*Corresponding Author:Deodonne K, Department of Civil Engineering, National Advanced School of Engineering Yaounde, University of Yaounde 1, Yaounde, Cameroon, France
How to cite this article: Deodonne K, Mbessa M,Gibering N. Geotechnical Characterisation and Valorisation of Lateritic Soils in the Batchenga District
of the Centre Region in Cameroon. Civil Eng Res J. 2021; 11(2): 555810. DOI:10.19080/CERJ.2021.11.555810
The main objective of this study is to contribute to the elaboration of a geotechnical map of the Central Cameroon region through, a geological characterisation of the basement first and, secondly the geo-technical and mechanical characterisation of the laterites of the induced zone with a view to their optimal use in the building and public works sector. For this purpose, a petrographic survey was carried out on a rocky sample and on four material samples identified as OK1, OK2, BA1 and BA2 from two profiles. Geotechnical identification and characterisation tests were done. In addition, mechanical tests were carried out on the Com-pressed Earth Blocks (CEB) and cylindrical specimens made from these materials. The results obtained show several conclusions; The laterites studied are all derived from the alteration of biotite and amphibole gneiss, which is made up of quartz, amphibole, feldspaths, plagioclase, biotite, zircon and opaque minerals; The samples studied have a high sand predominance and are rated as fair to poor pavement materials. The OK1 and BA1 samples belong to class S4 according to the recommendations of CEBTP  and therefore can be used as a form and base layer for traffic class T1. Samples OK2 and BA2 have the characteristics required for the manufacture of bricks.
Foucault and Raoult  define laterites as ferruginous, hardened red tropical soils (especially ferralitic soils). there are residual of detrital soils resulting from the alteration of pre-existing rocks and contain commonly a considerable quantity of iron and aluminum oxides, kaolinite and silica, but small quantities of titanium oxides, manganese, magnesium, etc . The soil type has the characteristics of a hard, impenetrable, and very difficult to change if dry conditions . In tropical areas in general, and in Cameroon in particular, laterites are of great interest because of their abundance, availability and easy workability (Figure 1) [3-7]. These laterites are the most commonly used soils in civil engineering works, particularly in road construction in most countries of intertropical region and in construction buildings, which are the basis of the socio-economic development of most communities. Prior knowledge of the geological, geotechnical and mechanical characteristics of this type of mate-rial throughout the Cameroonian territory for subsequent optimal exploitation in the construction and public works sector (the bearer of development)
is ideal and remains a very worrying activity for Cameroonian researchers [8-13].
The District of Batchenga is all the more attractive for researchers as it is not only a climatic transition zone between forest and savanna but also and above all, it has been chosen as an investment zone within the framework of the emergence of Cameroon in the year 2035. Laterite being a heterogeneous material, it has a complex behaviour. This is why the material must be well identified before any decision is taken with a view to its possible valorisation. The present study proposes to carry out, first, a geological char-acterisation of a rock sample taken from the Nkolmekok quarry and, secondly, a geotechnical and me-chanical characterisation of the surface formations of the Okongolo and Balong localities, all in the Batchenga district, Lékié division in the Central Region of Cameroon, with a view to optimise their use in the civil engineering sector.
Several field works were realised and devoted to lo-calise monitoring sites and sampling. Laboratory tests included identification (Atterberg limits, parti-cle size analysis and methylene blue test) and char-acterisation tests (California Bearing Ratio, Proctor test and mechanical test).
The two sampling points for laterites are located in Okongolo
and Balong respectively, the rock quarry is in Nkolmekock. These
three points have the respective coordinates N04 17’ 36’’ E11
39’ 12’’; N04 16’ 17’’ E11 39’ 23’’; N04 13’ 13’’ E11 35’ 39’’. The
observation of the profiles was done vertically from bottom to
top and consisted in the visual identification of all the levels at
different weathering profiles. The characterisation criteria used
were texture, thickness and mineralogy. Soil samples were taken
using a shovel and pickaxe. The samples were placed in bags
previously labelled with the initials of the name of the study area
(BA) or (OK) followed by the numbers 1 and 2 indicating the level
The petrography of the rock was carried out in two stages
including the realisation of the thin slide at the Institute of
Geological and Mining Research of Cameroon (IRGM) and the
description of this thin slide using a polarizing optical microscope
of Leitz Wetzlar type.
Identification tests and classification
Preliminary tests involve defining the nature of soils using
basis human senses. They are indicated in Table 1.
Atterberg limits, grains size analysis and methylene bleu tests
The Atterberg limits and the particle size analysis are carried
out respectively according to NF P 94-051 , NF EN 933-1 
and NF P 94-057 .
California Bearing Ratio and Proctor tests
The California Bearing Ratio (CBR) and proctor tests are
realized following respectively NF P 94-078  and NF P 94-093
The samples taken were subjected to mechanical tests,
including simple compression according to NF EN 12390-2 ,
traction by splitting according to NF EN 12390-6  and traction
by bending on cylindrical specimens and compressed earth blocks
made up. Cylindrical specimens for compressive and tensile tests
by splitting are obtained by compaction in a CBR mould (Figure
1). While the Compressed Earth Blocks (CEB) for compression
and bending tensile tests are obtained by compacting using a GEO
50 type mould (Figure 2).
The rocky material studied comes from the Nkolmekok
quarry located on the Obala-Batchenga road. This quarry covers
an area of 17.25 ha. The bedrock has a dark grey to light grey
overall appearance and has more or less distinct bedding in some
areas. There are also some elements of biotite and feld-spaths in
sizes ranging from a few mm to cm. The four laterite samples that
were subjected to the study were taken from two distinct profiles
respectively. OK1 and OK2 came respectively from the soft clay
and nodular clay levels of the Okongolo soil profile (Figure 3),
while BA1 and BA2 came respectively from the same levels of the
Balong soil profile (Figure 4).
Identification and classification of studied materials
Rock materials: Petrography
In thin layers, the rock has a heteroganular grano-blastic
texture composed of 25 % quartz, 20% pla-gioclase, 20%
amphibole, 19% biotite and 15% potassium feldspaths (Figure
5). The accessory phase represents 1% and consists of zircon and
opaque minerals. The rock studied is a gneiss with biotite and
amphibole (Figure 5).
Lateritic materials: Plasticity
The consistency of the materials is shown in Table 2 and
Figure 6. It shows that the OK2 and BA2 materials are not very
plastic and can be used for brick making according to the plasticity
diagram of Bain and Highley (Figure 6) [21-23]. However, the
plasticity of a material can be im-proved (Tejiopgap et al., 2003);
Ok1 is moderately plastic while BA1 is very plastic. The projection
of all the samples studied in the Casagrande diagram (Figure 7)
shows that it is a very plastic stringer (Lt) for BA1 and strings (Lp)
and organic soils with little plasticity (Op) for the samples OK1,
OK2 and BA2. The samples studied have a swelling potential of
less than 1.5 and are therefore classified as low-swelling soils as
shown in Table 2.
Grain size distribution
Table 3 shows the values of the different grain size distribution.
Examination of the results in Table 3 shows that the OK2 and BA2
samples have spread curves and are classified as “clay sands” with
traces of silt and gravel for OK2 and with some silt and gravel
for BA2. The fine fraction is 46% and 47% respectively for OK2
and BA2. The sieve size curves for the BA2 and OK2 samples
incorporate the specification spindles for CEB (NC 102-114, 2002-
2006) as shown in Figure 8. These samples can be used for the
production of perforated bricks according to Table 4 because their
grain size fraction below 2 microns is 30% and 25% respectively.
According to Winkler’s diagram (Figure 9), OK2 and BA2 can
be used for the production of dense bricks. The OK1 and BA1
samples have spread curves and are classified as “gravelly sand”
with some clay and silt for OK1 and sandy gravel with some clay
and traces of silt for BA1. The OK1 and BA1 samples show 44 %
and 22 % fines respectively. BA1 can be used as a base course
and foundation course since its grading curve fits in part into the
specification ranges for base and foundation courses as shown in
Figures 10 and 11.
Results obtained from the particle size analysis and Atterberg
limits classifies according to the LPC classification OK1 and OK2
as silty sand, BA1 is a Silty gravel meanwhile BA2 is Clayey sand.
According to the HRB classification; OK1 belongs to class A-7-5
as clayey soil; OK2 to class A-4 as loamy soil; BA1 to class A-2-7
as silty or clayey gravel and sand and BA2 to class A-7-6 as clayey
soil. All these materials are classified as fair to poor for road
Value of Methylene blue
The value of methylene blue found is 11g/110g soil, which
qualifies the materials as at the threshold separating clay soils
from very clay soils, with moderate swelling potential. In addition,
the activity of clay fraction is estimated at 0.61. This value is less
than 0.5 obtained by Ekodeck . According to the norm NF P
94-068 sand belongs to the group of inactive soils, this is due to
the quartz nature of sands .
Characterisation of the materials studied
The curves of dry density versus moisture content are shown
in Figures 12 and 13. From these curves, the value of the optimal
moisture content and the optimal dry density of 18.82% and
2.19 for gravelly sand (OK1) and 18.6% and 2.45 for sandy gravel
(BA1) are deducted respectively. These values are different from
10 % and 2.03 obtained by Ndzié  on the lateritic gravels of
Batchenga. This difference can be explained by the percentage and
nature of the fine particles. OK2 and BA2 have the same maximum
dry density of 1.28 close to the range 1.30 to 1.70 proposed by
Mamba Mpele  for the manufacture of CEB. The optimum
water content of these same materials is of the order of 18.9%.
Figure 14 show the CBR index curves as a function of the dry
density of each material. The figures for OK1 and BA1 show 18 %
and 18.5 % respectively. The CBR index values are lower than the
46% value obtained by Ndzié in 2014 in Batchenga and are higher
than the 6.90% value obtained by Guetcho  in Tiébélé, Burkina
Faso. The difference ob served in the CBR values of the different
samples studied can be explained by the percentage and nature
of the fine particles. According to the CEBTP specifications and
following the table of bearing capacity class, BA1 and OK1 belong
to class S4 to the recommendations of CEBTP  (15< CBR<30)
and can therefore be used as a base and subbase layer for traffic
class T1 Figures 15 and 16. There is a correlation be-tween CBR
value and dry density according to Nkoumou. The same authors
estimate that the CBR of a material increases with its dry density.
The mechanical behaviour of the samples studied shows that the
values for tensile strength by splitting have a similar evolution to
that of compression for OK1 and BA1 (Table 5). They decrease as
the number of curing days increases. The compressive strengths 5
and 5.9 MPa respectively for OK2 and BA2 meet the Cameroonian
standard, which requires that the strength of CEB be greater than
or equal to 4 MPa.
The main objective was to contribute to the elaboration of a
geotechnical map of the region of Central Cameroon through, a
geological characterisation of the basement and, the geotechnical
and mechanical characterisation of laterites of the area raised
with a view to their optimal use in the building and public works
sector. A petrographic study was carried out on a rock sample and
four material samples (OK1, OK2, BA1, BA2) from two profiles
from the geo-technical identification and characterisation tests
were taken. In addition, mechanical tests were carried out on the
BTCs and cylindrical specimens made from these materials. The
results obtained suggest that (l) the OK1 sample is a Limestone
sand belonging to class A-7-5 according to the HRB classification,
its plasticity is 11%, its optimum water content is 18.82% for a
maximum dry density of 2.19 and its CBR is 18%-the compressive
strengths at 4 and 7 days are respectively 3 and 2.6 Bars while the
tensile strengths for the same ages are respectively 1 and 0.7 Bars;
(2) the OK2 sample is a silty sand belonging to class A-4 according
to the HRB classification, its plasticity is 4%, its optimum
water content is 18.9% for a maximum dry density of 1.28 the
compressive and flexural strengths at 14 days are 5 and 0.27 MPa
respectively; (3) the BA1 sample is a silty gravel, belonging to class
A-2-7 according to the HRB classification, its plasticity is 21%, its
optimum water content is 18.6% for a maximum dry density of
2.45 and a CBR of 18.5%-the compressive strength at 4 and 7 days
is 0.6 and 0.2 Bars respectively, while the tensile strength for the
same ages is 1 and 0.7 Bars respectively; (4) sample BA2 is a clayey
sand belonging to class A-7-6 according to the HRB classification,
its plasticity is 7% and its optimum moisture content is 18.95%
for a maximum dry density of 1.28 - the compressive and flexural
strengths at 14 days are 5.9 and 0.3 MPa respectively; (5) The
samples studied have a high sand predominance and are qualified
as fair to poor pavement material. The OK1 and BA1 specimens
be-long to class S4 to the recommendations of CEBTP (1984) and
can therefore be used as a subgrade and sub-base layer for traffic
class T1. Samples OK2 and BA2 have the characteristics required
for the manufacture of bricks
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