Abstract
A survey using the electrical resistivity and test pit methods is carried out in the Douala subbasin in order to investigate the sub-surface layering and evaluate the thickness of each layer through the variation of the resistivity with the depth. Applying the Schumberger array, a total of 48 vertical electrical sounding is conducted along 8 profiles directed W-E and using traditional method, 25 test pits with depth between 15 and 19 meters are done. Qualitative interpretation is carried out through the resistivity and test pit maps. The test pit maps reveal the presence of the following layers: The first layer of thickness varies from 0.2 to 2.0 m (average of 1.9 m). The thickness of the second layer varies between 0.2 and 4.0 m with an average of 2.8 m. The thickness of the third layer is between 2.0 and 4.0 m with an average of 3.8 m. That of the fourth and fifth layers ranges respectively between 4.0 and 6.0 m (average of 5.4 m) and between 2.0 and 6.0 m with an average of 4.4 m. Isoresistivities maps from resistivities computed for different AB/2 values (1.5; 4.4; 13.5; 19; 27.5; 58 m) are generally characterized by the apparent resistivities which define many domains in function of the AB/2 values. The superficial layer is characterized by electric resistivity values ranging from 720 to 2073 Ωm for AB/2 = 1.5 m and probably represents pedologic materials. For other values of AB/2, resistivity varies from 253 to 32,381 Ωm (AB/2 = 4.4 m), 0.1 to 1838 (AB/2 = 13.2 m) with an average of 341 Ωm, 0.3 to 1608 Ωm (AB/2 = 19 m) with an average of 279 Ωm, 6.4 to 1427 Ωm (AB/2 = 27.5 m) with an average 291 Ωm, and 19.7 to 3555 Ωm (AB/2 = 58 m) with an average of 850 Ωm. These different values of resistivity represent the sedimentary materials.
Highlights
The development of a country or even a region depends among other on the wealth of the subsoil
Applying the Schumberger array, a total of 48 vertical electrical sounding is conducted along 8 profiles directed W-E and using traditional method, 25 test pits with depth between 15 and 19 meters are done
The test pit maps reveal the presence of the following layers: The first layer of thickness varies from 0.2 to 2.0 m
Summary
The development of a country or even a region depends among other on the wealth of the subsoil. Sedimentary basins generally have a more or less complex structure and are sometimes interesting areas for the exploration of deposits. The works of Ngon Ngon et al (2012) have shown that these clays can be used in the manufacture of bricks, stoneware, and tiles, with the exception of pyrite rich clays. The studies conducted by Mbog (2016) focused exclusively on the differentiation of soil clay from the alteration of sedimentary materials, sedimentary clays which are deposits of fine sediments. Despite these works, many shadows remain and require in-depth studies to better understand the mapping of the local and regional structures of this locality. The drillings and pits made so far have not completely crossed the different types of materials (sand, clay and sand stone) to ease the differentiation in depth their limits and geometry of deposit
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