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Lithostabilisation of Karal: Case of Maroua at
the Far North Region of Cameroon
Mbessa M1* Deodonne K2, and Wansi LMW3
1Department of Civil Engineering, National Advanced School of Public Works, University of Yaounde , Cameroon
2Inspectorate of Pedagogy for Industrial Education, Cameroon
3University of Yaounde 1, Yaounde, Cameroon
Submission: September 17, 2019; Published: December 05, 2019
*Corresponding Author: Mbessa M, Assistant Professor, Department of Civil Engineering, National Advanced School of Public Works, University of Yaounde 1, Yaounde, Cameroon
How to cite this article: Mbessa M, Deodonne K, Wansi LMW. Lithostabilisation of Karal: Case of Maroua at the Far North Region of Cameroon. Civil
Eng Res J. 2019; 9(4): 555766. DOI: 10.19080/CERJ.2019.09.555766
The main objective of this study is to appreciate the swelling/shrinkage fluctuation of the Karal soil from Maroua city in the Far North region in Cameroon by adding sand at different content: 0, 30, 40, 50, 60 and 70%. The study passes through two types of tests named identification tests and characterization tests. The measuring of swelling/shrinkage amplitude was done using a comparator on a specific system conceived at the Laboratory of Building Materials of the National Advanced School of Public Works Yaounde. The results obtained lead to many conclusions:
i) the studied Karal soil is weak lift loamy clay belonging to A-7-6 class according to ASSHTO classification. This result has been already obtained in a previous study.
ii) the swelling/shrinkage phenomenon is observed when the water content starts decreasing and depends on the consistency of the material, because its highest sensitivity is observed when he passes from the hard state to the plastic state.
iii) the stabilizing effect of the sand starts at 40% content while the analysis of swelling/shrinkage fluctuation on the same mixtures at the optimal water content reveal that the smallest dimensional change is observed with 70% sand content mixture.
Clayey soil (vertisols, planosols) are superficial layers less evolved and they are subject to volume variations as they are filled or not with water. Clayey soils are used in various domains and serve as building material, in the manufacturing of works of art and as support of buildings and roads. However, numerous problems of cracks met in buried pipes, pavements, buildings and roads result not only from an excessive loading of the base ground but also from several parameters which are mostly link to the characteristics of the base soil. In Cameroon, we meet clayey soil preferentially in the far north region of Cameroon . In fact, this region is covered in large part by clay soil called “Karal lands” which have been proven to be one of the main causes of the swelling/shrinkage phenomenon [2-6]. Because of their instability, many constructions suffer from cracking due to their argillaceous nature, hence the need to stabilize them to be used in civil engineering. Karal has been the subject of several studies for stabilization [1,7-11] due to their predominance in this part of Cameroon. However, very few studies  address the dimensional variation aspect. The main interest of this work
is to appreciate the dimensional changes of Karal when mixed with various sand contents (0, 30, 40, 50, 60 and 70%) in order to be use in civil engineering constructions.
Several field works were realized and devoted to localizing monitoring sites and sampling. Laboratory tests included identification (Atterberg limits, particle size analysis and methylene blue) and characterization tests (sand equivalent, Proctor and measurement of dimensional change).
Hit points are located at two places; the first on the edge of the town of Maroua going towards Kaélé (Figure 1) and the second at salak near the interna-tional airport Maroua Salak (Figure 2). Materials were collected using parallel tubes and then coated with paraffin at their ends. This process allowed us to have an undisturbed sample that will give us in-formation on the type of soil in situ. Disturbed soil samples were collected using a shovel and a pick-axe. The samples were placed in bags previously la-belled kw followed by numbers 1 and 2 indicating
the site number. As regarding the sand (S1), it is tak-en from
River Sanaga because of the same structure and components as
the one found in the northern part of Cameroon .
Preliminary tests: 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, the particle size analysis and
the methylene blue test are carried out respectively according
to NF P94-051 , NF EN 933-1  and NF P94-057  and
NF EN 933-9 .
Sand equivalent test and the Proctor test: The Sand
equivalent and proctor tests are realized following respectively
NF EN 933-8  and NF P 94-093 .
Measurement of dimensional change: Measurements of
dimensional change were carried out using the method proposed
by the French norm NF P18-427 . Measurements were performed
on swelling clay sample both undisturbed and disturbed
and on mixtures of the same clay with 0%, 30%, 40%, 50%, 60%
and 70% of Sanaga sand.
Preliminary characterization: Preliminary results on
Karal and sand are presented in Table 2.
Plasticity of materials: Results obtained from the Atterberg
limit tests, as presented in Table 3, show that Karal is a high
plas-ticity soil and is classified as Class A-7-6 according to
the AASHTO classification. This material is not so advisable in
road construction because of its fair to poor behaviour in road
construction. It can be use unless it’s ameliorated.
Grain size distribution: Table 4 present the different grains
size content meanwhile Table 5 present rate of grain size in different
mixture. The studied karal is silty clay. This nomenclature is
specific to clay materials in the northern part of Cameroon .
The sand (S1) is of the gravel type as presented in Table 4 with
22 % of gravel. Figures 3 & 4 show the particle size distribution
of the karal sample and sand while Figure 5 shows the particle
size curves of various mixtures.
Value of Methylene blue: The value of methylene blue
found is 11g/110g soil, which qualifies Karal as a material 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
Sand Equivalent: Data used to calculate the sand equivalent
show that the value of the visual sand equivalent is equal to
95.37% and 92.93% at the piston. These values de-scribe sand
as a very clean one.
Proctor: Results of the compaction test are recorded in Table
6, while the dry density curve following specific water content
is shown in Figure 6. This curve deducts the optimum water
content and the optimum dry density value of 13.2% and 1.82
g/cm3 for Kw1 respectively. The optimum proctor values found
are different from those obtained by Simo ; this could be
due to the amount of sand present in the material. The modified
proctor test on different mixtures per-mitted to have curves
shown in Figure 7 where dry density values are represented
on y-axis and water content values on x-axis. The results are
summarised in Table 7. The figure shows that the maximum dry
density increases significantly with the percentage of sand as
the optimal water content decreases. There-fore, the materials
become less and less sensitive to water.
Swelling-shrinkage: Laboratory results allowed the
dimensional change of Karal to be represented by water content
and time (Figure 8) on undisturbed or disturbed soil samples.
The analysis of these results shows that Karal is a highly
sensitive material same as Bana in their work published in 2016,
it is observed just 30 minutes after the start of the test that the
comparator needle reaches 14.2. The shrinkage is progressively
pronounced as the water content decreases and stabilizes after
six (6) hours at the water content of 2.4. Regarding mixtures, the
examination of the curves in Figure 9 shows that the amplitude
of the swelling/shrinkage depends on the water content of the
material. The phenomenon is more accentuated as the water
content is high. The best results are observed for mixtures
containing 70% of sand where the amplitude is then minimal as
shown in Figure 10 and Table 8.
The objective of this work was to study the dimensional
change of karal in order to justify the relevance of its use in
infrastructure works through mixtures of the latter with sand
at various rate based on the results of previous work. Tests
were conducted on natural Karal and sand-stabilized Karal at
per-centages ranging from 10 to 70, including identification
tests such as particle size analysis, Atterberg limits, and
characterization tests such as the modified Proctor test and
comparator swelling/shrinkage measurement on Proctor
Modified samples. The results of these tests show that the Karal
studied is a low-lift, silty clay soil of class A-7-6 according to the
ASHTO classification; the phenomenon of swell-ing-shrinkage
occurs when the water content begins to decrease and depends
on the state of consistency of Karal because its greater sensitivity
is observed at the transition from solid to plastic; the effect of decreasing
the swelling-shrinkage phenomenon by add-ing sand
becomes perceptible from 40% sand. Swell-ing decreases as the
proportion of sand increases. In the specific case, it was minimal
for the value of 70% sand which is the highest percentage value
used. The results obtained from this study are usable in road
construction and in the building. However, the results obtained
in this study do not allow us to understand all the causes of
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