- The clay samples are taken from Togblécopé, a suburb located in northern area of Lomé, the capital town of Togo, about 20 km far from the downtown (Figure 2). The Togblécopé’s soil is a depression of the Zio River, made up of a metamorphic complex that is rich in basic minerals. This complex contains metamorphic rocks that are rich in amphibole and are derivatives of gneiss.

The coastal basin (Maastrichtian to Holocene) stretches up to Tsévié and Tabligbo and consequently covers all over this suburb. This basin is composed of sand, clay, limestone and phosphate [6] .

- The CPJ 35 cement manufactured by CIMTOGO and delivered in bags of 50 kg and the lime of the brand CALVIVA, delivered in bags of 25 kg are taken as samples in a commercial store of Lomé in Togo.

- Silty sand and siliceous sand (sea sand) for stabilization, are taken respectively at Dalavé, 35 km in northern area of Lomé on Togo’s littoral in Lomé (Figure 2)

- For different tests the following material is used: manual shaker; mechanical diving shaker with a speed equal to 10,000 tr/mn of the brand MATEST with a vessel; torpedo densimeter with range 0.995 to 1.035; tubes of brand CHEKAMAT and capacity of 2500 ml; consolidation device; oedometric cell of brand S272-01, serial number S272-01/AC/0007; piston of oedometric system; comparator at 1/100 mm; Casagrand device with cup of the brand LABOTEST and serial number Z10248; groover; dryer of the brand Air-Expert with maximal temperature 160˚C; a pycnometer of minimal volume of 500 cm³ with roded top; a precision scale of the brand METTLER TOLEDO with a maximal capacity of 5 g and a precision of 0.1 g; a sieve system AFNOR.

The tests are carried out in the laboratory Lab-TP (Laboratory of Public Works) of Lomé in Togo.

Samples of reorganized or intact clayed soil are taken from 1 m, 2 m, and 3 m deep well on the soil of Togblécopé.

The stabilization of the clay from different depths is performed with cement, lime, sea sand and silty sand by proportions of 0% to 10% and at paces of 2% of the material mass.

Physical tests (density, limits of liquidity WL and plasticity WP, equivalent of sand ES and granulometries by sieving and sedimentation) are then carried out on such different materials as clay, sands and on mixtures according to standards [7] [8] [9] .

The free swelling is measured with oedometer on samples subject to the only weight of 1080.22 g of piston (Figure 3). The preparation procedure of samples is the following (Figure 4) [10] :

- Saturation of porous stones for at least 1 hour in a water pit;

- Laying of a porous stone at the base with filter paper;

- Laying of sample of soil cut up in the ring on the basic porous stone;

- Laying of a filter paper on the surface of the sample;

- Laying of the second porous stone and blocking of the whole;

- Positioning of the cell on its plate;

- Filling of the tank with distilled water for the saturation.

The variation of the height of the sample is measured according to the duration of application of the charge (12, 24, 48, 60, 120, 240, 480, 900, 1800, 3600,

7200, 14,400, 21,600, 28,800 in s) until it stabilizes. The sample is considered stable when the difference of reading between two successive times does not exceed 0.001 mm.

The reduction in final swelling Rg(%) is given by:

R g = Δ G G 0 = G 0 − G a G 0 (1)

With Rg the relative reduction in final swelling; G_o the reduction in the swelling of pure clay; G_a the reduction in the swelling of stabilized clay.

The results of physical tests on the sand and clay materials are given in Table 1 and Figure 5 and Figure 6.

Table 1 and Figure 5 and Figure 6 show that:

- Dalavé’s silty sand has an extended granulometry with a big proportion of sieved sands 0.08 mm of 20.60% with a module of fineness of 1.39 and an equivalent sand of 55. It falls then under the category of very fine sands [11] ;

- the sea sand doesn’t contain components that are below 0.160 mm; It has a module of fineness of 2.52 and an equivalent sand of 97.5. This sand is then of medium-sized granulometry [12] [13] ;

- the sieved sample sands of 0.08 mm taken at 1 m, 2 m, and 3 m, are respectively of 75.53%, 82.64% and 76.71%. These values are much higher than 50%; the clayed materials from Togblécopé contain then a large proportion of fine grains. Besides, absolute densities of 1 m, 2 m, and 3 m deep can be observed with respectively 2.50, 2.53, 2.54 and indexes of plasticity (Ip) of 25.24,

34.09 and 41.73. The samples taken at 1 m and 2 m deep can then be considered as plastic whereas those taken at 3 m deep are very plastic. The soils of Togblécopé are therefore more and more plastic and dense in depth than on the surface. This Togblécopé’s soil is an instable land composed of swelling clay.

The results of the average of the limit of liquidity and densities of different composite samples (clays, stabilizers) of different depths are shown in Figure 7 and Figure 8.

By examining Figure 7 and Figure 8 the following can be noticed:

- a rise in limits of liquidity and plasticity as the proportion stabilizer increases (Figure 7(a) and Figure 7(b));

- a reduction in the index value of plasticity while the percentage of stabilizer grows (Figure 7(c)); its reduction accelerates depending on whether the sand is thicker (Figure 7(c));

- the stabilization with hydraulic binders (lime and cement), presents densities that grow with their dosages; however, densities decrease with the rise in the proportion of sands (Figure 8);

- cement makes clay denser than lime; the density is lower in the case of stabilization with the sea sand than that of silty sand (Figure 8).

Figure 9 to Figure 13 show the averages of results of different depths, reductions in swellings of different stabilizers.

Figure 9 to Figure 13 show that:

- in average 62% of the reduction in the potential of swelling occurs after 30 minutes for the hydraulic binders whereas it is 32% for sands. After 2 hours, 97% of the reduction in swelling occurs for the binders and 89% for the sands. After 8 hours, 100% of the potential of swelling occurs. The equations of levelling of results of proportion of stabilizer of 10%, providing the highest reduction, are shown in (Figure 11):

R g c i m t = 8.717 ln ( t ) − 14.22 and R 2 = 0.921     if   t < 4986 (2a)

R g c i m t = 60     if   t > 4986 (2b)

R g c h t = 9.832 ln ( t ) − 23.79 and R 2 = 0.935     if   t < 5025 (2c)

R g c h t = 60     if   t > 5025 (2d)

R g s m t = 4.435 ln ( t ) − 14.41 and R 2 = 0.975     if   t < 19200 (2e)

R g s m t = 29.33     if   t > 19200 (2f)

R g s s t = 2.877 ln ( t ) − 6.977 and R 2 = 0.958     if   t < 11800 (2g)

R g s s t = 20     if   t < 11800 (2h)

R_gcimt, R_gcht, R_gsmt and R_gsst are respectively reduction in swelling for such additional components as cement, lime, sea sand and silty sand with t the time in s.

- for 10% of stabilizers the four additional components largely reduced the potential of swelling up to 60% for cement and lime, 30% for sea sand and 20% for silty sand (Figure 11);

- The reduction in swelling goes up with the rise in the proportion of stabilizer (Figure 12); the equations of levelling from these results are the following:

R g c i m T = − 0.883 T 2 + 15.09 T − 2.881 and R 2 = 0.952 (3a)

R g c h T = − 0.837 T 2 + 14.69 T − 3.297 and R 2 = 0.949 (3b)

R g s m T = − 0.125 T 2 + 4.197 T + 0.428 and R 2 = 0.988 (3c)

R g s s T = − 0.180 T 2 + 3.829 T + 0.011 and R 2 = 0.983 (cd)

R_gcimT, R_gchT, R_gsmT and R_gssT are respectively reduction in swelling for such additional components as cement, lime, sea sand and silty sand with T the proportion of stabilizer in %.

- for 4% of the proportion of lime and cement, the reduction in swelling is very pronounced; from 8% of all the stabilizers, the reduction in the potential of swelling stabilizes (Figure 12);

- the swelling is more reduced with the hydraulic binders than that of sand; it is also more pronounced for the stabilizer sea sand than that of silty sand (Figures 10-12);

- the potential of reduction in swelling increases with the limits of liquidity and plasticity, it also rises with the index of plasticity (Figure 13); thus, the more plastic the material the more the reduction in swelling is reduced.