Geoelectric Investigation of the Groundwater Potential of Moniya Area, Ibadan

Geoelectric measurements using the Vertical Electrical Sounding (VES) method were carried out in Moniya, Akinyele Local Government, Oyo State, Nigeria, using the ABEM terrameter SAS 300B . The objectives of the study were to investigate the aquifer characteristics and groundwater potential of the subsurface formations. Seventeen profiles were carried out using the Schlumberger array configuration. The data was interpreted using the conventional curve matching and computer iteration methods. Results show that four major curve types were identified, namely: A, H, KH and HA. The top layer has resistivity value ranging from 61.8 to 504.3 ohm-m showing that it consists of clayey sand and sandy clay, with maximum layer thickness of 3.5 m. The resistivity of the second layer which is the weathered zone ranges from 19.7 to 724.6 ohm-m while the thicknesses vary between 0.7 to 30.3 m. These VES stations: 9, 11, 16, and 17 are fourth layer region. The third layers constitute the weathered layer which has resistivities from 13.7 to 95.3 ohm-m while it’s layer thicknesses vary from 12.6 to 44.6 m the layer will be good for well sitting. VES stations 9, 6, 7, 12, 14, and17 are the locations that will be recommended for deep well sitting, because they have highest thickness of both weathered zone and fractured zone respectively which are good for groundwater storage

Foundation Settlement Determination: A Simplified Approach

The heterogeneous nature of the subsurface requires the use of factual information to deal with rather than assumptions or generalized equations. Therefore, there is need to determine the actual rate of settlement possible in the soil before structures are built on it. This information will help in determining the type of foundation design and the kind of reinforcement that will be necessary in constructions. This paper presents a simplified and a faster approach for determining foundation settlement in any type of soil using real field data acquired from seismic refraction techniques and cone penetration tests. This approach was also able to determine the depth of settlement of each strata of soil. The results obtained revealed the different settlement time and depth of settlement possible

Attenuation Variability in Porous Media: Effects on Phase Delay and Quality Factor

Electromagnetic methods of surveying involve the propagation of time varying low frequency electromagnetic fields in and over the earth. This gives rise to a secondary electromagnetic field and a resultant field which is picked up by suitable receiving coil. This research work modelled electromagnetic method of survey using a Cathode Ray Oscilloscope and a signal generator. This work was aimed at relating the effects of phase delay and the quality factor of a propagating signal to some properties of the homogeneous medium, like porosity (compaction), permeability and hydraulic conductivity. River bed sand was used as the sample, it was washed, oven dried, sieved into different grain sizes and the porosity was determined. Each sample was packed in a square box and connected to a signal generator and an oscilloscope. Two sinusoidal waves of the same frequency, but different amplitudes were sent from a signal generator and the measurement was taken at different frequencies. Graphs of frequency were drawn each against phase delay and Q – factor. Graphs of porosity were drawn each against phase delay and Q – factor. In conclusion, we observed that the porosity of a material increased with the decrease in the mixture of its grain size and signals were more attenuated at lower frequencies but as the frequency of the input signal was increased, the material became more permeable to the passage of the input signal. Keywords: porosity, attenuation coefficient, phase delay, quality factor and electromagnetis

Application of Shallow Seismic Refraction Method and Geotechnical Parameters in Site Characterization of a Reclaimed Land

The recent incessant cases of building collapse have made it necessary for building site to be characterized before they are developed especially when the land is reclaimed from water bodies. On the basis of the above, both geophysical and geotechnical methods are engaged to determine the subsurface structure of a land for construction purposes. In this research effort, near surface seismic refraction method together with relevant geotechnical methods were used to characterize the subsurface condition of the study site. Nine seismic refraction profiles were surveyed with some of the profiles laid parallel and some others overlain one another. The result of this study revealed three geologic layers in the site with varying geotechnical parameters. The Young’s modulus, bulk modulus and shear modulus all have values that ranges from 0.071-25.685, 0.083-30.042 and 0.0286-10.395 GPa respectively in the site. From these results, it can be concluded the third layer having the highest value of geotechnical parameters is the most competent and this layer is between 7.5 m and 18 m into the subsurface. The information obtained from other geotechnical methods in the site confirmed the results of this study. Thus, near surface seismic refraction method is recommended for a non-invasive, non-cumbersome and reliable site characterizatio

Application of Geophysical and Geotechnical Methods to Determine the Geotechnical Characteristics of a Reclaimed Land

Near-surface seismic refraction method and electrical resistivity methods were used to characterise the subsurface of a site reclaimed from water bodies, in order to determine the depth to the most competent layer for construction purposes. Nine seismic refraction profiles were surveyed and the data was interpreted using SeisImager software package. Also, twelve vertical electrical soundings were carried out and the acquired data was interpreted using WinResist computer package. The seismic refraction method delineated three layers while the electrical resistivity method revealed between four and five geoelectric layers. The result of the seismic refraction method showed that the third layer is the most competent layer having the highest elastic moduli. Furthermore, the resistivity method revealed that the third geoelectric layer is the most competent having resistivity ranging between 23.3 and 1107.2m . It was also discovered that the depth to the most competent layer is between 7 m and 18 m in the subsurface. It was concluded that piling will be the most appropriate foundation for any building in the study area

Investigation to determine the vulnerability of reclaimed land to building collapse using near surface geophysical method

Adequate knowledge of the geology and the structures of the subsurface would assist engineers in the best way to carry out constructions to avoid building collapse. In this study, near surface seismic refraction method was used to determine the geotechnical parameters of the subsurface, the results obtained were correlated with the result of borehole data drilled in the study area. The results of seismic refraction method delineated mostly two distinct layers with the first layer having the lower geotechnical parameters. It was observed that in the first layer, the Young’s modulus ranged from 0.168 to 0.458 GPa , shear modulus ranged between 0.068 and 0.185 GPa, the bulk modulus ranged between 0.106 and 0.287 GPa while the bearing capacity ranged from 0.083 to 0.139 MPa. On the other hand, in the second layer, the Young’s modulus ranged between 3.717 and 7.018 GPa, shear modulus ranged from 1.500 to 2.830 GPa while the bulk modulus ranged from 2.383 to 4.449 GPa. Significantly, the formation of the second layer appeared to be more competent than the first layer, therefore engineering construction in this geological setting is recommended to be founded on the second layer at depth ranging between 7 and 16 m

Evaluation of Geotechnical Parameters using Geophysical Data

The financial implications and the time required for carrying out a comprehensive geotechnical investigation to characterize a site can discourage prospective private residential building developers, especially where a large area of land is to be investigated for construction purposes. Also, most of the geotechnical test procedures utilized during site investigation only provide information on points tested in the subsurface. This research method suggests an approach of investigating the subsurface condition of a site in order to obtain key subsoil geotechnical properties necessary for foundation design for proposed engineering facilities. Seismic wave velocities generated from near surface refraction were combined with percussion drilling and cone penetration tests to obtain a comprehensive geotechnical investigation. From the results of the seismic refraction method, the bulk density of the soil, Young’s modulus, bulk modulus, shear modulus and allowable bearing capacity of a competent layer that can bear structural load at the particular study site were determined. The most competent layer was found within the depth observed by geotechnical methods. In addition, regression equations were developed in order to directly obtain the bulk density of the soil, Young’s modulus, bulk modulus, shear modulus and allowable bearing capacity from the primary wave velocities

Application of 2D electrical resistivity imaging and cone penetration test (CPT) to assess the harzadous effect of near surface water on foundations in Lagos Nigeria

Adequate information on the condition of the subsurface is very important for site evaluation for engineering purposes. In this study two dimensional (2D) geoelectrical resistivity survey and cone penetration tests were conducted to study the hazardous effect of excess near surface water on the foundation of building in a reclaimed land located at Victoria Island area of Lagos State. The results of the inverted 2D geoelectrical resistivity data revealed three distinct geoelectrical layers characterized by low to moderate electrical resistivity of 2.23 and 129 Ωm and 9.46 to 636 Ωm respectively. The topsoil is characterized by wet sandy soil, which is underlain by sandy clay and banded at the below by a geologic formation of low resistivity which is suspected to be clay. The clay material may be responsible for the excess water retention observed in the area. The CPT method on the other hand revealed a geological formation of low resistance to penetration between 2-3 kg/cm2 from the topsoil to a depth of 7 m, which may be the effect of excess water in the near surface. This study revealed that the foundation of building may not be founded directly on the soil in any reclaimed land as this may result in collapse as a result of upward migration of water to the near surfac

Evaluation of Index Properties of Lateritic Soils in Ado Ekiti Metropolis South Western, Nigeria

The aim of this research is to evaluate the index properties of lateritic soils in Ado Ekiti Area of Ekiti State, Nigeria. The areas will be divided into Five Zone viz:: Ado-poly,Ado-Ikere, Ado-Housing, Ado-Ilawe and Ado-Adebayo respectively for the sampling process. Eighteen soils samples were collectedto cover Ado-Ekiti and environs in Ado Ekiti suburbs. The research comprise field data collections. ArcGIS 10.1 will be used for quantitative analysis of the field data. Measurement of depth at sample collection points will be taken using GIS, the geographic coordinate and other details using Global Positioning System (GPS) handheld instrument (Garmin 76). Laboratory test such as: Natural Moisture Content (NMC) , Specific gravity, Grain size analysis, Liquid Limit , Plastic Limit, Linear Shrinkage. The visual soil profile description of all trial pits investigated, reveal little variation within the soil strata. The laboratory results indicated that the particle size gradation for gravel ranged from 1 to 44 %, sand ranged from 26 to 77% and fines ranged from 8 to 46%; natural moisture content ranged from 1.1 to 18.7%; specific gravity ranged from 2.23 to 2.79; the bulk density ranged from 1134. to 1625. kg/m3, ; the liquid limit ranged from 25 to 65%, plastic limit ranged from 17 to 43%, plasticity index ranged from 10 to 30%; linear shrinkage ranged from 3.6 to 15.5%;According to America Association of State Highway and Transport Officials (AASHTO) soil classification and Unified Soil Classification System (USCS), all the samples can be classified as follows for all the five zone investigated : A-2-4, A-2-6,A-6 ,A-7-5 for (AASHTO) and CL,MH and CH materials. This research work has provided data for engineers, designers and contractor for the use of this lateritic soils materials for construction work and has prevented possible difficulties, delays and additional expenses during construction due to inadequate geotechnical information within this metropolis It is recommended that all contractors should ensure that the testing and quality control of lateritic materials and project site within this area is done before the commencement of work on sit

Analysis of Geotechnical Parameters from Geophysical Information

In our part of the world where legislations related to site investigations before constructions are not strictly enforced, it may be difficult to carrying out a comprehensive geotechnical investigation to characterize a site because of the expenses and the time involved. Another factor that can discourage a developer is the fact that most of the geotechnical tests procedures utilized during site investigations, to a certain extent, alter the existing environment of the site. This study suggests a quick, non-destructive and non-intrusive method of obtaining key subsoil geotechnical properties necessary for foundation design for proposed engineering facilities. Seismic wave velocities generated from near surface refraction method was used to determine the bulk density of soil, Young’s modulus, bulk modulus, shear modulus and allowable bearing capacity of a competent layer that can bear structural load at the particular study site. Also, regression equations were developed in order to directly obtain the bulk density of soil, Young’s modulus, bulk modulus, shear modulus and allowable bearing capacity from the compressional wave velocities. The results obtained correlated with the results of standard geotechnical investigations carried out