Journal of Minerals and Materials Characterization and Engineering, 2013, 1, 363-366
Published Online November 2013 (http://www.scirp.org/journal/jmmce)
http://dx.doi.org/10.4236/jmmce.2013.16056
Open Access JMMCE
Geotechnical and Mineralogical Characterization of Soils
Derived from Schist along Sh ango-Chanchaga Highway,
Minna, Central Nigeria
Salome Hephzibah Waziri1, Abdullahi Idris-Nda1, Irmiya Samson Amoka1*, Yusuf Ishaq 2
1Department of Geology, Federal University of Technology, Minna, Nigeria
2Department of Geology and Mining, Ibrahim Badamasi University, Lapai, Nigeria
Received August 19, 2013; revised October 2, 2013; accepted October 16, 2013
Copyright © 2013 Salome Hephzibah Waziri et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Geotechnical studies were carried out on soils from Shango-Chanchaga highway in Minna, in relation to the petro-
graphic characteristics of the parent rock. Samples were obtained from 5 trial pits at 1 km interval for geotechnical
analysis. The moisture content varies from 35.0% to 58.5%, liquid limit ranges from 29.0% to 43.0%, plastic limit
ranges between 9.0% and 26.5%, while plasticity index ranges from 12.0 to 33.5. The optimum moisture content (OMC)
ranges from 12.0 to 14.0, and California Bearing Ratio (CBR) ranges from 2 to 21. The diffractograms showed that the
dominant minerals were clinochore (Mg,Fe)6(Si,Al)4O10(OH)8, quartz (SiO2), cordierite (Mg2Al4Si5O18Ar0.625), and al-
bite (Na0.98Ca0.02Al1.02Si2.98O18). The results showed that there exists a relationship between the mineral composition, the
texture of the rock, and the geotechnical characteristics of the soil types.
Keywords: Minerals; Petrographic Characteristics; Rock; Soil
1. Introduction
There exists a direct relationship between rock types and
soil types because all soils are derived from rocks by the
process of weathering. Studies on tropically weathered
soils have revealed that the bedrock geology exercises
considerable influence on the distribution and nature of
soils [1]. The character of a soil depends partly on the
parent rock from which it was derived. For example, a
soil developing on weathering granite, will be sandy, as
sand sized particles of quartz and partially weathered
feldspar are released from granite. As time passes, the
partially weathered feldspar grains weather completely
forming fine grained clay minerals. The quartz does not
weather easily, so most resulting young soils have both
sand and clay and perhaps silt in them. Similarly, granite,
with abundant feldspars and micas, will produce clay
when weathered. According to Lundgren [2], clay mi-
nerals which are weathering products of feldspar such as
orthoclase, plagioclase and some micas, when present in
the parent rocks, have a strong influence on the engi-
neering properties of rock from which they are formed.
They are small in size and flaky in shape, and hence, they
accommodate water in their structure.
The engineering properties of lateritic soils, such as
plasticity, compressibility, and swelling/shrinkage poten-
tial, depend on the structure of clay minerals. Shafique et
al. [3] indicated that the mineralogical composition of soil
is responsible for all the engineering properties such as
specific gravity, shear strength, Atterberg limits, petro-
physical properties and soil classification. Since the mi-
neral composition and texture of pre-existing rocks deter-
mine the characteristics of soil formed, the petrographic
characteristics of the rocks can be related to the geote-
chnical characteristics of the soil which are all a function
of the types of soils and their grain size distribution.
Shafique et al. [3] conducted an engineering geological
characterization of Lahore soil, based on geotechnical
testing and mineralogical composition using x-ray dif-
fraction. The use of X-Ray diffraction for mineralogical
characterization of soils had also been demonstrated for
various engineering structures and excavations [4,5].
The aim of this paper is to establish the mineralogical
and geotechnical characteristics of soil in parts of Minna,
Nigeria. The study was carried out along Shango-Chan-
*Corresponding author.

S. H. WAZIRI ET AL. 364
chaga road, which is a dual carriage road on the Minna-
Suleja highway, within latitudes 9˚32'49.6"N to 9˚34'49"N
and longitudes 6˚34'26"E to 6˚36'84.2"E, on the Minna
sheet 164 NE (Figure 1). Minna is one of the fast grow-
ing state headquarters of Nigeria, with active road trans-
port networks linking the Federal Capital Territory and
several other major cities of the country.
2. Geology
The study area falls within the basement complex terrain.
The rock types found are predominantly schists that are
mostly exposed along River Chanchaga. The area mapp-
ed has a generally undulating topography comprising
high hills, valleys, and vegetation made of trees and
shrubs. The highest elevation within the area is situated
in the northeastern part, which is about 294 m above sea
level (Figure 2). The area is drained principally by
Chanchaga River where most of the streams in the area
take their source, resulting in a dendritic drainage pattern.
Most of the streams that drain the area are seasonal.
3. Materials and Methods
An integrated approach was adopted, comprising field
mapping, soil sampling, and laboratory tests for geotech-
nical and mineralogical properties. Standard procedures
recommended by ASTM [6,7] were followed for the de-
termination of the geotechnical properties of the soil
samples. Soil samples were taken from 5 trial pits at the
depth of 1m at 1km interval for geotechnical analysis.
The major properties determined were moisture content,
organic content, grain size analysis, compaction test,
Atterberg limit test and California Bearing Ratio tests.
XRD was used for the mineralogical analysis.
Figure 1. Fact map of chanchaga area, minna, Nigeria.
Figure 2. Relief map of shango-chanchaga area, minna, Ni-
geria.
4. Results and Discussion
Hazen’s formula was used for calculating the permeabi-
lity.
2
10
K
Cd
where, K = Permeability; C = Constant of proportionality
= 0.0116; d10 = Effective grain size % passing at 10%..
The results of the permeability tests are shown in
Table 1. The permeability test conducted using the fall-
ing head permeameter gave a value of 1.04019 × 10−3
cm/s which is equivalent to 0.89872416 m/d. According
to Bouwer [8], the geologic materials with such range of
hydraulic conduction are fine grained clayey material
(Table 2). This also agrees with Braja [9] that geologic
materials with this range of permeability are mostly clay-
ey. Generally, it can be seen from the test results that trial
pits 1 and 5 possess almost the same natural water con-
tent, which ranges from 35.0% to 58.5%. The grading
curve obtained is heterogeneous as it varies from one
trial pit to another.
Atterberg limit test is generally used for soil classi-
fication purpose and for predicting their engineering pro-
perties such as compressibility and plasticity, among
others. As shown in Table 3, the liquid limit varies
between 29.0% and 43.0%, while the plastic limit is be-
tween 9.0% and 26.5%. Values ranging from 12.0 to 33.5
were obtained for the Plasticity Index (PI). A small
plasticity index such as 5% shows that a small change in
moisture content will change the soil from a semi-solid to
a liquid condition; this is an undesirable condition for
foundational material. Such a soil is very sensitive to
moisture (unless the silt and clay content combined is very
low, on the order of less than 20%. A large plasticity
index, such as 20% shows that considerable water can be
added before the soil becomes liquid, and the soil is a
Open Access JMMCE

S. H. WAZIRI ET AL. 365
Table 1. Results of Atterberg limits.
Atterberg Limit
Trial pit Depth (m) Permeability
(mm/s) LL (%) PL (%)PI
1. 1 0.0464 29.2 11.5 17.7
2. 1 0.007424 38.7 26.5 12.2
3. 1 0.0116 43.0 9.0 33.5
4. 1 0.022736 32.7 16.0 16.7
5. 1 1.0469 34.0 17.0 17.0
Table 2. Bouwer’s standard for hydraulic conductivity [8].
Permeability K (m/day) range Material
10−8 - 10−2 Deep clay beds.
0.001 - 0.1 Clay, sand and gravel mixtures (till)
0.01 - 0.2 Clay soils (surface)
0.1 - 1 Loamy soils (surface)
1 - 5 Fine grained sand
5 - 20 Medium grained sand
5 - 100 Sand and gravel mixtures
20 - 100 Coarse grained sand
100 - 1000 Gravel
Table 3. Classification of soil by unified system (USCS)
plasticity chart.
Trial
pit
Liquid
limit (%)
Plasticity
index Symbol Classification
1 29.23 17.7 CL
Inorganic clays, silty clays,
sandy clays.
2 38.7 12.2 CL
Inorganic clays, silty clays,
sandy clays.
3 43.0 33.5 CH
Inorganic clays of high
plasticity, fatty clays
4 32.7 16.7 CL
Inorganic clays, silty clays,
sandy clays.
5 34.0 17.0 CL
Inorganic clays, silty clays,
sandy clays.
desirable foundational material. On the other hand, soils
with very high PI (greater than 35%) may have a high
swell capacity [7].
The study area is underlain by schist, which contains
more than 50% platy and elongated mineral often finely
interleaved with quartz and feldspar (Table 4). Two prin-
cipal petrographic varieties of the schist are recognized:
the fine grained biotite schist and the mediumcoarse
grained hornblende schist. The mineral composition and
texture of rocks influence the soil types, which show
various geotechnical characteristics depending on the
percentage of gravels, sands, silts and clay. The clay
content of the soil which is a direct result of weathering
of feldspar and mica in the rocks is also responsible for
the high plasticity of the soil samples. From the USCS
and unified soil plasticity classification chart [6], it can
be deduced that the samples fall within the range of fine
grained soils with major divisions of silts and clays. The
CBR result (Table 5) shows that the soil samples fall
between poor and good and can be used as sub-grade and
base material.
The cohesion of soil is a general indication of its
strength. The liquid limit test is a general index of cohe-
sion because cohesion has been largely overcome at the
liquid limit. According to Rahn [10], cohesion-fewer
soils, such as sandy soils, have low liquid limits, on the
order of 20%. It can be deduced from the plasticity chart
(using the unified soil classification chart) that the sam-
ples fall within the range of fine grained soils with major
divisions of silts and clays. The plasticity chart plotted
for Trial pits 1, 3, 4 and 5 showed that the soil samples
fall above the “A” line within the region of CL (which is
organic clays of low to medium plasticity, gravelly clay,
sandy clays, silt clays and lean clays), while the trial pit 2
is slightly below the “A” line. Soils with liquid limit
values less than 35% are grouped as low plasticity while
those with values between 35 and 50 are classified as
intermediate plasticity [7].
Table 5 shows the MDD and OMC results. The MDD
value ranges between 1.7 - 2.13 g/cm while the OMC
Table 4. Petrographic analysis of rock samples from Chan-
chaga-Minna.
Mineral
Color in
plane
polarized light
Color in
cross-polar
Diagnostic
feature
% in thin
section
Quartz
(SiO2) Colorless
First order
grey, white
to creamy
Lack of
cleavage,
alteration &
irregular
grains.
30%
Plagioclase
First order
grey to
colorless
brown, green,
light pink,
yellow-green
Multiple
twinning
and albite
twins.
15%
Hornblende
Pale green
to greenish
brown
Green with
brownish,
bluish and
yellowish tints
Elongated
and deformed
crystals;
anhedral
55%
Table 5. Results of compaction and CBR tests.
Compaction CBR Test
Trial
pit
Depth
(m) OMC (%)MDD kg/m Penetration at
2.5 mm
Penetration at
5 mm
1.1 12.4 1.94 1.26 1.47
2.1 12.0 1.84 7.10 9.97
3.1 14.0 1.79 13.4 13.0
4.1 13.0 1.90 8.48 10.6
5.1 12.5 2.13 3.18 20.7
Open Access JMMCE

S. H. WAZIRI ET AL.
Open Access JMMCE
366
ranges from 12.0% to 14.0%. Hunt [11] classified soils
with MDD range between 110 and 130 and OMC values
between 11 and 15 as sand-silt clay mixed with slightly
plastic fines. This indicates a reduction in shear strength
due to high pore pressure without an increase in density
even with an increase in compactive effort. CBR values
range from 2 - 21. A comparison of the results with the
work done by Yoder [12] shows that the soil samples fall
between poor and good and can be used as sub-grade and
base material. CBR values are very important for rating
soils for use in the sub-grade, sub-base and base during
dam construction and road construction.
5. Conclusion and Recommendation
The presence of the sands in the soil accounts for the
high porosity values, while the clay content of the soil
accounts for the cohesiveness and the plasticity of the
soil. The mineral composition of the rocks is responsible
for the types of soils collected. The soils show a variation
in geotechnical characteristics, such as cohesiveness,
porosity, and plasticity. It is recommended that soil with
high moisture content and low CBR values should be
excavated since it is not good for road construction and
replaced with suitable soil. Good drainage systems
should also be provided along the road. Proper investiga-
tion should be carried out before any construction to
avoid failures such as pot-holes and cracks which might
be caused by the clay content.
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