TOPIC: the soil’s water dynamics. The fact that

TOPIC: SOIL CHARACTERIZATION USING ELECTRICAL RESISTIVITY
METHOD AND GEOTECHNICAL INVESTIGATION AT

INTRODUCTION

Basically, this topic
simply means correlating the geotechnical investigation technique with the
geophysical techniques i.e. electrical resistivity tomography to characterize
the subsurface soil in order to delineate the suitability of the soil for
foundation of structures. Soil is of crucial importance or essential in the Agriculture,
infrastructure and mining sector. Subsurface Soil characterization is
imperative prior to laying any foundation of civil engineering structures and
bridges moreover it is also important when determining the depth of the
bedrock. Advancement in technology have beget the generation of geophysical
methods to tackle the everyday rising problems. Geophysical techniques are said
to be nondestructive or noninvasive therefore they course neither any
disturbance to the soil composition, structure nor the soil’s water dynamics.
The fact that this geophysics technique allows for the mapping of the subsoil
in large reconnaissance surveys makes it of great value in prospecting Mol et
al (2010). It is of great relevance to employ Electrical Resistivity Tomography
for the electrical characterization of the soil, to detect structural
heterogeneity of the soil as well as to provide a clear image of the subsurface
soil Serger et. al (2009. Looking inti physics flow of current in the
subsurface soil indicates that there is a possibility of a relationship between
electrical resistivity and the strength of the soil and this should depend on
parameters like cementation, saturation degree, size of the grains and soil
porosity which control the strength of the soil.

 According to Papadopolous et al (2011)
Electrical resistivity tomography (ERT) is in the list of the highly used
geophysical prospecting technique. In the past it was mostly practiced in
exploration of ground water and underground water Drahor (2006). In recent
times there has been an intensive development in the method to image subsurface
structures hence its applications are practiced in various scopes: the likes of
environmental area and civil. Electrical resistivity tomography uses electrodes
array. The major reason to applying Electrical resistivity tomography is to
deviate from using engineering conventional soil characterization methods such
as UUCT because they are considered to be more expensive, slow and imprecise as
they do not implement complete subsurface structure imaging. Real geological
earth material distribution and imaging of the subsurface to competent layer
depths can be done by geophysical data interpretation. The parameters of
interest 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 resistivity
tomography can be used to monitor water content in the soil or water
infiltration.

 Past researches
indicate that resistivity was used mostly  with the standard penetrating testing (SPT) in
order 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 two
specific sites he was studying. Standard Penetrating Test is geotechnical
investigation method that indicates the geotechnical engineering properties of
the subsurface soil Braga at. el (1999).

GENERAL
DESCRIPTION OF THE STUDY AREA

This research is to be carried at Serowe. Serowe is one
of the promising towns with a population of approximately 60000.This town is
found in the Central district of Botswana. Botswana is basically a landlocked
country in the southern part of Africa. It is said to be developing country.

Figure 1: An
image indicating the location of Serowe on the Map of Botswana

 

 

 

 

Serowe is covered
mostly by the arenosols soil to the west. It is characterized by the gentle
topography. In the eastern and the south eastern region of Serowe the
topography is considered to be lower.

FIGURE 2 : derived from google eBooks

 

The major geomorphic
feature of Serowe is the escarpment which covers the Kalahari axis uplift.
Serowe rivers are ephemeral. Most of the year the rivers are dry. The experience
seasonal rainfall. It has summer intensities followed by dry period of winter. The
climate of Serowe is arid just like other areas in Botswana It comprises of the
savanna vegetation This town falls under the Palapye group. The Palapye group mostly
comprise of Clastic Sedimentary rocks like sandstones which cover over 3500km2
in the Eastern Central district of Botswana. There is also the presence
of some carbonate rocks in the area.

 

 

 

BODY

THE MAIN AIM OF THE
RESEARCH

To characterize the subsurface
soil of the Serowe Stadium using electrical resistivity tomography and geotechnical
investigation 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 INVESTIGATION

The idea of the field
work includes Electrical Resistivity Tomography technique for geoelectrical
investigations in association with geotechnical test which are the Standard
Penetrating Test (SPT) and the Dynamic cone penetrating test which are
specifically for geotechnical investigations. There is also collection of soil
samples for further lab use.

ELECTRICAL RESISTIVITY
TOMOGRAPHY TECHNIQUE

Electrical resistivity tomography is a
two-dimensional (2-D) version in which resistivity changes in vertical path as
well as in horizontal course along the survey line Sayed h (2013). ERT uses an electrode array. Basically, measurements
of Electrical resistivity technique employ the concept of the electrode system
that is considered to be standard which is the four-electrode system. In ERT
measurement a set of electrodes are connected to the instrument called
resistivity meter. These electrodes are positioned along a profile line which
is predefined, the electrodes should have a certain/specific inter-electrode spacing.
For measurements the instrument selects four electrodes automatically and
measure the resistivity, it usually takes some time for it actually obtain or
measure.

Standard Penetrating
Test (SPT)

Standard Penetrating
Test provides information on the soil resistance to penetration and this is
useful in soil strength evaluation in terms of the N-values. According to N
values gives an indication of subsurface relative density. Basically, SPT deals
with driving thick walled standard tube into the earth by blow from slide a
slide hammer with a falling distance as well as a standard weight. When a
sample tube is driven into the ground the number of blows for the penetration
of the tube is recorded. Sum of the number of the blows per centimeter of
correlation is called “the standard penetration resistance” also known as the
N-values.

Dynamic Cone Penetration
Testing (DCPT)

Dynamic cone
penetrating test is a method used in measuring the strength of the soil that in
situ, the location of the horizons and the thickness. A metal cone is
continuously driven into the ground to characterize the behavior of the soil. A
standard amount of force from a hammer is used to drive the cone into the
ground in DCPT method. To determine the relative density of the soil and
properties at that level each blow is used. The hand-portability of the DCPT is
considered to be overwhelming there for it is good to be applied for shallow
testing for example in maintenance or road construction. The soil’s bearing
capacity is correlated with the N-values and resistance in DCPT so that they
can penetrate in terms of the blow numbers per 30 cm of penetration Sudha et al.
(2009).

 

CORRELATION OF
GEOTECHNICAL AND GEOELECTRICAL INVESTIGATION DATA

There is no
typical relationship That exists among the resistivity and N-values. each,
susceptible and robust correlation among the resistivity and N-values, had been
pronounced by way of numerous workers. Braga et al. (1999) determined terrible
exponential cor-relation with a low (0.3) correlation coefficient. He further
argued that the coefficient of correlation may be progressed to 0.7 via
disposing of the top tremendously resistive dry layer. A vulnerable
relationship 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) among
the Transverse resistance and the N-values for subsurface soils in alluvial
formation placed in Uttar Pradesh, India. This relationship became web page
specific and the coefficients of linear courting were associated with the
neighborhood lithology and clay content material. To understand the
relationship among the electrical parameters and N-values one has to look at
the controlling elements accountable for variations of electrical resistivity
and soil strength. In SPT test, the soil energy is defined, following the
manner of IS 6403- (1981) code, in phrases of variety of blows (N-values).

 

 

 

 

 

 

CONCLUSION

Soil characterization
of the subsurface soil is very important prior to make foundation designs for civil
structures or construction. Moreover, Geophysical techniques like Electrical Resistivity
Tomography as well as Geotechnical investigation techniques like Standard Penetrating
Test (SPT) and Dynamic Cone Penetrating Test (DCPT) can be employed for
characterization of the soil. It is very ideal to determine the strength of the
soil using ERT as it is rapid, efficient, effective and very economical in contrast
with the direct in situ methods used to determine strength for civil engineering
use and, thus, is very important. ERT data is integrated with the Geotechnical
investigation techniques like SPT and DCPT to characterize the soil however the
is no clear relationship between the N-values and Resistivity as indicated by numerous
researchers.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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