TOPIC: SOIL CHARACTERIZATION USING ELECTRICAL RESISTIVITYMETHOD AND GEOTECHNICAL INVESTIGATION ATINTRODUCTIONBasically, this topicsimply means correlating the geotechnical investigation technique with thegeophysical techniques i.e. electrical resistivity tomography to characterizethe subsurface soil in order to delineate the suitability of the soil forfoundation of structures. Soil is of crucial importance or essential in the Agriculture,infrastructure and mining sector. Subsurface Soil characterization isimperative prior to laying any foundation of civil engineering structures andbridges moreover it is also important when determining the depth of thebedrock. Advancement in technology have beget the generation of geophysicalmethods to tackle the everyday rising problems. Geophysical techniques are saidto be nondestructive or noninvasive therefore they course neither anydisturbance to the soil composition, structure nor the soil’s water dynamics.
The fact that this geophysics technique allows for the mapping of the subsoilin large reconnaissance surveys makes it of great value in prospecting Mol etal (2010). It is of great relevance to employ Electrical Resistivity Tomographyfor the electrical characterization of the soil, to detect structuralheterogeneity of the soil as well as to provide a clear image of the subsurfacesoil Serger et. al (2009.
Looking inti physics flow of current in thesubsurface soil indicates that there is a possibility of a relationship betweenelectrical resistivity and the strength of the soil and this should depend onparameters like cementation, saturation degree, size of the grains and soilporosity which control the strength of the soil. According to Papadopolous et al (2011)Electrical resistivity tomography (ERT) is in the list of the highly usedgeophysical prospecting technique. In the past it was mostly practiced inexploration of ground water and underground water Drahor (2006).
In recenttimes there has been an intensive development in the method to image subsurfacestructures hence its applications are practiced in various scopes: the likes ofenvironmental area and civil. Electrical resistivity tomography uses electrodesarray. The major reason to applying Electrical resistivity tomography is todeviate from using engineering conventional soil characterization methods suchas UUCT because they are considered to be more expensive, slow and imprecise asthey do not implement complete subsurface structure imaging.
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Real geologicalearth material distribution and imaging of the subsurface to competent layerdepths can be done by geophysical data interpretation. The parameters ofinterest in soil characterization includes: the bulk density, water content,carbon content, soil texture and horizonationation. Benson et al (2004)emphasized that the bulk density changes with soil electrical resistivity.Furthermore, Michot et al (2003) indicated that electrical resistivitytomography can be used to monitor water content in the soil or waterinfiltration. Past researchesindicate that resistivity was used mostly with the standard penetrating testing (SPT) inorder to characterize the subsurface soil. On the other hand, Sudha et al (2009)combined Electrical Resistivity Tomography ERT with Standard Penetrating Test (SPT)and Dynamic Cone Penetration Test DCPT for geotechnical investigation of twospecific sites he was studying. Standard Penetrating Test is geotechnicalinvestigation method that indicates the geotechnical engineering properties ofthe subsurface soil Braga at.
el (1999).GENERALDESCRIPTION OF THE STUDY AREAThis research is to be carried at Serowe. Serowe is oneof the promising towns with a population of approximately 60000.
This town isfound in the Central district of Botswana. Botswana is basically a landlockedcountry in the southern part of Africa. It is said to be developing country.Figure 1: Animage indicating the location of Serowe on the Map of Botswana Serowe is coveredmostly by the arenosols soil to the west. It is characterized by the gentletopography.
In the eastern and the south eastern region of Serowe thetopography is considered to be lower.FIGURE 2 : derived from google eBooks The major geomorphicfeature of Serowe is the escarpment which covers the Kalahari axis uplift.Serowe rivers are ephemeral. Most of the year the rivers are dry. The experienceseasonal rainfall.
It has summer intensities followed by dry period of winter. Theclimate of Serowe is arid just like other areas in Botswana It comprises of thesavanna vegetation This town falls under the Palapye group. The Palapye group mostlycomprise of Clastic Sedimentary rocks like sandstones which cover over 3500km2in the Eastern Central district of Botswana. There is also the presenceof some carbonate rocks in the area. BODYTHE MAIN AIM OF THERESEARCH To characterize the subsurfacesoil of the Serowe Stadium using electrical resistivity tomography and geotechnicalinvestigation to understand the reason behind the Serowe stadium’s frequent collapsing. SPECIFIC OBJECTIVES Determining the nature and strength of the soil To find the relationship between resistivity and N-values Examine aggregate structures FIELD INVESTIGATIONThe idea of the fieldwork includes Electrical Resistivity Tomography technique for geoelectricalinvestigations in association with geotechnical test which are the StandardPenetrating Test (SPT) and the Dynamic cone penetrating test which arespecifically for geotechnical investigations.
There is also collection of soilsamples for further lab use.ELECTRICAL RESISTIVITYTOMOGRAPHY TECHNIQUEElectrical resistivity tomography is atwo-dimensional (2-D) version in which resistivity changes in vertical path aswell as in horizontal course along the survey line Sayed h (2013). ERT uses an electrode array. Basically, measurementsof Electrical resistivity technique employ the concept of the electrode systemthat is considered to be standard which is the four-electrode system. In ERTmeasurement a set of electrodes are connected to the instrument calledresistivity meter. These electrodes are positioned along a profile line whichis predefined, the electrodes should have a certain/specific inter-electrode spacing.For measurements the instrument selects four electrodes automatically andmeasure the resistivity, it usually takes some time for it actually obtain ormeasure.
Standard PenetratingTest (SPT)Standard PenetratingTest provides information on the soil resistance to penetration and this isuseful in soil strength evaluation in terms of the N-values. According to Nvalues gives an indication of subsurface relative density. Basically, SPT dealswith driving thick walled standard tube into the earth by blow from slide aslide hammer with a falling distance as well as a standard weight.
When asample tube is driven into the ground the number of blows for the penetrationof the tube is recorded. Sum of the number of the blows per centimeter ofcorrelation is called “the standard penetration resistance” also known as theN-values.Dynamic Cone PenetrationTesting (DCPT)Dynamic conepenetrating test is a method used in measuring the strength of the soil that insitu, the location of the horizons and the thickness. A metal cone iscontinuously driven into the ground to characterize the behavior of the soil. Astandard amount of force from a hammer is used to drive the cone into theground in DCPT method. To determine the relative density of the soil andproperties at that level each blow is used. The hand-portability of the DCPT isconsidered to be overwhelming there for it is good to be applied for shallowtesting for example in maintenance or road construction. The soil’s bearingcapacity is correlated with the N-values and resistance in DCPT so that theycan penetrate in terms of the blow numbers per 30 cm of penetration Sudha et al.
(2009). CORRELATION OFGEOTECHNICAL AND GEOELECTRICAL INVESTIGATION DATA There is notypical relationship That exists among the resistivity and N-values. each,susceptible and robust correlation among the resistivity and N-values, had beenpronounced by way of numerous workers. Braga et al. (1999) determined terribleexponential cor-relation with a low (0.3) correlation coefficient. He furtherargued that the coefficient of correlation may be progressed to 0.
7 viadisposing of the top tremendously resistive dry layer. A vulnerablerelationship has additionally been suggested through Akinlabi and Adeyemi(2014). A fine linear relation-deliver was determined by means of Hatta et al.
(2015). A linear courting has also been acquired by using Sudha et al. (2009) amongthe Transverse resistance and the N-values for subsurface soils in alluvialformation placed in Uttar Pradesh, India. This relationship became web pagespecific and the coefficients of linear courting were associated with theneighborhood lithology and clay content material. To understand therelationship among the electrical parameters and N-values one has to look atthe controlling elements accountable for variations of electrical resistivityand soil strength. In SPT test, the soil energy is defined, following themanner of IS 6403- (1981) code, in phrases of variety of blows (N-values).
CONCLUSION Soil characterizationof the subsurface soil is very important prior to make foundation designs for civilstructures or construction. Moreover, Geophysical techniques like Electrical ResistivityTomography as well as Geotechnical investigation techniques like Standard PenetratingTest (SPT) and Dynamic Cone Penetrating Test (DCPT) can be employed forcharacterization of the soil. It is very ideal to determine the strength of thesoil using ERT as it is rapid, efficient, effective and very economical in contrastwith the direct in situ methods used to determine strength for civil engineeringuse and, thus, is very important. ERT data is integrated with the Geotechnicalinvestigation techniques like SPT and DCPT to characterize the soil however theis no clear relationship between the N-values and Resistivity as indicated by numerousresearchers. REFERENCES A, B. & Cousin I, S.
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