Geophysical and Geotechnical Characterization of Newly Constructed Abadina-Ajibode Road, University of Ibadan, Ibadan (original) (raw)
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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 m Ω and 10 – 74 m Ω respectively. A water-saturated portion with resistivity values ≤ ≤ ≤ ≤ 3 m Ω 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/cm 2 (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 Subsoil Characterization Using Geoelectrical and Geotechnical Investigations: Implications For Foundation Studies http://www.iaeme.com/IJCIET/index.asp 303 editor@iaeme.com shallow one. The pile foundation will cause the higher loadings to transmit the loads to a stable soil layer within the subsurface.
Subsoil evaluation within a proposes site for civil engineering structure by using geoelectrical and geotechnical methods of investigation carry out. The study aims to provide information on the stratigraphy, thickness, nature, and competence of the subsoil. Eighteen (18) Vertical Electrical Sounding (VES) stations using Schlumberger configuration occupy and complement with geotechnical analysis of eighteen (18) soil samples collect at all the VES points at depth not exceeding 1m within the study area. The VES interpretations delineate four main geoelectric sequences which comprise of the top soil, mixture of clay and sand, gravely sand and sandy gravel. The top soils are generally thin (< 2 m) and majorly composes of clayey silt/ silty clay /sandy clay/ clayey sand/ fill materials. The layer resistivity ranges from 0.75-19.6 Ωm for topsoil, 1.71-6.7 Ωm for clay and sand mixture, 0.01 – 2.69 Ωm for saturated gravelly sand layer and 4.23-4.61 Ωm for saturated sandy gravel layer. Low resistivity values at the study area are due to moisture and clay content within deposits at the study area. The geotechnical results show that the soil is relatively high clay content, intermediate to high moisture content and high plasticity. It concludes from the combined results above, that the topsoil is generally geotechnically less competence soil and may not serve as a good foundation material, therefore shallow foundation may not be feasible in studied area and, for engineering structure to be erected on such soil there is need for soil improvement or pilling to the sand layer.
Incessant building collapse and foundation failures in Nigeria have continued unabated in recent years, causing loss of lives and properties worth hundreds of thousands of US dollars. This research in Gioni estate Lakowe, Lekki-Epe, Lagos, Nigeria is concerned with an integrated characterization of near-subsurface geomaterials using geoelectrical resistivity tomography and geotechnical techniques as part of the preliminary investigations for foundations studies and other building construction projects. Four traverses of the geoelectrical resistivity measurements using Wenner array configuration were conducted, and cone penetrating data were equally obtained along the same traverse. A borehole data point was equally acquired for ground thruthing. Based on their geoelectrical properties, three lithologies including loose sand, compacted clayey sand and clay/peat units were delineated with apparent resistivity values ranging 50 – 260 Ωm, 20 – 72.2 Ωm and ≤ 27.5 Ωm respectively. Average Cone penetrometer (CPT) value was about 110 kg/cm2 with an average SPT ‘N’ value of 25, indicating that the soil material is of good geotechnical properties. Laboratory tests conducted on the representative soil specimen at 3.75 m depth revealed moisture content (MC) of 66% which can be attributed to the clay contents. The Liquid Limit (WL), Plastic Limit (WP) and Plasticity Index (PI) tests results gives 84%, 30% and 54% respectively. The choice of deep seated foundation such as pile foundation is considered a better alternative to shallow foundation for proposed buildings in the study area where higher loadings are anticipated to transmit the loads to a stable soil layer.
J Geol Geophys 7: 453, 2018
An integrated geophysical and geotechnical investigation for a proposed building foundation of an industrial plant layout was carried out to determine the competency of the subsoil as foundation materials. Electrical Resistivity Imaging (ERI) and soil analyses techniques were adopted. Two traverses of four Vertical Electrical Sounding (VES) points were carried out and 8 Boreholes for Standard Penetration Test (SPT) were drilled. In addition soil samples were taken at 1.5 m and 10 m depths and subjected to various laboratory analyses. Three geoelectric layers were delineated from VES including topsoil, saturated sandy clay soil and limestone. The SPT N value indicates that the relative density of the soils is medium dense to very dense while the result of the geotechnical analyses shows that maximum dry density of the soils range from 1680-1900 kg/m3 and 1600-1850 kg/m3 respectively at 1.5 m and 10 m while the optimum moisture content range from 14-19% and 13-19% respectively at 1.5 m and 10 m. The soils are silty sand with low plasticity depiting low to medium swelling potential. Conclusively, the subsurface on which the foundation of the industrial structures will be located within the study area is safe and fairly competent for any engineering work. Owning to the water lodge nature of the area it is advice that the building should rest on pill between 5 m and 10 m depth. Keywords: Foundation; VES; Geotechnical; Geoelectric layer, Pill
GeoScience Engineering
The subsurface of a proposed site for building development in Mowe, Nigeria, using Standard Penetration Test (SPT), Cone Penetrometer Test (CPT) and Horizontal Electrical Profiling (HEP), was investigated with the aim of evaluating the suitability of the strata for foundation materials. Four SPT and CPT were conducted using 2.5 tonnes hammer. HEP utilizing Wenner array were performed with inter-electrode spacing of 10 – 60 m along four traverses coincident with each of the SPT and CPT. The HEP data were processed using DIPRO software and textural filtering of the resulting resistivity sections was implemented to enable delineation of hidden layers. Sandy lateritic clay, silty lateritic clay, clay, clayey sand and sand horizons were delineated. The SPT “N” value defined very soft to soft sandy lateritic (<4), stiff silty lateritic clay (7 – 12), very stiff silty clay (12 - 15), clayey sand (15-20) and sand (27 – 37). Sandy lateritic clay (5-40 kg/cm2) and silty lateritic clay (25 ...
Engineering structures are designed and constructed with an air of lifelong expectancy. Moreover, building foundation may experience failure due to presence of concealed geologic features such as cavity and shear zones which can lead to subsurface subsidence. Hence, it is imperative, prior to building construction, to investigate the physical properties of foundation soils and determine its suitability for design and construction of building structures. In the light of this, a geoelectric survey, involving three (3) electrical dipole-dipole array and geotechnical analysis methods were carried out around a distressed building at Oroke High School, opposite Adekunle Ajasin University, Akungba Akoko to establish the cause of failure for the structures foundation via delineating the subsurface structural features. The field electrical data were plotted on log-log graph sheets and the resulting curves were interpreted qualitatively by visual inspection, and quantitatively via partial curve matching and computer iteration techniques. For the geotechnical analysis, a total of twelve (12) soil samples were taken from different locations of about 30 meters intervals, at the depth of 1.5 meters. The pseudo-section and electrical sections indicate that the subsurface is heterogeneous in geological composition. The 2D dipole-dipole resistivity and pseudo-section delineated zones having resistivity values ranging from 200 to 700ohm meter, and those approaching infinity all within a depth of 0-5 m, the resistivity values of 27 to 139ohm meter suggest the presence of clay. The geoelectric section identified three subsurface geologic layers comprising clay /sandy, clay top soil / sub grade soil, clay / sandy clay and sand weathered layer and the basement (fresh) beneath the failed segment. Additionally, prominent fractures were discovered within some areas on the pseudo-sections. The results of the laboratory tests also included those of natural moisture content, specific gravity, grain size distribution curves, Atterberg limit, compaction test and California Bearing Ratio (CBR). In conclusion, electrical resistivity method was found to be an effective measure or tool in the site characterization. The soil/rock in these zones may require reinforcement in order to enhance its bearing capacity and increase the life span of the engineering foundation.
An engineering site characterization using geophysical methods namely Very Low Frequency (VLF) electromagnetic, Vertical Electrical Sounding (VES), and magnetic methods have been completed at a site located at Aba-Oyo area, Akure. This was aimed at evaluating the geoelectrical, magnetic and electromagnetic parameters of near surface earth materials and its engineering implications, towards the construction of an engineering structure. Ten VLF and magnetics profiles were occupied, with traverse length varying from 50-70 m; and twelve VES positions across the study area. Quantitative interpretation was initially carried out on the VES using the partial curve matching technique and 1-D forward modelling with Win Resist software. Quantitative interpretation of the VLF revealed some conductive zones which were characterized as geologic structures such as fractures, faults, and lineament which can serve as pathway for fluid flow. Four lithologic units were delineated namely top soil, lateritic layer, weathered layer and fresh basement. The top soil resistivity varies from 44-181 Ωm and thickness ranges between 0.4 and 2.0 m, lateritic layer resistivity varies between 20-174 Ωm and thickness ranges between 1.7-5.2 m, while the weathered layer resistivity varies between 20-310 Ωm and thickness between 1.4-7.4 m. Bedrock ridges and depressions were identified on the overburden thickness map. Low resistivity values of the top soil suggest high clay content. Result shows that the subsurface earth materials differ in their competency due to the variation in resistivity value. Possible source of failure identified include incompetent earth layers characterized by low resistivity, laterally inhomogeneous subsurface layer and conductive zones identified as fractures and faults. It is concluded that a high rise building or structure with a strip footing foundation will require engineering intervention such as pilling to a depth of about 8-12 m.