The experimental studies were carried out on samples of lateritic soils collected from Bweremana (Figure 1) in North Kivu (DRC). The purpose of this study is to determine the geological context of the site, to make soundings on the horizontal profile of the long pedological and grooving on the vertical wall and the

main physical characteristics of the samples taken. For this study, soil sampling is done to determine the physical-mechanical properties of the clay soils of the research area. This requires special attention especially since the accuracy and extrapolation of data depends on obtaining samples that retain their characteristic structures in situ [14].

At the pilot site (Figure 2), 12 soil samples were collected to determine the

physical properties of lateritic soils in the study area. Samples for the determination of natural water content and soil density were collected intact by core sampling. Samples for particle size analysis, Atterberg limits and solid grain density were remoulded.

As a result, systematic sampling points with a regular interval of 40 m × 40 m were adopted in this study. The twelve samples collected were distributed along two N-S oriented lines, equidistant of 40 meters according to the geographical coordinates presented in Table 1.

Some preliminary tests as touch/smell/wash tests gave an apparent classification of the material and its organic content. The bottle test verified the presence of all elements (sand, silt, clay). Cigar and splitting tests allowed us to observe the cohesion of the soil, the proportion and the quality of the clay particles. The study of the physical characteristics of the lateritic soils was carried out on 12 samples collected in Bweremana. The water content of the different samples was determined by the oven drying method, following the experimental standard XP CEN ISO/TS 17892-1, 2005 [15]. The density of the solid grains was determined using the pycnometer, according to the standard NF P 94-054 [16]. The apparent density and the dry density were determined by the cutting kit method according to the NF P 94-053 [17] standard. The wet sieves analysis of the material was carried out by sieving according to the requirements of the NF P 18-560 [18] standard. At the end of the sieving operation, the particles size less than 0.080 mm were collected. Their particle size analysis was carried out by sedimentometry according to the standard NF P 94-057 [19]. The particle size curves were generated with MATLAB software (Appendix 1 MATLAB code). The study of the

consistency of the soils was carried out on the basis of Atterberg limits. The Atterberg limits make it possible to characterize the clayness of a soil, thus determining the remarkable water contents located at the border between the different states (solid, plastic and liquid). The liquidity limit (W_L) was determined using the Casagrande apparatus and the plasticity limit (W_P) using the roller method, in accordance with standard NF P 94-051 [20]. The plasticity index (PI) was evaluated as the difference between the liquid limit and the plastic limit. Finally a classification of the samples soils was done according to the CLRB geotechnical classification system.

The water content values of samples are presented in Table 2.

Table 2 shows that the water content of samples BW-SM-08 and BW-SM-09 varies between 5% and 10%, while samples BW-SM-01, BW-SM-02, BW-SM-04, BW-SM-05, BW-SM-06, BW-SM-07, BW-SM-10 and BW-SM-11 vary between 10% and 15%. As for the samples BW-SM-03 and BW-SM-12, the values of water content are 37.00% and 32.60% respectively. So the water content for all samples varies between 5.40% and 37.00% with an arithmetic mean of 14.94%.

The density characteristics of the studied soils are presented in Table 3.

Table 3 shows that the solid grain density ρs has an arithmetic mean of 2.50 g/cm³. The bulk density ρ ranges from 0.83 to1.35 g/cm³, with an arithmetic mean of 1.13 g/cm³. The dry density ρ_d is in the range of 0.61 to 1.25 g/cm³ with an arithmetic mean of 1.00 g/cm³. These densities indicate that the material studied have a non-negligible degree of deformability.

Completing the wet particle size analysis with the particle size analysis by sedimentometry applied to particles smaller than 0.08 mm according to the AFNOR (2001) [21] standard, we obtained the particle size curves represented on Figures 3-14. These results show that the largest grain size for all the samples is 2 mm.

In general, the distribution of grains for the different materials is given in Table 4.

From this distribution, on the whole we notice that the studied materials are rich in fine particles. Their sieve size curves enter the preferential range (Appendix 2. Grain size range for soil suitable for earth construction) suggested (AFNOR XP P13-901: 2001-10) [22] for the manufacture of Compressed Earth Bricks [23] [24] [25].

The consistency parameters of the studied soils are presented in Table 5.

Table 5 shows that the plasticity index (Ip) of materials BW-SM-01 to BW-SM-12 is between 17.15 and 19.36% with an arithmetic mean of 18.25%. The consistency index (Ic) is between 0.18 and 1.57 with an arithmetic mean of 1.08%, which gives the materials studied a plastic character. Similarly, the liquidity index (Il) is less than zero with an arithmetic average of −0.08, which gives these materials a character of hard plastic consistency.

The diagram on Figure 15 shows that the points of the studied material fall within the preferential plasticity range recommended by the AFNOR (2001) [22] standard for the manufacture of Compressed stabilized Earth Bricks (Appendix 3 Plasticity range indicated for soils used in earth construction).

The liquid limit W_L varies from 31.9% to 40.25% with an arithmetic mean of 34.66%. The plasticity limit W_P ranges from 14.20% to 21.77% with arithmetic mean of 16.41%. The plasticity index of the studied soils varies from 17.15% to 19.36%, with an average of 18.25%. These values of variation agree with the ranges that are indicated in the specification (AFNOR XP P13-901: 2001-10) [22] as indicated in Appendix 3, and in the study made by Laurent GUERIN (1985) [26] where the liquidity limit, the plasticity limit and the plasticity index to be considered must be respectively between 25% and 45%; 10% and 25%; and

7% and 25%, related to recommended material for the manufacture of CSEB.

The quick preliminary (smell) test attested that the sample materials have a poor Organic Matter Content. The particle size curves attested that the 12 samples materials have at least 70% of particles whose size is less than 0.08 millimetres. According to the CLRB Classification System [27], those two parameters indicate that these samples materials are either Clay or Silt. The position of the studied samples in the Casagrande chart found the values of the plasticity index and the liquidity limit, show that the whole material of all the samples are classified as Ap (Plastic Clay Class).