Geotechnical Interattraction of Granites from Ouaddai Region (East) for Use in Civil Engineering

Achklun and Amgala are located in the North and South of Abéché, region of Ouaddaï (Eastern Chad). In Achklun and Amgala crop out, granites which are cross cut by diaclases and veins.Petrographic investigation of rocks shows that granites are of two types: (1) fine grains biotite granites constituted of quartz, orthoclase, plagioclase biotite andopaque minerals and (2) coarse grains amphibole biotite-granites made up of quartz, orthoclase, plagioclase biotite amphibole and opaque minerals.Structural feature investigated are diaclases and veins. Diaclases are observed in biotite granite and amplibole biotite-granite. They display NE-SW trend direction. Veins are observed in amplibole biotite-granite. They have granitic composition and pegmatitic texture. Veins display NE-SW dominant trend direction. The NE-SW trend direction suggests that their emplacement benefited from diaclase network.Geotechnical studies indicate that fine grains biotite granite is more resistant than amphibole biotite-granite. The resistant may vary from one station to another in the same rock type. This variation is due to mineral composition grain sizes and the intensity of fractures (diaclases).Base on field observations laboratory investigation the present work permitted to select the granite more adapted for various building. © 2019 Elixir All rights reserved. Elixir Civil Engg. 137 (2019) 53938-53942 Civil Engineering Available online at www.elixirpublishers.com (Elixir International Journal) Al-hadj Hamid Zagalo et al./ Elixir Civil Engg. 137 (2019) 53938-53942 53939 Experimentation Geotechnical study was carried out on 8 rock samples flush on the surface. Prior to the geotechnical experiments, the samples were crushed and then sieved to obtain 10/14 mm fraction to determine the mechanical characteristics. The LosAngeles trial was performed according to the prescriptions of standard NF P 18-573 (6). Micro Deval test was determined according to standard NF P 18-572 and that of the dynamic fragmentation was carried out according to standard NF P 18574 (7; 8). The specific density is determined according to NF P 18554 and NF P 18-555 by the liquid pycnometer method (9). Results and Discussions Petrographic study Granites petrographic study in the interesting area was carried out on six (6) samples. The granites of two studied sites are exposed in blocks and slabs on the flanks and at the top of hills (Fig 2a). It arises from this description two types of granite: fine-medium-grained granite and medium-grained and coarse-grained granite. From a microscopic point of view, we have biotite granite and biotite and amphibole granite. The percentage estimation was made using the abacus of the relative proportions of minerals in a rock by Michel Levy (1982) (10). The results obtained are shown in Tables 1 and 2. Mineralogical composition and grain size of the studied area play an important role in rock's resistance. The more the rocks are homogeneous (almost the same minerals and sizes), the more resistant they are and vice versa. Petrography directs a geotechnician to make a good choice on a resistant material. According to recent work (Meng and Pan, 2007 (Tamrakar et al., 2007, quartz is capable of accumulating large amounts of energy of elastic deformation, giving them greater resistance compared to other laminated minerals (mica and clay) (11; 12). Structural study Structural elements observed in the geological formations in the studied area are represented by veins and fractures.Diaclases are observed in biotite and amphibole granite (Fig. 3a) and in biotite granite (Fig. 3b) while veins are observed only in biotite granite (Fig. 3c). Break plane measurements show several directions in both biotite and amphibole granite and in biotite granite. In biotite and amphibole granite (Fig. 3d) there is a main direction NE-SW and a secondary direction N-S. In biotite granite only one major direction oriented NE-SW is observed (Fig.3e). This structural study shows that granites in the studied area are intensely fractured, affecting the geotechnical qualities of these materials. Figure 2. Photography and microphotography of granites in the studied area a) Bulk outcropping and granite slabs on the flanks and at the top of the hills at Achklun. (b) Fine-grained biotite granite flush at Achklun (Abéché-Biltine axis). (c) Bulk outcropping and granite slabs on the flanks and at the top of the hills at Am-Gala. (d) Medium-grained granite flush at Am-Gala (e) microscopy of biotite and amphibole granite. (f) Microphotography of biotite granite. Figure 3. Photography of diaclases (a, b, c) Photography of diaclases in (a) biotite and amphibole granite and (b) biotite granite and vein photography in biotite granite. (d, e, f) Rosace of diaclases in (d) biotite and amphibole granite and (e) biotite granite and (f) rosace of veins in biotite granite. Table 1. Summary of percentages of minerals in the first sector. Designation Quartz Orthose Plagioclase Biotite Blackout