Reinforcement of Flexible Pavements by the Use
of Geogrid: Case of the Road Mbalmayo - Ebolowa
Madjadoumbaye Jérémie* and Camela Woumbe Romario
Département de Génie Civil, Ecole Nationale Supérieure des Travaux Publics, France
Submission: July 01, 2019; Published: July 19, 2019
*Corresponding Author: Madjadoumbaye Jérémie, Département de Génie Civil, Ecole Nationale Supérieure des Travaux Publics, France
How to cite this article: Madjadoumbaye J, Camela W R. Reinforcement of Flexible Pavements by the Use of Geogrid: Case of the Road Mbalmayo - Ebolowa. Civil Eng Res J. 2019; 8(5): 555748. DOI: 10.19080/CERJ.2019.08.555748
The insufficiency of load-bearing capacity of a flexible pavement in service is generally caused by a significant increase in traffic. The consequence of this insufficiency is the appearance of severe damage to the surface layer. Therefore, this pavement must be reinforced with new layers. However, in view of the high costs of pavement materials, more economical reinforcement techniques must be developed. The purpose of this work is therefore to use geogrid to reinforce the new pavement of the approximately 104km long Mbalmayo-Ebolowa road section. The methodology used consisted in determining the layer thicknesses of the new pavement without geogrid, and then with geogrid. Then a comparative analysis of the costs of the two approaches was made. Using Alizé software, we therefore designed the new pavement structure for the sections to be rehabilitated, which have a total length of approximately 63.7km. Then, we determined the nature, characteristics and location of the geogrid to be used. MacREAD software allowed us to analyze the reinforced pavement and determine the final layer thicknesses. As a result, the MacGrid EG geogrid manufactured by MACCAFERRI was introduced into the base layer and reduced the required bituminous gravel thickness by 6cm. A comparative cost study showed us that the solution we proposed saved FCFA 2.3 billion, or about 36 million gains per kilometer..
Keywords: Pavement; Reinforcement; Geogrid
Abbrevations: AC: Asphalt Concrete; BTB: Bituminous Treated Base; SETRA: Service d’Etudes Techniques des Routes et Autoroutes
Road infrastructure plays a fundamental role in the development process of a country. More precisely, they are one of the pivots of economic activity, strategic operations and accessibility to public services. Cameroon, in search of emergence, must nowadays face the multiple problems that its road heritage faces. On the one hand, new roads must be built that will not only be suitable for the ever-increasing volume of traffic on most of the country’s major roads, but also ensure the excellent mobility desired by users and essential for the economy’s development. On the other hand, it is necessary to look at existing roads, whose deplorable condition is an obstacle to development.
Indeed, several road infrastructures in Cameroon are degraded, both in urban and rural areas. This poor road condition not only puts users at risk, but also disrupts traffic, thereby hindering the development of economic activity. Faced with this problem, Cameroon’s road network managers are undertaking maintenance work, or even pavement reinforcement work, in order to eliminate pathologies and restore the pavement to the
desired level of service. For example, the heavy maintenance
project for the road section between Mbalmayo and Ebolowa has been undertaken. This 104km long section has become almost impassable because of the degradations it has suffered. These degradations are the result of a lack of load-bearing capacity of the structure due to an explosion in the volume of traffic on the road. But faced with the exorbitant cost of road materials, we are now forced to look for more economical construction techniques. The general objective of this article is to provide a less expensive method of flexible pavement reinforcement using a geogrid. This work begins with the presentation of the characteristics of the initial pavement and the available materials. Then, we will design the new pavement in a first one without geogrid, and then with geogrid. A comparative cost analysis between the two approaches will be done at the end./p>
The Mbalmayo-Ebolowa section is approximately 104km long with a 7m wide pavement (but the sections to be rehabilitated are 63.7km long). This pavement is now subject to very heavy traffic, class To according to the classification of the Service d’Etudes Techniques des Routes et Autoroutes .The pavement is degraded throughout and along its entire route,
with the exception of recently rehabilitated sections. The project
therefore consists in making a new pavement that will be able
to withstand current and future traffic. Table 1 presents the
characteristics of the pavement materials in place.
The materials of the existing pavement and base layer will
be recycled to form the base layer of the new pavement. The old
sub-base (lateritic gravel) will be considered as the new support
platform. The new base layer will be made of Bituminous
Treated Base (BTB) and the new wearing course will be made of
Asphalt Concrete (AC). Table 2 presents the characteristics of the
materials to be used for the new pavement.
The input parameters for calculating the permissible
values are presented in Table 3. These parameters were
determined using the project data and the guide Conception De
Dimensionnement Des Structures De Chaussée .
The thicknesses of the wearing course and sub-base are
fixed. The only thickness to be calculated is that of the base
layer. The calculation will be done by incrementing the thickness
of the base layer (BTB) from 10cm which is its minimum
implementation value according to SETRA. The incrementation
is completed when the deformations obtained are lower than the
permissible values. Table 4 presents the parameters for defining
the layers in Alizé.
Figure 1, Figure 2 show the results of the calculation of
the permissible values and thicknesses of the pavement layers
respectively. According to these results, the admissible values
obtained are 86.4μ (at the base of the asphalt concrete layer), 80μ
(at the base of the BTB layer) and 326.5μ (at the surface of the
subgrade soil and untreated layers).According to these results,the horizontal deformation at the base of the wearing course, the
horizontal deformation at the base of the base course and the
vertical deformation at the surface of the untreated layers and
the subgrade are 10.6μ, 78.3μ and 241.1μ respectively. These
values are then lower than the corresponding admissible values.
The structure is therefore checked. The thickness of the base
layer then required is 20cm.
The MacGrid EG 30S geogrid manufactured by MACCAFERRI
will be used to reinforce the base layer, which is made of
bituminous gravel. The numerical simulation will be carried out
by the MacREAD software designed by the same company for
the design of pavements with geogrid reinforcement. The sizing
method used by MacREAD is the American AASHTO method.
Since the results given by MacREAD also include the results of
calculations of the structure without geogrid, we will just make
sure that these results are the same as those obtained by Alizé.
The input parameters for the calculation are given in Table
4. These parameters were determined using project data and
the Guide for design of pavement structures . It should be
noted that the characteristics of the MacGrid EG 30S geogrid are
already defined in the MacREAD software.
Figure 3 shows the results of the calculation of the geogrid
reinforced structure. These results show that the geogrid
has reduced the required thickness of the base layer from
20cm to 13.48cm, which will be rounded to 15cm to facilitate
implementation. That is a reduction of 5cm.
Based on the results of the cost analysis, we see that using
geogrid in the base layer is a great economical technique. We
therefore recommend the use of this product in future projects.
Note that the manufacturer of the geogrid used recommends
that it be used only in granular layers [4-5].
During this work we clearly demonstrated by numerical
modelling that the problem of high cost of pavement materials
can be alleviated by the use of geogrids to reinforce granular
layers. The project that we used as a case study is the
reinforcement of the Mbalmayo - Ebolowa road section, whose
total length of the sections to be reinforced was 63km. We have
shown that the use of the MacGrid EG 30S geogrid in the base
layer reduces the required bituminous gravel thickness by 6cm.
This corresponds to savings of more than FCFA 2.3 billion, or
about FCFA 36 million in gains per kilometer.