**3. Interpretations**

During Memve'ele dam constructions, geological and geomechanical assessment of quaternary deposits and Ntem Formations have been used to characterize construction and dam foundation materials. It is economically rentable to used construction materials which exist within a relatively short distance of dam site. Interpretation properties on the surface and of measured properties in the borehole logs as mentioned above, display that soil deposits are good to excellent performance in the civil application works [6–9] and thus have been used during Memve'ele dam construction [4]. According to Casagrande scale, soil materials are classified from low plasticity to plasticity and in addition, The coefficient of permeability are higher than those obtained in Kiri dam (from 1.5E−08 to 1.00E−6 m/s [10]) and recommended values of 7.00E−10 to 1.00E−06 m/s. This latter property indicates that soil materials are lesser ability to allow the passage of seeping water if they are use as embankment materials.

The deformation modulus values further indicates the relatively clay contents in the soil deposits. These behaviors indicate that these materials can be used as base layer of dam and also can constituted the transition, cushion and filter materials. The total reserve of soil deposits found near the Memve'ele dam site is 182.39 × 104 m3 and natural sand is to about 30.000 m3 . These values are more important and contribute to reduce costs if these materials have been brought far of site.

Ntem Formation conditions indicate that they are hard qualities in respect to physical properties and good resistance against scouring. The excavated quantity of rock material from the structure foundation is nearly 300 × 104 m3 and it has been used for obtaining crushed aggregate and ripping rap materials for dam construction. However, conditions of site with rocks and alluvial deposits indicate very good and relatively poor geological conditions which can constitute dam foundation materials [11]. Concerning dam foundation, evidence of two dam foundation materials is observed and some requirement needs. The thickness of upper residual soil where is weak in the dam axis can be move to obtain Ntem Formations as foundation materials but where, soil deposit is more thickened, it can be used as also foundation materials. This study has shown that Ntem Formations are fractured and weathered. These site conditions have contributed to improve it in excavating the weathered materials and using vegetable cover and Grouting Intensity Number (GIN) [12] for cover slope and introducing the cement grouting through fractures (**Figure 8**). This method leads to reinforce Ntem Formations and slope stability. Overall dam structure can be fitted on the quaternary soil deposits and Ntem Formations.

#### **Figure 8.**

*(a–c) Display different usages of Ntem formations and quaternary soil deposits; (d and e) amendment of Ntem formations and slope formed by quaternary soil deposits with grouting cement.*
