Subsurface Layer Characterisation Research

Subsurface Layer Characterisation Research SUBSURFACE LAYER CHARACTERISATION FOR ENGINEERING PURPOSES USING VERTICAL ELECTRICAL SOUNDING IN BANANA ISLAND, LAGOS, NIGERIA OLADUNJOYE, H.T., 2OLALEYE, A.O. ABSTRACT Seven (7) vertical electrical sounding stations along two traverses were used to study the depth to competent formation for foundation of engineering structures in Banana Island of Lagos. The study is meant to unravel the presence of problem soils that can be inimical to structures.   The sounding data used in this study was acquired using Schlumberger Electrode Configuration. The VES data were interpreted into a model curve using forward modelling software called Winglink. The interpretation parameters (layer resistivities and thicknesses) for each VES point were grouped into three geo-electric sections to represent the 2-D models of the subsurface layers in the study area. The final interpretation results (resistivities and depths) modelled as geoelectrical sections and pseudosections were compared within the surveyed area and correlated with the borehole log-derived depths to determine a probable depth for foundations of high rise building. The study concluded that the geophysical investigation is of great significance in partial curve matching interpretation technique gives the most consistently low percentage deviation error margins amongst the three VES preliminary interpretation techniques. There is consistent increase in depth prediction error, with depth, in all the interpretation techniques. INTRODUCTION Geophysical resistivity techniques are based on the response of the earth to the flow of electrical current. In all methods, an electrical current is passed through the ground and the resulting potential electrodes allow us to record the resultant potential difference between the current electrode is measured. The apparent resistivity is then a function of the measured impedance (ratio of potential to current) and the geometry of the electrode array. Depending upon the survey geometry, the apparent resistivity data are plotted as 1-D soundings, 1-D profiles, or in 2- D cross-sections in order to look for anomalous regions. In the shallow subsurface, the presence of water controls much of the conductivity variation. Measurement of resistivity (inverse of conductivity) is, in general, a measure of water saturation and connectivity of pore space. This is because water has a low resistivity and electric current will follow the path of least resistance. Increasing saturation, increasing salinity of the underground water, increasing porosity of rock (water-filled voids) and increasing number of fractures (water-filled) all tend to decrease measured resistivity. Resistivity measurements are associated with varying depths depending on the separation of the current and potential electrodes in the survey, and can be interpreted in terms of a lithologic and/or geohydrologic model of the subsurface. The choice for Direct Current (DC) resistivity survey in this project is as a result of its ability to provide a quick synoptic picture of lithological and groundwater characteristics in terms of its apparent resistivity contrast. In this work the electrical resistivity character collected were model with Winresist and Winglink inversion software. The layers parameters (resistivities and thicknesses) obtained from data processing were then inverted with Winglink to provide two-dimensional images of the subsurface apparent resistivity variation (Pseudosection). However, knowledge on the geology of the area from acquired borehole log has played a vital role in determining the best fit model. MATERIALS AND METHOD OF STUDY The vertical electrical resistivity is used to determine the subsurface resistivity distribution and depth of the sub-surface layers with the aid of electrical resistivity meter. In this study, Schlumberger array of electrical resistivity method was adopted because of the low cost of the field operation, reduced logistics man power and also faster. A total of Six (6) vertical electrical sounding (VES) were measured within the area. The resistivity measurement is taken by introducing small portion of electricity through two current electrodes (A and B) and measuring the resultant voltage drop between a pair of potential electrodes (M and N). A simple calculated value of apparent resistivity is the parameter bearing the information for the characteristics of the subsoil (Tonkov, 2008). From the foundation of electrical resistivity theory is the ohms law (Grant and West, 1965; Dobrin and Sarvit, 1988):            Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   (1) Where Ï  is the resistivity, R is the resistance, L is the length of the conducting cylinder and A is the cross sectional area. For the solid earth, whose material is predominantly made up of silicates and basically non conductors, the presence of water in the pore space of the soil and in the rocks fractures enhances the conductivity of the earth when an electrical current I is passed through it, thus making the rocks a semi conductor.   Since the earth is not like a straight wire and it is not an anisotropic, then Equation 1 can be customized as:   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   (2) Where change in voltage and r is is the radius of current electrodes hemisphere. Since the earth is not homogeneous, Equation 2 is used to define an apparent resistivity which is computed as the product of the geometric factor and the resistance recorded in the electrical resistivity meter and resistivity the earth would have if it were homogeneous (Grant and West, 1965;):   Ã‚  Ã‚  Ã‚     Ã‚  Ã‚     Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚   (3) Where, 2Ï€r is then define as the geometric factor (G) fixed for a given electrode configuration and is dependent on the electrode arrangement. The Schlumberger electrode configuration was used for this study. The geometric factor is thus given as:   Ã‚  Ã‚   (4) Where AB is the distance between two current electrodes, MN is the distance between two potential electrodes. LOCATION AND GEOLOGY OF THE STUDY AREA The study area is located in the south-eastern part of Lagos State between Latitudes 6 ° 25 to 6 ° 28 North of the Equator and Longitudes 3 ° 24 to 3 ° 30 East of the Greenwich Meridian (Fig.1.1). The study area Lekki and its environ issituated within the western Nigeria coastal creeks and lagoon developed by barrier beaches associated with sand deposition (Pugh, 1954). It forms part of the Lagos lagoon system known as the largest of the four lagoon system in the gulf of guinea coast (Adepelumi and Olorunfemi, 2000). Banana Island is an artificial island in Lagos State, Nigeria. It is located in the Lagos Lagoon and attached to the North-Eastern Ikoyi Island by a dedicated road strip which is linked to the existing road network. The banana-shaped Island is approximately 1,630,000 square metres in size (less than a square mile) and is divided into 536 plots (of between 1000 and 4000 square metres in size) mainly arranged along cul-de-sacs, so designed to enhance the historically residential nature of Ikoyi. Banana Island is an artificial island reclaimed from portions of the Lagos Lagoon, topographic elevation obtained at the site averaged 4 metres above mean sea level. The study area is located within the coastal region of Nigeria with a climate of long wet season (April to October) and short dry season (November to March). Average annual precipitation is above 2000mm and serves as a source of groundwater recharge. The area is susceptible to flooding after heavy rainfall during the wet season. Nigeria lies in an extensive Pan-African mobile belt which separates the West African and Congo Cratons. The belt is interpreted to have evolved from the continental collision between the West African craton and the Pan-African belt (Black et al., 1979; Caby et al., 1981). Geochronologically, the Precambrian rocks of Nigeria can be grouped into four major classes (Liberian Orogeny 2800  ± 200 Ma, Eburnean Orogeny 2000  ± 200 Ma, Kibaran Orogeny 1100  ± 200 Ma and The Pan-African Orogeny 600  ± 150 Ma). These classes correspond with the four orogenic events that have punctuated the Precambrian history of Africa (Odeyemi, 1979). Figure 2.1: Regional Geological Map of Nigeria (Modified after Ajibade et al., 1988) Coastal Nigeria comprises two sedimentary basins: The Benin-Dahomey basin and the Niger Delta basin separated by the Okitipupa ridge. The rocks of the Benin basin are mainly sands and shales with some limestone which thicken towards the west and the coast as well as down dips to the coast. Recent sediments are underlain by the Coastal Plains Sands which is then underlain by a thick clay layer the Ilaro Formation and other older Formations (Jones and Hockey, 1964). The Coastal Plains Sands aquifer is a multi-aquifer system consisting of three aquifer horizons separated by silty or clayey layers (Longe et al., 1987). It is the main aquifer in Lagos Metropolis that is exploited through boreholes for domestic and industrial water supply. The sedimentary rocks of Lagos State are composed of five (5) sedimentary formations (Jones and Hockey, 1964) viz: Abeokuta Formation, Ewekoro Formation, Ilaro Formation, the Coastal Plains Sands and the alluvial deposits. The coastal plains sand also known as the Benin Formation stretches across the Dahomey basin into the Niger Delta Basin. The geological formations of the study area composed of sediments laid down under fluviate, lascustrine and marine environments. These sediments grade into one another and vary widely in lateral extent and thickness (Adepelumi and Olorunfemi 2000). Longe et al., (1987) classified the aquifer into three types. Quantitative interpretation of the curves involved partial curve matching using two-layer Schlumberger master curves and the auxiliary K, Q, A and H curves. Output from the quantitative interpretation was modelled using computer iteration. The Resist Version 1.0 interpretation software was used for iteration and presentation of the curves (see Figures 3a f). RESULTS AND DISCUSSIONS The apparent resistivities from the field plotted on a log-log graph survey against the corresponding half Schlumberger electrode spacing was interpreted using the computer iteration technique. The initial model was deriving by winresist software by entering layer parameters from partial curve process as the starting parameters. The resulting models were then iterated till the best fit curve as attained. In all, there was a large value for root mean square (r.m.s) error resulting mostly from the scattered point data observed where half Schlumberger electrode spacing is greater than 32m. In order to view the resistivity distribution of the whole surveyed area, the result of the soundings data linearly and vertically interpolated into two dimensional pseudosections. The borehole records from the geo-technical investigation were used as a control in interpreting the VES data acquired in this study. Interpretation of the geo-electric curves was essentially based on the fact that resistive materials constitutes zones of interest for engineering construction, considering that clay and organic materials are conductive and typified by low resistivity values(reference). The outputs from the manual interpretation were modelled using computer iterations. Resist Version 1.0 software was utilized for the iterations. The curve types obtained are 3 layer H (VES 1), 4 layer QH (VES 2, VES 3 and VES 6) and 5 layer QHK (VES 4 and VES 5), as shown in Figures 3a f. VES 1 and VES 6 with RMS-error (Root Mean Square) of 11.7 and 10.4 respectively present better quality data than VES 2 to VES 5 with RMS-error ranging from 12.7 to 20.8, thus the interpretation of the geo-electric curves at VES 1 and VES 6, present more reliable results. From the iteration of VES 1, depth to competent bedrock (sand) is 39.6 metres, while depth to competent (sand) layer at VES 6 is 39.8 metres, this is signified by the rising segment of the curve at both VES stations, typified by a relatively resistive material (5 105 à ¢Ã¢â‚¬Å¾Ã‚ ¦-m). CONCLUSION This paper describes the possibility of locating a competent formation for high rise building in area around Banana Island Ikoyi using Schlumberger array. The results of the interpretation of field survey reveal only the presence such formation in depth close to 10m. At this depth saturated sandy clay can be obtain virtually for all the VES stations. This saturated sandy clay formation provides good foundation support for any high rise due to the fact that the liquefaction potential is very low compare to all other formation inferred from geologic section. REFERENCE Alile, M.O., S.I. Jegede and O.M. Ehigiator, 2008. Underground water exploration using electrical resistivity method in Edo State, Nigeria. Asian J. Earth Sci., 1: 38-42. Anderson, N. L. Selection of Appropriate Geophysical Techniques: A Generalized Protocol Based on Engineering Objectives and Site Characteristics. Proc., 2006 Highway Geophysics- NDE Conference, 2006, pp. 29-47. Available at http://2006geophysics.mst.edu/. Anderson, N. L., A. M. Ismail, and T. Thitimakorn. Ground-Penetrating Radar: A Tool for Monitoring Bridge Scour. Environmental and Engineering Geoscience, Vol. 13, 2007, pp. 1-10. Dobrin, M.B. and C.H. Savit, 1988. Introduction to Geophysical Prospecting. 4th Edn., McGraw Hill Book Co., New York. Dogara, M.D., B.M. Dewu and C.O. Ajayi, 1998. Groundwater potential of Romi, Kaduna. Nig. J. Physics., 10: 85-90. Grant, F.S. and G.F., West, 1965. Interpretation Theory in Applied Geophysics. McGraw-Hill, New York. Nwankwo L.I., P.I. Olasehinde and E.B. Babatunde, 2004. The use of electrical resistivity pseudo-section in elucidating the geology of an east-west profile in the basement complex terrain of Ilorin, West-Central Nigeria. Nig. J. Pure Applied Sci., 19: 1672-1682. Olasehinde, P.I., 1999. An integrated geological and geophysical exploration for groundwater in the basement complex of west central Nigeria. Water Resourses, 10: 46-49. Olasehinde, P.I., A.E. Annor and P.C. Pal, 1986. A geological evaluation of a prospective site for a weir on river Oyun, Ilorin, Nigeria. 7. Angew Geowiss, 8: 83-90. Olorunfemi, M.O and S.A. Fasoyi, 1993. Aquifer types and the geoelectric/hydrogeologic characteristics of part of the central basement terrain of Nigeria (Niger State). J. Afr. Earths Sci., 16: 309-317. Plummer, C.C., D. McGeory and D.H. Carlson, 1999. Physical Geology. 8th Edn., McGraw Hill Co. Inc., New York, pp: 48-56. Rabiu, A.B, I. A. Adimula, K. Yumoto, J. O. Adeniyi and G. Maeda, 2009. Preliminary results from the magnetic field measurements using MAGDAS at Ilorin, Nigeria. Earth Moon Planets, 104: 173-179. Rahaman, M.A., 1973. Review of the Basement Geology of South Western Nigeria. In: Geology of Nigeria, Kobe, C.A. (Ed.). 2 Edn., Rockview Publishers, Jos, Nigeria. Singh, K.K.K., A.K.S. Singh, K.B. Singh and A. Sinha, 2006. 2D resistivity imaging survey for siting water-supply tube wells in metamorphic terrains: A case study of CMRI campus, Dhanbad, India. The Leading Edge, 25: 1458-1460

Priming Theory Essay

Mass media has the capability to influence people to think based on the media concepts that have been presented to them. In thousands of images that people see on media sources everyday, the strong recall of each image leave marks on the minds of the viewers or readers which often lead to the conclusion that mass media is the influential and powerful tool to deliver messages to the mainstream. From entertainment to business purposes, media plays a very important role in the society. The public does not always notice the strong effects of persuasive advertisements or well-narrated news story presented by media; however, the increasing demands determine the impacts of these media concepts to the people in all aspects. People buy a certain product because of the appealing commercial on television. People conform to the latest fashion trends because the models and endorsers on the magazines. People vote for a certain politician because of constant release of propaganda through newspapers. These are just few of the many examples showing the strong effects of mass media to the public. Even though the people are often unaware of these influential demands and plain consumerism, the society still relies on the ability and credibility of mass media for providing information that would help each cluster function well in the society. This concept has an accurate explanation from the mass communication theorists. The pictures that people see on screen and magazine pages and the attitude of people prior to and upon seeing those images have been discussed and given explanations for the society’s better understanding. Priming is one of the theories that would explain the media concepts and effects of media images to the public. Apparently, the concept of priming will be most effective to examine in the light of other theories in the field of communication like framing and agenda setting. These theories would help the people to understand the concept of priming and its focus on media messages. The Priming Theory During election campaign period, much propaganda are being released on popular media sources like television, radio, newspapers, and even magazines to inform and update the public about the event. Typically, this is the hardest period for the politicians because this is the time when they need to build a rapport with the mainstream and make them aware about their candidacy. This is also the period when the mass media plays a very important role to make them reach the anticipated position in the society (Burstein, 1991). The dissemination of information creates a strong recall to the mainstream and the salient issues on media become the center of attention of the public. Since the awareness of the people is being determined on their level of media exposure and participation, the constant release of advertisements and promotions are done by the politicians to reach all the target people. It has been mentioned that the concept of priming can be explained with the use of other theories; in fact, agenda setting theory serves as the umbrella of priming. Agenda setting suggests that mass media may not be successful in telling the people what to think; however it has been successful in telling the mainstream what to think about. Mass media may not tell people to buy a certain product but the advertisements on television and billboards would affect the behavior of the consumers because of its persuasive appeal. In agenda setting, the media does not command people to conform but rather present the idea alone and let the people do the rest (Birkland, 1998). In other words, the media shows images in a way the people would easily get the messages that are being conveyed on media concepts. According to agenda setting theory, the media highlight a certain issue or certain part of the controversy to make the people put too much attention on the salient issues rather than to those issues that media considers as less important. Apparently, issues help to develop the perceptions of people toward reality. They provide typical categories which organized the knowledge of the mainstream and their experiences in a large semantic framework relevant for communication in the community.

Introduction to Quality Assurance

One of the important aspects of any healthcare organization is the quality assurance mechanism.   Any healthcare organization would have to be professionally competent, ensuring that the processes in the organization would ultimately ensure the safety of the services provided.   The organization should develop an effective strategy of handling the quality issues. It is important that the administrators understand the importance of quality, develop a quality assurance program, implement it in a phased manner over a period of time, release resources needed for quality assurance, utilize appropriate quality tools, develop and maintain processes and develop an appropriate auditing system.   Some of the quality assurance tools utilized include management tools, presentation tools and statistical analysis tools.   Some of the process deployment tools include marketing tools, tools for changing behavior, etc (Software Certifications, 2006). As healthcare sector is a vital industry, it is very important that quality assurance is given prime importance by the organization.   One of the very important aspects is customer satisfaction and reducing risk.   Protection of patients is the most important aspect of quality assurance.   However, not less important is to ensure that cost-effectiveness and responsive attitude is maintained.   All these significantly contribute towards bringing about patient satisfaction (LRQA, 2003). Some of the measures that may be required for quality assurance include:- Having a quality assurance program in priority areas Responding to the needs of the public appropriately Identifying means by which costs can be reduced and implementing a strategy to save costs Developing best practices mechanisms Accreditation in order to improve quality standards Not only achieving certain quality standards but upgrading them frequently Having an effective decision-making and problem-solving process in the organization (Gonzalez, 2006). References: Gonzalez, M. (2006). â€Å"Health Care Sector Reform and Quality Assurance in Costa Rica.’ Retrieved on April 11, 2008, from QA Project Web site: http://www.qaproject.org/pubs/PDFs/costarica.pdf Lloyd’s Register Quality Assurance Limited (2003). â€Å"Quality in the healthcare sector.† Retrieved on April 11, 2008, from LRQA Review Web site: http://www.lrqa.fr/frsite/content/pdf/rev0603.pdf Software Certifications (2006). â€Å"2006 CSQA Body of Knowledge.† Retrieved on April 11, 2008, from Software Certifications Web site: http://www.softwarecertifications.org/csqabok/csqa6cbok4.htm

Fermion Definition in Physics

In particle physics, a fermion is a type of particle that obeys the rules of Fermi-Dirac statistics, namely the Pauli Exclusion Principle. These fermions also have a quantum spin with contains a half-integer value, such as 1/2, -1/2, -3/2, and so on. (By comparison, there are other types of particles, called bosons, that have an integer spin, such as 0, 1, -1, -2, 2, etc.) What Makes Fermions So Special Fermions are sometimes called matter particles, because they are the particles that make up most of what we think of as physical matter in our world, including protons, neutrons, and electrons. Fermions were first predicted in 1925 by the physicist Wolfgang Pauli, who was trying to figure out how to explain the atomic structure proposed in 1922 by Niels Bohr. Bohr had used experimental evidence to build an atomic model which contained electron shells, creating stable orbits for electrons to move around the atomic nucleus. Though this matched well with the evidence, there was no particular reason why this structure would be stable and thats the explanation that Pauli was trying to reach. He realized that if you assigned quantum numbers (later named quantum spin) to these electrons, then there seemed to be some sort of principle which meant that no two of the electrons could be in exactly the same state. This rule became known as the Pauli Exclusion Principle. In 1926, Enrico Fermi and Paul Dirac independently tried to understand other aspects of seemingly-contradictory electron behavior and, in doing so, established a more complete statistical way of dealing with electrons. Though Fermi developed the system first, they were close enough and both did enough work that posterity has dubbed their statistical method Fermi-Dirac statistics, though the particles themselves were named after Fermi himself. The fact that fermions cannot all collapse into the same state - again, thats the ultimate meaning of the Pauli Exclusion Principle - is very important. The fermions within the sun (and all other stars) are collapsing together under the intense force of gravity, but they cannot fully collapse because of the Pauli Exclusion Principle. As a result, there is a pressure generated that pushes against the gravitational collapse of the stars matter. It is this pressure which generates the solar heat that fuels not only our planet but so much of the energy in the rest of our universe ... including the very formation of heavy elements, as described by stellar nucleosynthesis. Fundamental Fermions There are a total of 12 fundamental fermions - fermions that arent made up of smaller particles - that have been experimentally identified. They fall into two categories: Quarks - Quarks are the particles that make up hadrons, such as protons and neutrons. There are 6 distinct types of quarks:Up QuarkCharm QuarkTop QuarkDown QuarkStrange QuarkBottom QuarkLeptons - There are 6 types of leptons:ElectronElectron NeutrinoMuonMuon NeutrinoTauTau Neutrino In addition to these particles, the theory of supersymmetry predicts that every boson would have a so-far-undetected fermionic counterpart. Since there are 4 to 6 fundamental bosons, this would suggest that - if supersymmetry is true - there are another 4 to 6 fundamental fermions that have not yet been detected, presumably because they are highly unstable and have decayed into other forms. Composite Fermions Beyond the fundamental fermions, another class of fermions can be created by combining fermions together (possibly along with bosons) to get a resulting particle with a half-integer spin. The quantum spins add up, so some basic mathematics shows that any particle which contains an odd number of fermions is going to end up with a half-integer spin and, therefore, will be a fermion itself. Some examples include: Baryons - These are particles, like protons and neutrons, that are composed of three quarks joined together. Since each quark has a half-integer spin, the resulting baryon will always have a half-integer spin, no matter which three types of quark join together to form it.Helium-3 - Contains 2 protons and 1 neutron in the nucleus, along with 2 electrons circling it. Since there is an odd number of fermions, the resulting spin is a half-integer value. This means that helium-3 is a fermion as well. Edited by Anne Marie Helmenstine, Ph.D.