Category Vertical electrical sounding ppt

Vertical electrical sounding ppt

Jump to main content. Surface electrical resistivity surveying is based on the principle that the distribution of electrical potential in the ground around a current-carrying electrode depends on the electrical resistivities and distribution of the surrounding soils and rocks.

The usual practice in the field is to apply an electrical direct current DC between two electrodes implanted in the ground and to measure the difference of potential between two additional electrodes that do not carry current. Usually, the potential electrodes are in line between the current electrodes, but in principle, they can be located anywhere. The current used is either direct current, commutated direct current i.

All analysis and interpretation are done on the basis of direct currents. The distribution of potential can be related theoretically to ground resistivities and their distribution for some simple cases, notably, the case of a horizontally stratified ground and the case of homogeneous masses separated by vertical planes e.

For other kinds of resistivity distributions, interpretation is usually done by qualitative comparison of observed response with that of idealized hypothetical models or on the basis of empirical methods. Mineral grains comprised of soils and rocks are essentially nonconductive, except in some exotic materials such as metallic ores, so the resistivity of soils and rocks is governed primarily by the amount of pore water, its resistivity, and the arrangement of the pores.

To the extent that differences of lithology are accompanied by differences of resistivity, resistivity surveys can be useful in detecting bodies of anomalous materials or in estimating the depths of bedrock surfaces. In coarse, granular soils, the groundwater surface is generally marked by an abrupt change in water saturation and thus by a change of resistivity. In fine-grained soils, however, there may be no such resistivity change coinciding with a piezometric surface.

Generally, since the resistivity of a soil or rock is controlled primarily by the pore water conditions, there are wide ranges in resistivity for any particular soil or rock type, and resistivity values cannot be directly interpreted in terms of soil type or lithology. Commonly, however, zones of distinctive resistivity can be associated with specific soil or rock units on the basis of local field or drill hole information, and resistivity surveys can be used profitably to extend field investigations into areas with very limited or nonexistent data.

The electrical resistivity method has some inherent limitations that affect the resolution and accuracy that may be expected from it. Like all methods using measurements of a potential field, the value of a measurement obtained at any location represents a weighted average of the effects produced over a large volume of material, with the nearby portions contributing most heavily.

This tends to produce smooth curves, which do not lend themselves to high resolution for interpretations. Another feature common to all potential field geophysical methods is that a particular distribution of potential at the ground surface does not generally have a unique interpretation.

Although these limitations should be recognized, the non-uniqueness or ambiguity of the resistivity method is scarcely less than with the other geophysical methods.

For these reasons, it is always advisable to use several complementary geophysical methods in an integrated exploration program rather than relying on a single exploration method.

Apparent resistivity is defined as the resistivity of an electrically homogeneous and isotropic half-space that would yield the measured relationship between the applied current and the potential difference for a particular arrangement and spacing of electrodes. An equation giving the apparent resistivity in terms of applied current, distribution of potential, and arrangement of electrodes can be arrived at through an examination of the potential distribution due to a single current electrode.

The effect of an electrode pair or any other combination can be found by superposition. Consider a single point electrode, located on the boundary of a semi-infinite, electrically homogeneous medium, which represents a fictitious homogeneous earth.

If the electrode carries a current I, measured in amperes athe potential at any point in the medium or on the boundary is given by:. The mathematical demonstration for the derivation of the equation may be found in textbooks on geophysics, such as Keller and Frischknecht For an electrode pair with current I at electrode A, and -I at electrode B figure 1the potential at a point is given by the algebraic sum of the individual contributions:.Olusegun O.

Akinpelu 1. Geophysical investigation was carried out around the University Health Sciences of the Osun State University, Osogbo using the Schlumberger technique of the electrical resistivity method. The aim of the study was to evaluate the groundwater potential and to access how protected the aquifer in the area could be to surface pollutants.

Four 4 vertical electric sounding VES data were acquired within the study area. The area under investigation consists of a lateritic topsoil of varying thicknesses which is underlain by a weathered layer and finally the fresh basement. VES 4 is would yield considerable amount of groundwater if developed to a depth of between 15 m to 20 m to take advantage of the basement fractures due to its thick aquiferous zone and the very low resistivity exhibited by the aquifer layer.

The result also shows that the aquifers in VES 1 and VES 4 shows evidence of weak aquifer protective capacity having longitudinal conductance of 0. This suggests that the study area might show good potential for groundwater but the groundwater is not safe. For groundwater development, adequate measure should be made to establish water treatment facility. Water remains one of the vital elements in life. It is very much vital to human existence.

It is one natural resource that is not only essential for the survival of mankind but also for the survival of the natural environment. The availability of water has played a key role in the development of all civilizations.

Indeed, especially in the ancient times, water scarcity prevented the development of settlements [ 18 ]. Social welfare and economic development may also be hampered in the absence of reliable water supplies. This is particularly true of sub-Sahara and Sahara countries, such as Nigeria, where water resources are extremely limited and highly valued as a social and economic good. Higher agricultural use of water has been in the aspect of irrigation of farmlands.

Due to the limited water resources, the role of macroeconomic policies in agricultural water management is vital and undeniable.

ELECTRICAL - PowerPoint PPT Presentation

However, amount of irrigation-equipped areas as share of cultivated areas is low in the world. In addition, agricultural water management has been done poorly in some areas.

According to [ 9 ]sinceaccess to pumped wells has caused a rapid worldwide increase in groundwater development for municipal, industrial, and agricultural purposes.To browse Academia. Skip to main content. Log In Sign Up. Zeyad Abu Heen. Seawater intrusion is serious problem especially in sounding; VES; sea coastal areas. Lithology and hydrochemistry data from 12 bore holes were used to integrate the results. The problem of the salinization of groundwater 1.

Introduction: aquifers arises in coastal areas, where the excessive Securing water for sustainable development is a pumping of unconfined coastal aquifers by water major challenge facing the global community.

Vertical Electrical Sounding (VES)

At wells leads to the intrusion of sea water. This present, developing countries face environmental negative effect of human activity has been recorded pressure induced by high population community, in many areas of the world.

vertical electrical sounding ppt

Hence, this problem is rapid urbanization, and deficient water sector likely to arise in areas like Gaza Strip that has poor services reflecting on improper management of water resources low precipitation and high water resources UN, ; WHO, Gaza Mediterranean regions where semi-arid conditions Strip is classified as a semi-arid region and suffers lead to excessive pumping, high extraction rate and from water scarcity. Ground water is the main source low recharge and associated with urban area of water in Gaza Strip.

Water analysis results revealed Petalas et al. The water Strip Khan younis and Rafahto delineate the sea sector suffers a lot of problems in terms of quantity and water intrusion into the freshwater aquifer in the study quality. Abu El-Naeem et al. Water demand in the Gaza Strip is increasing continuously 2. Geological and Hydrogeological Setting of the due to economic development and population increase Study Area: resulting from natural growth and returnees, while the Khan Younis and Rafah governorates are the southern water resources are constant or even decreasing due to part of Gaza Strip.

Gaza Strip is a narrow coastal strip urban development Hamdan, Identification and modeling of seawater intrusion of the Gaza Strip aquifer has been studied and proposed by Qahman,and Qahman et al. DC surface resistivity methods have been used for groundwater research for many years.

It can be used to map the freshwater-saltwater interface and for studying conductive bodies of hydrogeological interest Keller and Frischknecht, ; Zohdy et al. The total area of Gaza Strip is about km2 and its length is approximately 45 km along the coast line Vertical electrical sounding VES with Schlumberger array and its width ranges from 6 to 13 km. Gaza Strip as a low-coast technique and veritable tool in includes five Governorates: Northern, Gaza, Middle, groundwater exportation is more suitable for Khan Younis, and Rafah.

The population is growing by density of about Nejad et al. The Saqiya group about A geoelectrical survey using the electrical resistivity method was carried out in the Curin basin, Iran to investigate the sub-surface layering and evaluation of the aquifer characteristics. Applying the Schlumberger array, a total of vertical electrical soundings were conducted along 26 profiles.

Quantitative and qualitative Interpretations of data were carried out. The maximum depth of this layer is 60 m that lies in northwest and southeast of area. In other area, it is less than 60 ohm-m, corresponds probably to Shale. From the quantitative interpretation of VES curves, the boundary of aquifer was determined.

vertical electrical sounding ppt

Finally, zones with high yield potential in the aquifer were determined. Southeastern and northwestern parts of the aquifer were the best parts for choosing the drilling sites and future development. Direct current resistivity method is a common tool for surveying water in arid areas. It is well known that this method can be successfully employed for ground water investigations, where a good electrical resistivity contrast exists between the saturated and unsaturated layers. The vertical electrical sounding with Schlumberger array as a low-cost technique and veritable tool in groundwater exploration is more suitable for hydrogeological survey of sedimentary basin.

vertical electrical sounding ppt

This method is regularly used to solve a wide variety of groundwater problems. Some recent studies include: determination of zones with high yield potential in an aquifer Ahilan and Kumar, ; George et al. Study area: The study was conducted in an arid region in the Curin basin.

It is located south of the Zahedan city in the southeastern part of Iran Fig. Figure 1 shows also the positions of VES measurements. The average annual rainfall is around 73 mm. It covers an area of about km 2. Method of investigation: Electrical resistivity techniques measure earth resistivity by passing an electrical current into the ground and measuring the resulting potentials created in the earth.

This method involves the supply of direct current or low-frequency alternating current into the ground through a pair of current electrodes and the measurement of the resulting potential through another pair of electrode called potential electrodes.

Since the current is known and the potential can be measured, an apparent resistivity can be calculated.

vertical electrical sounding ppt

Then, the sounding curves were interpreted to determine the true resistivities and thicknesses of the subsurface layers. The resistivity of the subsurface material observed is a function of the magnitude of the current, the recorded potential difference and the geometry of the electrode array used.

The depth of penetration is proportional to the Schlumberger array which uses closely spaced potential electrodes and widely spaced current electrodes. In general, the depth of infiltration is small in this method and only shallow subsurface layers have been surveyed Danielsen et al. A total number of Vertical Electrical Soundings VES with a distance of m were conducted along 26 geoelectric profiles, in order to evaluate the geoelectrical setting of the Curin basin, south of Zahedan city, Iran Fig.

The soundings are arranged along profiles ranging approximately East-West. The profiles were spaced m each from the other. The Schlumberger electrode configuration having a maximum current electrode spread of m was used. The current electrode spacing begins with a distance equal to 2 m and extends up to m.

Lecture 11: Electrical Resistivity Survey

The field curves were interpreted by the well-known method of curves matching with the aid of Russian software IPI7. The results of the interpretation are represented in the form of the resistivity values that can be used for preparing the isoapparent electric resistivity map and the geoelectric cross sections.

These sections reflect both lateral and vertical variations in resistivity. The field results of the study are presented in both qualitative and quantitative interpretations. In the qualitative interpretation the shape of the field curve is observed to get an idea qualitatively about the number of layers and the resistivity of layers.

vertical electrical sounding, Resistivity method for water exploration

The results of this method of interpretation involved isoapparent electrical resistivity maps and geoelectrical pseudosections. In the quantitative method geoelectrical parameter i. The main objective of the quantitative interpretation of VES curve is to obtain the geoelectrical parameters and geoelectric section. It is hoped that the results of this study could also be used to determine the groundwater potentials of the study area.

Isoapparent electric resistivity maps: The isoapparent resistivity maps reflect the lateral variation of apparent resistivity over a horizontal plane at a certain depth.After you enable Flash, refresh this page and the presentation should play.

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Tags: electrical connectivity. Latest Highest Rated. Potential distribution in a Homogeneous Medium Apparent and true resistivity Potential and current distribution across boundary 3 Cont. Basic Exploration Geophysics. John Wiley Sons Lowrie, W. Fundamentals of Geophysics. Cambridge University Press. In these methods, an electrical current is passed through the ground and two potential electrodes allow us to record the resultant potential difference between them, giving us a way to measure the electrical impedance of the subsurface material.

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. 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. Increasing compaction of soils or rock units will expel water and effectively increase resistivity.

Air, with naturally high resistivity, results in the opposite response compared to water when filling voids. Whereas the presence of water will reduce resistivity, the presence of air in voids should increase subsurface resistivity.

Data are termed apparent resistivity because the resistivity values measured are actually averages over the total current path length but are plotted at one depth point for each potential electrode pair. Two dimensional images of the subsurface apparent resistivity variation are called pseudosections. Data plotted in cross-section is a simplistic representation of actual, complex current flow paths.

Computer modeling can help interpret geoelectric data in terms of more accurate earth models. Active Methods Induced Sources A signal is injected into the earth and then measure how the earth respond to the signal. Factors that affect the measured potential, and thus can be mapped using this method include the presence and quality of pore fluids and clays. Our discussions will focus solely on this method.

It employs measurements of the transient short-term variations in potential as the current is initially applied or removed from the ground. It has been observed that when a current is applied to the ground, the ground behaves much like a capicitor, storing some of the applied current as a charge that is dissipated upon removal of the current.

In this process, both capacity and electrochemical effects are responsible. IP is commonly used to detect concentrations of clay and electrically conductive metallic mineral grains. Measurable electrical potentials have also been observed in association with ground-water flow and certain biologic processes. The only equipment needed for conducting an SP survey is a high-impedance voltmeter and some means of making good electrical contact to the ground.

Electromagnetic EM - This is an active method that employs measurements of a time-varying magnetic field generated by induction through current flow within the earth.A Vertical electrical sounding or VES is a 1D resistivity method that provides deep information of the subsurface with minimal equipment and personnel.

It is one of the oldest methods for acquiring resistivity and one of the least expensive to conduct per unit depth. The VES method can be quite versatile for reconnaissance surveying or when there are equipment limitations.

The data from vertical electrical sounding are more sensitive to general electrical structure than other 1D electromagnetic methods, such as TDEM, because high resistivity contrasts are better resolved with VES.

The plot highlights raw data, inversion model fit to the raw data, and the resulting 1D resistivity-based stratigraphic interpretation. HGI has conducted VES surveys alone and in conjunction with other methods, such as microgravity or induced polarization.

For example, the gravity information can be used to map the geometry of a basin while the 1D resistivity data can provide the stratigraphic structure and location of evaporites.

In this way, the model produced from the data can be combined into a single coherent understanding of the subsurface. The example below shows an mile cross section 18, m through a basin in the southwestern United States. Eleven vertical electrical soundings were acquired and each location of the transmitter and receiver were recorded to ensure proper geo-referencing into the inversion software. The results show coherent layering across the profile and these data can be used to interpret faults, bedrock, and clay lenses.

Subsurface Imaging, Innovative Solutions. The VES method is quite versatile for reconnaissance surveying or when there are equipment limitations. HGI typically conducts vertical electrical soundings alone or in conjunction with other methods, such as microgravity or induced polarization. Vertical electrical sounding example. Search Search.To browse Academia. Skip to main content.

Log In Sign Up. Papers People. Both approaches are utilized to determine zones vulnerable to groundwater pollution in the Nile Delta. Hence, assessing the nature and degree of risk are important for realizing effective measures toward damage minimization. For DRASTIC indexing, hydroge-ological factors such as depth to aquifer, recharge rate, aquifer media, soil permeability, topography, impact of the vadose zone, and hydraulic conductivity were combined in a geographical information system environment for assessing the aquifer vulnerability.

Additionally, the vulnerable zones identified by both approaches were tested using a local-scale resistivity survey in the form of 1D and 2D resistivity imaging to determine the permeable pathways in the vadose zone. A correlation of 0. This map showed a very high vulnerability zone, a high-vulnerability zone, and moderate-and low-vulnerability zones constituting Identifying where groundwater is more vulnerable to pollution enables more effective protection and management of groundwater resources in vulnerable areas.

Save to Library. This study adopted the measurements of apparent resistivity measured in 40 VES points in the area. VES points were distributed along 6 geoelectric traverses in order to obtain a possible coverage of the studied area. Apparent resistivity measurements were drawn, and their deformations, which resulted from smoothing, were treated. Field curves of VES points were interpreted qualitatively by three procedures to obtain a primary idea about the number of the electrical zones and the depths of the separating surfaces between them, and to map the vertical and horizontal change locations in the apparent resistivity values.

Then the curves were interpreted quantitatively manually by Auxiliary point method and Ebret method to find out the values of quantitative resistivity and thickness of the electrical zones. After that, the sounding curves were interpreted automatically by the computer program IPI2win applying the Inverse manual interpretation method to scrutinize the manual interpretation results and enhance their accuracy if it might be few of their parts by manual interpretation.

The program IPI2win results of interpretation were used to draw 6 Geoelectrical sections along the survey traverses, then they were transferred to geological sections by achieving the proper smoothing, after the matching of the electric zones limits gained from the interpretation process results with the limits of the layers which were penetrated by the drilled wells in the area of study with regard to the effect of the two principle of equivalence and suppression.

Likewise, the results of the interpretation showed that the thickness of the main aquifer of the area is from m and consists of sediments sand, clay sand and clay which belongs to the Injana formation, whose conditions are apt to change in the area, from the confined type to the semi confined, depending on the confining clay layer thickness which bound the aquifer from the top part, and the extent of being affected by folding.

A gravel layer belong to Quaternary sediments mounts the aquifer in middle and south of the study area; a part of this layer is within the water saturated zone in the southern part of the study area, which made in this area a sub-aquifer of the unconfined type with a thickness of about m. Moreover, the geoelectrical sections showed the existence of a high-conductivity layer bounds the aquifer from beneath and was considered as a layer of claystone saturated with saltwater.

Many empirical relations have been put between the geoelectrical parameters, and the Hydraulic parameters by which a Geophysical model was suggested for the aquifer which is supposed to have a constant thickness and varying resistivity and hydraulic conductivity.

These relationships have given several mathematical equations, some of them were used to calculate the hydraulic parameters represented by Hydraulic conductivity and Transmissivity at the electric VES points where no experimental pumping wells were available.

These values were used to draw the two maps of the hydraulic conductivity and the transmissivity for the aquifer. These two maps displayed sites where hydraulic parameters for the aquifer and the areas of low hydraulic parameters rise, so it became possible to new wells locations with high discharge.

Creation the scientific requirements for technical characteristics of equipment for vertical electrical sounding based on the electrophysical characteristics of the soil of energy objects with the different voltage classes


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