The sampling section is the mother section of any laboratory test, that is to say, the section through which all the samples taken from the different sites pass before the test. The samples taken must be representative of the materials that the company needs.

Sampling is the process of obtaining the quantity of materials needed to carry out the tests. Each sample contains a label that constitutes its identity document. Sampling is done in two stages:

Sampling is the operation of taking a quantity of material such that the part taken is representative of the whole material. The sample taken on the site must be spread on a tarpaulin and dried in the open air if it is too wet; the largest elements must be crushed in order to facilitate the drying of the material. Also, the material must not be completely dry to avoid the departure of fines during sieving.

Sampling is done by quartering or using the sampler:

These two operations make it possible to obtain the same results, that is to say, the homogeneity of the material subjected to the test.

Before sampling the GAL or clay, its water content must be checked, and the material must be moistened so as not to lose the fines during sieving. The distribution of points from the GAL and clay is as follows:

The sampling of crushed rock and quartz is done as follows:

1) PURPOSE OF THE TEST

The purpose of the Atterberg limit test is to determine the water content of the soil when it passes from the liquid state to the plastic state of the soil. At the end of this test, it is necessary to determine:

2) PRINCIPLE OF THE TEST

After sampling, the material obtained must be soaked in water in a container at room temperature for 24 hours. The material is then washed with sieve 27 and the wash water (passing sieve 27) obtained is collected in a container and left to settle for 12 hours, after decantation the clear water is siphoned off without touching the solid deposits ( Figure 1 shows what we get). Excess water is evaporated at a temperature not exceeding 50˚C. In fact, the test is carried out in two stages:

3) MATERIALS USED

The equipment used to perform the limit test is:

4) DETERMINATION OF THE LIQUIDITY LIMIT

a) PROCEDURE

The operations described below are to be carried out successively:

$C=\frac{\text{mass passing the 0}\text{.4 mm sieve}}{\text{sample mass}}$(1)

Divide the dough in two using the groove tool. The groove will be made in one movement.

The entire test is repeated 3 to 5 times, varying the water contents either by drying or by adding water, so as to cover a range of blows from 15 to 35.

b) EXPERIMENTATION OF THE LIQUIDITY LIMIT TEST

The previously obtained paste must be used to search for the 5 points. Using the spatula, the paste is homogenized by kneading and then spread in a clean and dry cup to avoid air bubbles. The spread paste is then divided symmetrically with the groove for an opening of approximately 20 mm ( Figure 2 ); the cup is fixed on the metal support of the Casagrande apparatus. Using the cane of the Casagrande apparatus, a series of shocks is actuated at a rate of 2 strokes per second. The shocks require a closure of approximately 1 cm long, or N, the number of shocks necessary for the closure of the 5 points. This closure is included in a series of shocks spaced 4 times apart:

NB: if N is less than 15, the paste is very liquid, so it is necessary to knead to reduce the water content and if N is greater than 35, the paste is too dry, so it is necessary to add a little water and repeat the kneading procedure to homogenize the paste.

Then using the spatula, the material is taken symmetrically at the level of the closure in two capsules or petri dishes of known mass and weighed before being placed in the oven at 105˚C for 4 hours. After the 4 hours, we let the capsules cool and then weighed them. The result obtained makes it possible to determine the water content of each material contained in the different capsules. We average the water content in order to obtain the 5 points for tracing the line, which means it is necessary to have at least 3 points. This line makes it possible to obtain the liquidity limit at 25 strokes.

1) Purpose of the test

The purpose of the test is to determine the weight proportions of grains of different sizes that make up the soil. The percentages thus obtained are expressed in the form of a graph called a granulometric curve.

2) Principle of the test

The test consists of washing a material of known mass with a modulus 19 sieve in order to detach the clay coatings that contain it from the solid grains. Once dried, the material is sieved using a series of sieves and the cumulative rejects are successively weighed on each sieve, allowing us to obtain the passers-by by calculation [5] .

3) MATERIALS USED

The materials used to perform the AG test are:

4) OPERATING MODE

1) Purpose of the test

This is one of the most widely used tests in road geotechnics. The purpose of the Proctor test is to determine, for compaction of a given intensity, the water content (ω optm.) at which the material must be compacted to obtain the maximum dry density (γd max.). The test is carried out according to the French standard NF P 94-095 [6] .

2) Principle of the test

The principle of the test consists of moistening soil with several water contents and compacting it using a process (56 cuts for each layer) and conventional energy. For each of the water content values considered, the dry density of the soil is determined and the curve of variations of this density is established as a function of the water content. Generally speaking, this curve called the Proctor curve presents a maximum value of the dry density (Yd). It is obtained for a particular value of the water content (W). These two values are called the Modified Proctor compaction characteristic values.

3) Test procedure

To perform the test, the mold must be chosen according to the nature of the test to be performed, i.e., the Modified Proctor mold for the Modified Proctor test. Then, the moistened specimens are compacted by introducing the quantity of material so that the height of the first layer after compaction is slightly greater than one-fifth of the height of the Modified Proctor mold. Compact this layer with the PM tamper, applying 56 strokes per layer (5 layers) ( Figure 3 shows the test process).

4) CBR (California Bearing Ratio) bearing test: NF P 94-078 (1997)

Compaction is carried out at a water content corresponding to 95% of the OPM determined during the Proctor test. When the maximum dimension of the soil elements to be studied is less than 20 mm, the entire soil is subjected to the test. If the soil contains elements greater than 20 mm in a proportion of less than 30%, they are eliminated by sieving. The test is then carried out on the remaining fraction. All the CBRs in our study are carried out after imbibition (or immersion). The compacted specimen in the CBR mold is immersed in water for four days, after which punching is carried out. The aim of this operation is to place the soil in the worst hydrometric conditions that it is likely to encounter in practice.

In this section, we will present the results of the identification tests (Granulometric Analysis (by Sieving and Sedimentation), Atterberg Limits, Proctor-CBR Tests, Methylene Blue) of the GAL on which the improvement studies will be carried out. At the end, a summary of the results will be presented in order to give an opinion on the characteristics of the materials studied.

1) RESULTS OF THE GRANULOMETRY ANALYSIS TEST

The Granulometry Analysis by sedimentation is the complement of the Granulometry Analysis by sieving. The curve below is the result of the AG carried out on the raw material of the GAL ( Figure 4 ).

The granulometry curve shows that our material contains more coarse soils (sand, gravel, pebbles) and a small portion of fine.

In order to better see the proportion and nature of the GAL grains, we will summarize the values obtained in the following Table 1 :

These results obtained show that our material actually contains more granular elements than fine elements.

For a good realization of the roads, the CEBTP (1984) proposes the granulometric range within which the curve should be inscribed. In order to know if the material really suits the range proposed by the CEBTP we will make a comparison of the results. In the same way for the percentages of grains at the 80µm sieve, the CEBTP (1984) gives a value between 4% - 20% for the base layer and 5% - 35% for the foundation layer; on the other hand, we have 80 µm = 24.5%. So, from the granulometric point of view, the material can be used in foundation layer without improvement but not in the base layer. So, it must be improved to different percentages in order to use it in the base layer.

2) RESULT OF THE ATTERBERG LIMIT TEST ( Table 2 )

Table 2. The Atterberg limits of the GAL.

These parameters characterize the clayiness of the material; according to the LCPC classification (Central Laboratory of Bridges and Roads) our material has very plastic silt with liquidity limit WL = 62% and IP = 29.5%. The plasticity limit allows us to calculate the plasticity index: I_P = W_L − W_p.

The Atterberg limits are water contents by weight corresponding to particular states of soil. Also, in this parameter, we determine the clayiness of the material through the value of the plasticity index, which must comply with the CEBTP standards for use in a base layer. According to the CEBTP (1984), a base layer material must have an IP of 15. On the other hand, we have an IP (Plasticity Index) equal to 29.5, which means that our material contains a lot of fines. It is in this sense that after analysis of our results, we note that the material is not usable as a base layer, so it must be improved [7] .

3) RESULT OF THE PROCTOR TEST MODIFIED

The Modified Proctor curve gives us a water content W% OPM equal to 19.3 and a dry density Yd equal to 1.79 ( Figure 5 ). The values obtained will be used to mold the CBR.

The results obtained are summarized in Table 3 below:

For the material to be usable as a base layer, the CEBTP gives us an OPM density of at least 2, which is not our case. Also, we have a very low CBR bearing capacity to be used as a base layer, which requires improvement [8] .

4) RESULT OF THE CBR TEST

These values present in Table 4 were calculated by projection on the stress-deformation curve taking into account the F(div) references at 2.5 and 5 from the depression ( Figure 6 ); the CBR Index is therefore the highest value obtained, i.e., 24, 47 and 67 [9] .

The stress-deformation curve allows us to obtain the values of the CBR indices at 10 strokes, 25 strokes and 56 strokes. These values allow us to plot the index-dry density curve.

The index-dry density curve for determining the CBR bearing capacity was plotted from the data of the stress-deformation curve ( Figure 7 ).

The CBR bearing curve shows us the evolution of the CBR bearing capacity from 90% to 98%, allowing us to see if the material can be used in road construction.

Thus, we can say that these values obtained do not meet the CEBTP requirements for a base layer, so it must be improved.

The data from these two (2) curves are summarized in Table 5 below:

Knowing that the CBR molding water is obtained after the Proctor test according to the 56 strokes per layer process, which refers to 56 CBR strokes, we must obtain results similar to 56 CBR strokes or more or less equal to 2. This observation is made in Table 3 and Table 5 .

The obtained bearing capacities do not meet the CEBTP conditions because at 98% a CBR bearing capacity of 80 is required, which is not the case, so it must be improved.

Soil improvement can be explained as changing its properties by using chemicals or physical means to increase its quality. The main objective of soil improvement is to increase its bearing capacity, resistance to weathering and permeability [10] .

Since the quality of materials has a significant influence on the proper functioning of the road, we will improve our material at different dosages of cement and lime. In order to optimally improve the mechanical characteristics of lower bearing materials used in the structure of pavements, we will improve our materials at the following dosages:

Proctor Modifier test: 2%, 4% and 6% and that of CBR at 2%, 4% and 6% according to the recommendation of the laboratory of bridges and roads for the construction of economic and durable pavement layers; the test was carried out at the 100 KN ring [11] .

1) Modified Proctor

Modified Proctor test was conducted to determine the effect of cement and lime on compaction parameters such as maximum dry density and optimum water content ( Figure 8 ). For improvement, the quantity of cement or lime is weighed while considering the improvement rate. The materials are well mixed and covered to avoid an increase or decrease in water content of the materials subjected to Modified Proctor test. The results of water content (W%) and density (Yd) are reported in Table 6 below:

The maximum dry densities of lateritic gravel treated with 2% and 4% lime decrease while the optimum water contents increase. The decrease in maximum dry densities is explained by the fact that the addition of lime to soil causes an agglomeration of its particles, which then occupy large volumes. The increase in optimum water contents, on the other hand, is due to the high demand for water in the materials after the addition of lime and also to the high affinity of lime for water. However, we note an increase in density when improving the material to 4% and 6% lime; this can be explained by a decrease in water content. This decrease is due to the consumption of water necessary for the hydration of lime and the evaporation of water following the hydration reaction, as well as the aeration caused by mixing.

The results obtained show that the addition of cement to BAMA lateritic gravel increases the optimum water content while decreasing the maximum dry density. The evolution of these properties is linked to an increasing affinity of cement for water. Also, the density and water content of cement and lime are generally lower than that of soils. We thus obtain a similar evolution of OPM parameters on lateritic soils treated with cement and lime [12] .

2) CBR TEST

To perform the CBR test, the material must be weighed beforehand while respecting the improvement rate of the cement or lime, just like the PM test. After the CBR test, the material remains in the open air for three days and is immersed for four days, and then, we proceed to punch the molds ( Figure 9 ).

Finally, the CBR curves are plotted for the different samples of laterite improved at 2%, 4% and 6%. The CBR indices were determined at 90%, 95% and 98% of the Optimum Proctor Modified (OPM). The results are recorded in Table 7 below:

The addition of lime or cement to clayey or lateritic soil improves mechanical performance, mainly CBR bearing capacity.

The bearing capacities of the materials increase with the lime content. A similar evolution of the CBR indices according to the percentage of lime treatment is obtained by the cement treatment. The CBR indices of the materials increase with the cement content. This improvement in the bearing capacities would be due to the hydration reactions of the cement and the lime [13] .

The addition of lime or cement to a clayey or lateritic soil increases the optimum water content and consequently the maximum dry density decreases. The increase in the optimum water content is due to the high demand for water after the addition of binders.

The addition of lime or cement to clayey or lateritic soil improves mechanical performance, mainly CBR bearing capacity.

From the bearing capacity point of view, natural samples are suitable materials for the construction of foundation layers. However, their use in the base layer requires improvement. The study of the improvement shows that the material improved with 4% cement has optimal geotechnical characteristics and economic advantages for road construction. On the other hand, with lime, we need 6% lime to have an adequate result for road construction (base layer) [14] .

Economically, it would be preferable to use cement to improve our material.

Research on the quality of local materials is a great challenge that engineers must take care of in order to enhance the materials and obtain standards adapted to our climates. Also, despite the poor quality of the GAL, we have been able to obtain satisfactory results, and perhaps if we deepen the research, we will have results that are in line with our climates.