SUBSOIL CHARACTERIZATION USING GEOELECTRICAL AND GEOTECHNICAL INVESTIGATIONS: IMPLICATIONS FOR FOUNDATION STUDIES

Electrical resistivity tomography (ERT) has been combined with geotechnical techniques such as cone penetrating tests, standard penetrating test and laboratory tests for detailed characterization of near-surface strata. This approach can be very helpful in conducting preliminary investigations towards a robust foundation design at a building construction site. Two ERT lines were conducted for 2D geoelectrical resistivity measurements using Wenner array configuration in combination with four cone penetrating data. Through the inversion of ERT data, two geoelectrical layers were interpreted to be loose silty sand and compacted clayey sand lithological units with the resistivity values ranging 50 – 280 Wm and 10 – 74 Wm respectively. A water saturated portion with resistivity values £ 3 Wm due to lagoon-water incursion was equally observed at the base of the second clayey sand layer in ERT line T2. The average cone penetrometer (CPT) value of about 110 kg/cm2 (11 MPa) with an average SPT ‘N’ value of 25 was measured between 6.75 – 30.0 m, indicating that the geomaterials within this depths range are of good geotechnical properties. Laboratory tests conducted on the representative soil samples at 3.75 m depth gives a moisture content (MC) of 66%. This is attributed to the clay contents within the soil samples. The Liquid Limit (WL), Plastic Limit (WP) and Plasticity Index (PI) tests of the soil samples gives 84%, 30% and 54% respectively. The results of the proposed approach, encompassing both geophysical and geotechnical methods has helped to steer the choice of the foundation for the investigated building towards a pile-type foundation rather than a shallow one. The pile foundation will cause the higher loadings to transmit the loads to a stable soil layer within the subsurface

The use of geological-based geophysical surveys for groundwater distribution in crystalline basement terrain, SW Nigeria

This research involves the subsurface geological characterization for groundwater potential assessment within the campus of the Polytechnic of Ibadan, southwestern Nigeria. The study is directed towards groundwater resources exploration, development and management in the campus. Five 2D resistivity imaging traverses were conducted using Wenner array in addition to five VES surveys using Schlumberger array that provide layering information and geoelectrical parameters. Three geologic layers delineated from the 2D resistivity inversion models include predominantly clayey sand/ sandy clay top soil (overburden), partly weathered or fractured basement and fresh basement. Their inverse model resistivity values ranges 6.68 – 98.6m , 68.0 – 929 m and 2252 m with bottom depths ranges 3.8 – 6.4 m and 6.4 – 10 m respectively. 1D model inversion from VES results also delineate three lithologies classifying both topsoil and some part of the partly weathered basement as overburden with resistivity and thickness range 483 – 1746.9 m , 1.1 – 1.8 m; partly weathered or fractured basement 60.3 – 93.5 m , 8.4 -12.9 m and fresh basement 984.6 – 2078.9 m . The saturated portion of the partly weathered or fractured basement at depth will favour groundwater exploration and development in this area, while the relatively shallow overburden thickness would serve as the protective layer and recharge for the fractures

The use of geological-based geophysical surveys for groundwater distribution in crystalline basement terrain, SW Nigeria

This research involves the subsurface geological characterization for groundwater potential assessment within the campus of the Polytechnic of Ibadan, southwestern Nigeria. The study is directed towards groundwater resources exploration, development and management in the campus. Five 2D resistivity imaging traverses were conducted using Wenner array in addition to five VES surveys using Schlumberger array that provide layering information and geoelectrical parameters. Three geologic layers delineated from the 2D resistivity inversion models include predominantly clayey sand/ sandy clay top soil (overburden), partly weathered or fractured basement and fresh basement. Their inverse model resistivity values ranges 6.68 – 98.6m , 68.0 – 929 m and 2252 m with bottom depths ranges 3.8 – 6.4 m and 6.4 – 10 m respectively. 1D model inversion from VES results also delineate three lithologies classifying both topsoil and some part of the partly weathered basement as overburden with resistivity and thickness range 483 – 1746.9 m , 1.1 – 1.8 m; partly weathered or fractured basement 60.3 – 93.5 m , 8.4 -12.9 m and fresh basement 984.6 – 2078.9 m . The saturated portion of the partly weathered or fractured basement at depth will favour groundwater exploration and development in this area, while the relatively shallow overburden thickness would serve as the protective layer and recharge for the fracture

Estimation of aquifer hydraulic parameters from surficial geophysical methods: a case study of Ota, Southwestern Nigeria

Geoelectrical resistivity surveys have been carried out using Schlumberger configuration within the Iyana Iyesi area of Ota, Ogun state. The aim of this research was to experimentally estimate the hydrogeophysical parameters of an aquifer (porosity, transmissivity, hydraulic conductivity and permeability) which have been completed successfully. Since drilling of boreholes specifically to compute the hydraulic parameters is relatively expensive, estimation of the parameters from vertical electrical soundings is considered a reliable alternative. The results showed that the study area has majorly low value of overburden materials serving as the protective capacity to the aquifers that are characteristically high in porosities and transmissivities. This low protective capacity denote the high vulnerability of the aquifer system to the influx of surface-based contaminants. The aquifer systems within the study area possess significantly high storativity property based on their high porosity and transmissivit

Prevalence and correlates of stroke among older adults in Ghana: Evidence from the Study on Global AGEing and adult health (SAGE)

This study examines the prevalence and correlates of stroke among older adults in Ghana. This cross-sectional study retrieved data from Wave 1 of the World Health Organization (WHO) Survey on Global Ageing and Adult Health (SAGE) conducted between 2007 and 2008. The sample, comprising 4,279 respondents aged 50 years and above, was analysed using descriptive statistics, cross tabulations and Chi-Square tests, and a multivariable binary logistic regression. Respondents ranged in age from 50 to 114 years, with a median age of 62 years. Stroke prevalence was 2.6%, with the correlates being marital status, level of education, employment status, and living with hypertension or diabetes. The results showed that being separated/divorced, having primary and secondary education, being unemployed and living with hypertension and diabetes, significantly increased the odds of stroke prevalence in this population. The results suggest that interventions to reduce stroke prevalence and impact must be developed alongside interventions for hypertension, diabetes and sociodemographic/economic factors such as marital status, level of education, and employment status

Non-communicable disease comorbidities in KwaZulu-Natal Province, South Africa

Background. The prevalence of chronic non-communicable disease (NCD) comorbidity in low- to middle-income countries is increasing, yet evidence on the pattern, prevalence, awareness and treatment of NCD comorbidity is inadequate.Objectives. To investigate the prevalence, awareness, treatment and control of comorbid hypertension and diabetes, and the underlying risk factors in Mpumza, KwaZulu-Natal Province, South Africa (SA).Methods. Data were gathered by the SA Human Sciences Research Council from 587 participants in KwaZulu-Natal in 2015. Percentages were used to describe all the variables. Cross-tabulations and χ2 tests were used to describe variations in the prevalences of hypertension, diabetes and comorbidities according to sociodemographic and socioeconomic variables and lifestyle risk factors.Results. Approximately a third of the participants had hypertension (32%) and 9% had diabetes. The prevalence of comorbid hypertension and diabetes was 6%, and this was significantly higher among women, the aged, the obese, and the formerly married compared with their counterparts. Comorbidity awareness was high (86%). Although most of the participants with comorbidities were being treated with lifestyle changes, insulin and antihypertensive medication (74%), control of comorbidities was low (13%).Conclusions. The study reported a higher burden of comorbid hypertension and diabetes among vulnerable populations in Mpumza, SA, particularly women, the obese, and those with a low level of education. In addition, control of comorbidities was low. Developing appropriate interventions to improve control of comorbidities can reduce the risk of macrovascular and microvascular diseases in this population

Comparison of Conventional Schlumberger and Modified Schlumberger Arrays in Estimating Aquifer Parameters in A Typical Basement Complex, Southwestern Nigeria

This study compared the interpretation results of the Vertical Electrical Sounding (VES) data acquired using the conventional Schlumberger and modified Schlumberger arrays with a view to assessing the effectiveness of the modified Schlumberger arrays of VES as alternatives to the conventional Schlumberger array at sites with space constraint during geophysical exploration. A total of thirty (30) VES data for both conventional Schlumberger and modified Schlumberger arrays were collected across different rock units within Federal University Oye-Ekiti campus and Irare estate in Oye-Ekiti metropolis, south-western Nigeria, with electrode spacing

Assessing the suitable electrical resistivity arrays for characterization of basement aquifers using numerical modeling

Numerical modeling analysis was used to assess the suitable electrical resistivity arrays for the characterization of geological structures, including dyke, horst, graben, sub-vertical, and vertical structures. These geological structures usually make up the aquifers interested in the hydrogeological evaluation of crystalline basement terrains. Six electrode configurations, including Wenner alpha (α), Wenner beta (β), Wenner gamma (γ), Schlumberger array, dipole-dipole array, and pole-dipole array, were used to assess the geological structures for groundwater exploration. The synthetic models of the geological structures were generated using RES2DMOD code, and 5% noise was added to all the models. The generated models were inverted using the RES2DINV code. The results show that the most suitable arrays for dyke and graben structures are Wenner alpha, while Wenner beta is the most suitable for the horst structure. The Schlumberger array was the best for both sub-vertical and vertical structures. This study has demonstrated the efficacy of numerical modeling in assessing the best resistivity arrays for 2D electrical resistivity imaging for groundwater exploration prior to geophysical field investigation

Geoengineering site characterization for foundation integrity assessment

Inefficient near-surface characterizations prior to building construction have largely contributed to the incessant building failures in the form of structural defects and building collapses recently occurring in southern parts of Nigeria. Combined geophysical and geotechnical investigations have been used to select suitable foundation type and depth at a building construction site in part of the Lagos Island, Nigeria. Three geoelectrical resistivity survey profiles of length 150 m each were conducted using minimum and maximum electrode spacing of 5.0 m and 45.0 m, respectively. Boring, in-situ geomaterials samplings, cone penetrating tests, standard penetrometer tests and laboratory tests were among the geotechnical investigations carried out in accordance with the British standard code of practice. The geoelectrical resistivity imaging results provide the lateral and spatial spread of the geoelectrical units stratification within the study area, their clay and water contents. The results of the laboratory and geotechnical tests also reveal the subsoils lithologic units, their compressibility and shear strengths. A deeper piletype foundation on a more competent stable subsoil stratum at the depth greater than 13 m is recommended for the proposed buildings in the study area so as to effectively transmit their loads

Understanding the interrelationship between electrical anisotropy and groundwater yield in a typical Basement Complex area

The rocks in the Basement Complexof southwestern Nigeria exhibit electrical anisotropy as a result of their heterogeneous nature caused by weathering, near-surface effects or presence of fractures. It is known that groundwater yield (Y) in a typical Basement Complex aquifers is related to its coefficient of anisotropy (). Therefore, it is essential to study the correlation between Y and in the basement complex. Ten (10) vertical electrical sounding (VES) points using Schlumberger array were studied in areas underlain by migmatite gneiss and quartzite rocks. The current electrode spacing (AB/2) varies from 1 m to a maximum spread length of 100 m. The quantitative interpretation of VES curves was done by using partial curve matching and computer assisted program called WinResist version 1.0 software. Dar Zarrouk parameters were estimated from the interpreted VES curves and thus coefficient of anisotropy () was calculated from these parameters. Data on the groundwater yield at the VES points were also obtained. The results show that as increases, Y also increases with coefficient of correlation (R2) of 0.86 and 0.79 for migmatite gneiss and quartzite rocks respectively. To further investigate the relationship between Y and, a regression analysis was performed. The regression analysis that was performed on the dataset shows that contributes significantly to the regression models of the two rocks. The relationship between Y and reveals that groundwater yield could be predicted from the values of in a given locality