation at the four workstations shows no significant non-cancer or cancer risks.

Soil–water contamination assessment due to dumpsite-impacted leachates in a metamorphic environment

Environmental contamination is a complex issue that significantly impacts human health and ecological systems, especially in developing countries like Nigeria. This study explores the interplay between surface-subsurface soil-rock resistivity and subsurface geotechnical properties, along with multiple soil-water pollution indices at and around the Old Owo-Ikare road (OOIR) dumpsite in southwestern Nigeria. Water samples from five wells and one stream were collected and analyzed, alongside twelve soil samples from four trial pits at varied depths for geoenvironmental assessment. Analyzed hydrogeochemical parameters include Na, Ca, Mg, K, Cr, Pb, Zn, Ni, Mn, Fe, and cations (NO, SO4, Cl) in the water samples. Nine dipole-dipole electrical resistivity tomography (ERT) profiles and six Schlumberger vertical electrical sounding (VES) points were used to determine surface–subsurface resistivity distribution. Water analysis results showed elevated levels of K, Ni, Cr, and Pb concentrations. Geotechnical tests indicated that most dumpsite soil meets good landfill material criteria with low permeability (5.92×10−6 to 1.49×10−4cm/s). ERT and VES inverted models revealed four lithologic layers with two main curve types (HA and QA). Elevated heavy metal levels in the dumpsite soil and inverted resistivity models suggested leachate contamination in the topsoil and weathered bedrock units. Despite relatively lower heavy metal concentrations compared to other Nigerian and Ghanaian dumpsites, multi-pollution indices indicated significant contamination in both water and soil samples, posing moderate to very high environmental risks based on World Health Organisation standards. Additionally, human health risk assessment suggested a risk of cancer and non-cancer-related diseases from prolonged well water consumption. Therefore, ongoing monitoring and remediation efforts are essential to forestall imminent pollution in uncovered areas.

The use of Electrical Resistivity Methods to Investigate Water Table Potentials of Awka South Local Government Area, Anambra State, Nigeria

Purpose: Geophysical exploration for water table characteristics were carried out in six (6) communities of Njikoka and environs through which water table depth, depth below the water table, thickness of the saturated zone, depth with reference to mean sea level (MSL) and types of aquifer were deduced. The proven geoelectric sections of the study area based on resisitivity from the subsurface and electrical log which confirmed that depth to water table of Njikoka and environs could range from 15 m – 100 m. Depth below the water table in the study area ranged 40 m (around Nimo, Enugu Agidi) to 200 m (Ifitedunu, Ukpo) while the thicknesses of the saturated zones (aquifers) varies from 25 m to 160 m within the respective communities. Depths to Mean Sea Level were delineated to range from – 20 m to – 198 m as obtained from the difference in the water table depths and the heights above sea level which is the elevations.
 Methodology: Subsurface geophysical exploration was employed in the research of groundwater availability of Njikoka and environs. Schlumberger Vertical Electrical Sounding which is the subsurface geophysical method was carried out only on two locations in each of the communities. The geophysical investigation was made with Earth Resistivity equipment
 Findings: From the revealed results the study area is dominated with low land topography and prominently composed of unconfined with less cases of confined aquifer as a result of the geological settings of the study area.

Geohydraulic characteristics and groundwater vulnerability assessment of tropically weathered and fractured gneissic aquifers using combined georesistivity and geostatistical methods

Sustainable groundwater yield in aquifers depends on the protective capacity of the subsurface lithologies and conduit systems. Electrical resistivity tomography (ERT) and its Schlumberger vertical electrical sounding (VES) technique were employed to assess the groundwater yield of aquifer units and their vulnerability to contaminants in Araromi (Akungba-Akoko), southwestern Nigeria. Geohydraulic parameters: aquifer resistivity (\rho0), hydraulic conductivity (K), transmissivity (T), permeability (\Psi), hydraulic resistance (KR), and longitudinal conductance (S) were also evaluated. In addition, regression analysis was utilized to establish the empirical relationships between the K and other geohydraulic parameters, with their percentage contributions to posing vulnerability risk. The georesistivity results revealed four distinct layers: topsoil, weathered layer, partially weathered/fractured bedrock unit, and fresh bedrock. The K model regression-assisted analysis showed that the \rho, T, \Psi, and S contributed about 97.8%, 14%, 99.9%, and 11.5%, respectively, to the estimated aquifers’ K values for the study area. Except for T and S, the regression results had moderate to strong positive correlations with K; hence, this illuminates the essentiality of K in assessing groundwater potential and vulnerability. The aquifer units have low to moderate groundwater yield based on T values (1.67-17.57 m/day) caused by the generally thin overburden (<4 m). However, the deep-weathered and fractured aquifer units with depths ranging from 39-55 m could supply high groundwater yield for sustainable abstraction. The estimated S values (0.0226-0.1926 mhos) for aquifer protective capacity ratings rated the aquifer units in the area as poor to weak. Based on the estimated low logarithm of KR (log KR) values of 0.79-2.25 years, these aquifers have extremely high to moderate aquifer vulnerability index. As a result, prospective wells/boreholes in the study area and settings with similar geohydraulic and vulnerability characteristics should be developed adequately to prevent the infiltration of surface contaminants for potable groundwater abstraction.

Exploration of Aquifer Levels in Abraka, Obiaruku and Umutu Communities in Delta State, Nigeria

The Schlumberger vertical electrical sounding method was used to detect aquifer levels in Abraka, Obiaruku and Umutu communities in Delta State respectively. The study recorded the aquifer level in Obiaruku to be between 26m to 34m. In Abraka the aquifer level lied between 20m to about 30m while in Umutu, it was between 50m to 100m. Borehole data showed that portable drinking water lies between 20m to 100m and could easily be assessed in these areas.

Subsurface Investigation for Road Construction Using Electrical Resistivity Method along Oloko road, Apatapiti, Akure, Ondo State, Nigeria

Abstract Evaluation of the shallow geologic materials in terms of types, nature, and bedrock structure as possible causes of pavement failure was carried out along Oloko road Apatatpiti, Akure, Nigeria, using Schlumberger vertical electrical sounding and 2-D imaging dipole-dipole techniques. Three lithological layers, namely thin top soil, weathered layer and weathered basement, were revealed by the 2-D resistivity structure. Vertical electrical soundings were made at locations with a very low resistive medium typical of linear features such as fractures/faults at some distances on the 2-D resistivity structure. Four geologic layers, namely the top soil, clay/sandy clay, fractured basement, weathered/fresh basement, were identified by the geoelectric section. The geoelectric section and the 2-D resistivity structure revealed that the upper 0-6m, which constitutes the subgrade, has a low resistivity (36 Ωm to 108 Ωm) characterised to be clayey materials and suggestive of weak zones that might impair the stability of the road. A relatively shallow depth, ranging from 3.7 m to 4.29 m, was the depth to the water table of the four wells close to the road. Therefore, the possible causes of pavement failure are the thick and low resistive layer, the near-surface linear features suspected to be fractures/faults, and the water table’s shallow depth.

Combined geospatial, geophysical and hydrochemical studies on coastal aquifer at Muttom–Mandaikadu area, Tamilnadu, India

A study was conducted in the Muttom-Mandaikadu coastal region, which is among the profitable coastal sectors in Tamil Nadu, to find the groundwater potential as well as its quality by an integrated geospatial, geophysical and geochemical approach. The GIS-based weighted overlay analysis was used to merge five thematic layers to create the groundwater potential zone map. The geophysical resistivity survey was performed in the study area at 26 stations by applying Schlumberger vertical electrical sounding technique. The observed data were inverted to develop a subsurface lithology model and its electrical properties using one-dimensional software AGI Earth Imager. The combined vertical electrical sounding result and remote sensing thematic maps have exposed the potential zone of groundwater in the study area. From the inferred results, it was observed that 20.8% of the area has ample groundwater potential and 7.7% of the area has scanty groundwater potential. The saltwater intrusion zone had been predicted by validating aquifer resistivity with Dar-Zarrouck (D-Z) parameter. From the geophysical and geochemical interpreted results, it was found that aquifers in 34.6% of the study area are vulnerable to saline contamination. The 4-D model with integrated groundwater quantity and quality suggests that the study area's Western part falls under excellent-to-good groundwater potential zone and excellent water quality.

Groundwater Recharge Planning Using Field Survey for Talupula Mandal in Anantapur District, Andhra Pradesh, India

Groundwater is essential to the sustainability of India’s environment, economy, and living conditions because it isn’t just the primary source of domestic supply of water in rural areas, but it is also the major and most productive origin of the water. The increased demand for groundwater as a result of reduced rainfall has put a strain on groundwater resources in areas where groundwater is the primary supply of water. The main aim of this study is to identify and explore the groundwater potential zones in Talupula Mandal of 280.3 km2 in Ananthapur district in Andhra Pradesh, India with semi-arid climatic conditions. Based on the field survey approach, groundwater availability is found out in the villages. Schlumberger Vertical Electrical Sounding (VES) survey technique was used to discover the resistivity and thickness of the unmistakable layers. It was carried out in 18 randomly selected sites where groundwater plays an important role in agricultural and domestic use. The thickness and resistivity of first- and second-layer crack sites of the various layers were separated from ground data using IPI2WIN programming. Using software, graphs were plotted and groundwater potential zones were identified for recharging the groundwater. Based on the results, different models of recharge structures for the study area are identified and recommended. Hence the management of groundwater paves the way for sustainable groundwater levels.

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.

AQUIFER VULNERABILITY EVALUATION IN SOUTHWESTERN NIGERIA FROM AHP-GODT MODEL USING GEO-ELECTRICAL DERIVED PARAMETERS

<em>The study aimed to determine the exposure levels of the subsurface aquiferous layers, owing to the alarming rate of contamination of the groundwater within 8.150 <sup>0</sup>N - 8.156 <sup>0</sup>N and 4.244 <sup>0</sup>E - 4.248 <sup>0</sup>E. Thus, aquifers' overlying layers, resistivity, and thickness anomalies were determined to generate an aquifer vulnerability map. A multi-criteria decision method of estimated Groundwater confinement, Overlying strata, Depth to Aquifer, and Topography index approach was implemented. Schlumberger's Vertical Electrical Sounding technique was implemented to acquire 30 Vertical Electrical Sounding points under a maximum half-current electrode separation (AB/2) of 65 m. IP2Win geophysical software packages were used to analyze the varying layer resistivity, depth, thickness, and also the sounding curves of the study area. The 2D model revealed a maximum of four geo-electric layers. The layers' resistivity and thickness ranges are clayey silt topsoil (52.5-1104 Ωm; 0.5-9.59 m), weathered layer (10.3-804 Ωm; 0.6-12.1 m), fractured basement (5.5-50832 Ωm; 6.7-18.1 m) and fresh basement (8.3-27348 Ωm; infinity m). On the Groundwater Overlying Strata Depth to Aquifer and Topography model scale, the area is generally characterized by the moderate vulnerability. Implying here is that aquifers have a moderate protective capacity in which the overlying strata above the aquifer are mostly impermeable layers (clay and silt) of high thickness and low porosity.</em>

Subsurface Investigation of Basement Structures Using Electrical Resistivity Methods at Zainawa Village Kano, Nigeria

Electrical Resistivity Methods involving Schlumberger Vertical Electrical Sounding (VES) and Wenner Electrical Profiling (EP) were carried out to map the Geological features of the earth subsurface in Zainawa Area of Kano State, Nigeria. Five profiles were established; consist of six (6) VES points at each profile. GEOPULSE resistivity meter (SAS 300) was used for the data acquisition. The field data obtained have been analyzed using computer software (IPI2win) which gives an automatic interpretation of the apparent resistivity. A maximum of three geoelectric subsurface layers were delineated from the VES master curves. The geoelectric section beneath the study area was composed of top soil (clayey-sandy and sandy-lateritic), weathered layer, partly weathered (fractured basement) and fresh basement. The resistivity value for the topsoil layer varies from 20 Ωm to 600 Ωm with thickness ranging from 0.5 to 7.2 m. The weathered basement has resistivity values ranging from 15 Ωm to 593 Ωm and thickness of between 2.75 to 33.04 m. The fractured basement has resistivity values ranging from 201 Ωm to 835 Ωm and thickness of between 11 to 20.4 m. The fresh basement (bedrock) has resistivity values ranging from 1161 Ωm to 3115 Ωm with infinite depth. The depth to basement map was produced to give a good picture of the basement topography within the study area. The depth to basement ranges from 11 m around VES 01 to 85 m around VES 25 m. The map also reveals linear structures (VES 05, 21, 22 and VES 23) which trends in the NE-SW direction. These structures suggest a basement depression at these points. However, the depth from the topsoil to the bedrock surface varies between 2.5 to 37.75 m.

Hydrochemical appraisal of groundwater quality for drinking and irrigation: a case study in parts of southwest coast of Tamil Nadu, India

The quality of groundwater standards in Muttom–Mandaikkadu coastal stretch is the focus of the present study, whose coastal aquifers are particularly at risk due to intrusion of marine water. Thirty groundwater samples were scrutinized for the assessment of physical and chemical parameters during January and June. Hydrochemical characteristics were spatially depicted to understand the spatial variations such as (pH, EC, TDS, Na+, K+, Ca2+ and Mg2+, SO42−, HCO3−, and Cl−). Drinking water quality index based on those 11 parameters and irrigation water quality index based on EC, Na%, sodium adsorption ratio and permeability index was used to assess the water quality for drinking and irrigation, respectively. These results demonstrate that dominant hydrochemical facies for groundwater in both months are Na-K-Cl-SO4 type and Ca-Mg-Cl-SO4 type. The USSL diagram endorses that most of the water samples belong to low-medium salinity with low sodium hazards. Cl−/HCO3− ratio indicates that the majority of the samples show low to moderate seawater intrusion in the study area. Additionally, six vertical electrical sounding measuring points (Schlumberger array) were carried out in order to determine the number of the underlying layers, aquifer depths and their thicknesses as well as its influence by the marine water. The geophysical self-potential measurements suggest that the groundwater in the Manavalakurichi area is prone to contamination by seawater intrusion, confirmed by the use of Schlumberger vertical electrical sounding. For better understanding, the subsurface layers were shown in a 2D model using the constructed geoelectrical cross section.

Combined geophysical and geotechnical investigation of pavement failure for sustainable construction of Owo-Ikare highway, Southwestern Nigeria

ABSTRACT Very low frequency electromagnetic (VLF-EM) and electrical resistivity methods involving 54 Schlumberger Vertical Electrical Sounding (VES) and 2-D geoelectrical resistivity imaging using dipole-dipole array were utilised along unstable (US) and stable sections (SS) of Owo-Ikare highway to establish causes of its persistent failure. Engineering evaluation of eighteen soil samples from test pits excavated on selected US and SS were investigated. VLF-EM models, geoelectric sections and 2-D resistivity structures revealed existence of conductive subsurface structures, suspected weak zones beneath the US. The road pavement is constructed on poor clayey subgrade with low resistivity values (<100 Ohm-m) which precipitate instability of the highway. Subgrade soils below US have poor geotechnical properties characterized by high moisture content, liquid limit (43.6–63.8% and 20.1–25.2%), plasticity index (13.4–34.4% and 6.5–8.3%), percentage fines (40–67% and 28–30%), A-7-5 to A-7-6 clayey soils, high linear shrinkage (>10%), low compacted density, low CBR, volume changes (Mv) and impervious soils against those of SS. . Thus, deep-weathering, fractured bedrock, uneven bedrock topography with subsurface structures, water-saturated clayey subgrade and unsuitability of the soils for subgrade and subbase road construction are responsible for instability of the road. Replacement of soil beneath the unstable sections and effective drainage enhances its stability.

Aquifer Vulnerability: Its Protection and Management—A Case Study in Pangkalpinang City, Indonesia

Increased anthropogenic activity in urban areas has exacerbated the vulnerability of groundwater resources. The AVI, GOD, SINTACS, and DRASTIC methods were used to analyze groundwater vulnerability in Pangkalpinang City. Schlumberger vertical electrical sounding was used to determine the lithology and aquifer configuration in the study area. There are three vulnerability index areas in the city of Pangkalpinang. Low levels of aquifer vulnerability were generally found in the southeastern and northwestern parts of the study area, whereas high levels of aquifer vulnerability were discovered in the northern and southern parts of the study area. Areas with low aquifer vulnerability levels generally have low hydraulic conductivity values on the protective layer. In these areas, groundwater extraction is possible with a reasonable extraction pattern. Industrial areas can also be built by considering environmental aspects. In an area with high-level aquifer vulnerability, groundwater pollution must be considerably managed. The areas should not be designated for industrial areas and excess groundwater extraction.

Land satellite imagery and integrated geophysical investigations of highway pavement instability in southwestern Nigeria

The high global numbers of road accidents due to bad roads and the failure of other engineering structures have necessitated this study, particularly as road transport accounts for a higher percentage of cargo movement in African countries. The geophysical investigation was carried out on six failed and two stable sections along the Ibadan-Iwo-Osogbo highway to examine the geological factors responsible for highway failure in the area. A Landsat ETM+ (Enhanced Thematic Mapper Plus) imagery of the study area and its environs was acquired and processed for lineaments analyses. Magnetic, Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity methods involving Schlumberger Vertical Electrical Sounding (VES) and 2-D imaging using a dipole- dipole array were utilized. Lineaments were identified across failed localities. Lateral magnetic variations in the near-surface geological materials characterized the study area. The 2-D VLF-EM models generated showed conductive zones corresponding to fractured zones of conductive clay materials within the basement rocks. Subgrade soils below the highway pavement along the failed sections are typical of incompetent clayey and sandy clay/clayey sand formations with resistivity values between 20–475 Ω∙m. In comparison, the subgrade soil beneath the stable sections has moderate to high resistivity values of 196–616 Ω∙m. 2-D resistivity structures across the failed segments identified low resistivity water-absorbing clay and lithological contacts. Water absorbing, clay enriched subgrade soils and the identified near-surface linear conductive features are the major geologic factors, and poor drainage network resulted in the highway failure. Remote sensing and geophysical investigations of the geological sequence and structures underlying the highway should be carried out before construction to effectively complement the routine geotechnical studies to ensure the sustainability of road nfrastructure.

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.

Contribution of geophysical methods in characterizing the structure of El Fahs plain: Hydrogeological implications

The El Fahs plain aquifer belongs to Tunisian Northern Atlas and it is particularly important due to its exploitation, well yields and the water's chemical quality. In recent years, the increasing exploitation is becoming unsustainable and this warrants studies and policies to better manage the groundwater resources in the El Fahs plain. Therefore, it is crucial to understand the subsurface structure and to determine the zones that are favourable for the exploitation of potential units. For these purposes, a geophysical study by gravity and electrical resistivity methods has been conducted.The gravity method consisted in 1365 gravity data points collected from uniformly-distributed stations. The Bouguer anomaly map of El Fahs plain and its surrounding areas provided information about the subsurface density variation and showed positive anomalies indicating raised zones and negative anomalies characterizing the depression zones. Quantitative treatment applied to Bouguer anomaly map highlighted new deep structures with details on their depths (up to 2800 m) and dips. These results demonstrate that the plain corresponds to a collapsed area limited by three fault systems E-W, NW-SE and N–S. Some of these faults are conform to the existing ones. However, a new N–S fault system is highlighted, which produced a new structural map.A study by vertical electrical sounding (VES) survey was conducted in order to provide details on El Fahs plain. It consisted of 114 Schlumberger VES with lengths of current line AB ranging from 400 to 600 m. Interpretation results of the VES shows that El Fahs plain is covered by a very heterogeneous and thick Quaternary filling deposits (48 m by place). The Mio-Pliocene deposits have a thickness that occasionally exceeds 190 m, and it is composed of conductive (<15 Ω m) and resistant (>16 Ω m) units. The underlying Upper Cretaceous is composed of conductive (<17 Ω m) and resistant (>20 Ω m) units.From a hydrogeology point of view, the gravity results show that the groundwater flow is strongly influenced by the basin morphostructure and the existing faults in the area. Furthermore, the VES results reveal that three normal faults are responsible for collapsing the central part of the plain and favouring groundwater flow in this direction.

Integration of geophysically derived parameters in characterization of foundation integrity zones: An AHP approach

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.

Investigation of groundwater potential zones in NandiAru Sub Basin, Tamilnadu, India—an integrated geophysical and geoinformatics approach

Groundwater plays a vital role in the development of human and agricultural activities in India. Assessing the groundwater potential zone is extremely important for the protection of water quality and the groundwater management system. In this view, the study is carried out to investigate the groundwater potential zones for the assessment of groundwater availability in NandiAru sub-basin, Tamilnadu, India, by using a multidisciplinary database. Integration of geophysical techniques and geoinformatics can provide a suitable platform for convergence of multi-disciplinary data from different sources of planning. Using geophysical techniques 27 Schlumberger vertical electrical sounding (VES) survey was carried out up to a depth of 150 m in the whole study area. The field data were interpreted by using IPI2WIN software to find out the earth subsurface thickness and resistivity of different layers. The spatial distributions of thematic layers were prepared from geophysical resistivity survey data and these integrated over geology, geomorphology, and lineament density by using Arc GIS 9.3. These thematic layers were used as parameters in analytic hierarchy process (AHP) method to derive the priority values of all thematic layers. The groundwater potential map has been prepared based on the priority values of each thematic features and the potential of groundwater classified as high, moderate, and low zones.

The basement and tectonism of the river Jama’are floodplain: deduction from DC resistivity data

The analysis of DC resistivity data of part of the River Jama’are Floodplain, Northeastern Nigeria was carried out with a view to mapping the basement and the subsurface structures. One hundred and six Schlumberger Vertical Electrical Sounding (VES) stations located at the corners of a 225 x 225m square grid network were occupied. The interelectrode spacing (AB/2) was varied from 1-225m. Results identified four subsurface geologic layers; topsoil, alluvial sand, Chad Formation/weathered column and basement bedrock as undulating and basal unit at different depths. Four major parallel basement depressions suspected to be regional faults striking approximately NW-SE were delineated. This trend correlated with the general trend of the regional structures in the Chad Basin. The isopach maps of the topsoil and alluvial sand mirrored a more recent NE-SW trend that correlated with the Tibesti-Cameroon trough. However, this recent induced tectonics was adjudged significant to hydrogeology in the area. KEYWORDS : Resistivity, floodplain, basement, sounding, tectonics, hydrogeology