Brice Tchakam Kamtchueng

Geotechnical, chemical and mineralogical evaluation of lateritic soils in humid tropical area (Mfou, Central-Cameroon): Implications for road construction

Increased cost associated with the used of high quality materials have led to the need for local soils to be used in civil engineering works. In this paper, geo-chemical approaches coupled with conventional geotechnical techniques has been used to investigate vertical and lateral peculiar engineering index properties (EIP) of micaschist derived soils from Mfou, Central-Cameroon for their uses in road construction. The X-ray diffraction (XRD) analysis conducted on the soils indicated the absence of swelling clays. The main mineral phases were quartz, kaolinite, goethite, magnetite and chlorite. Geo-chemical results show that the investigated soils are “true laterites” made up of 41 wt.% of Fe2O3, 35 wt.% of SiO2, 21 wt.% of Al2O3, 1.17 wt.% of K2O and 0.05 wt.% of CaO. The results of geotechnical tests suggest that the upper clayey layer (UCL) and bottom mottled clayey layer (MCL) of the weathering profiles are poorly graded soils with EIP (fines particles (FP) of 61 and 63%, plasticity index (PI) of 30 and 31%, Californian Bearing Ratio (CBR) at 95% of 21 and 19%), which do not allow their use as raw materials in road construction whereas, intermediate nodular layer (INL) are well graded soils having EIP (FP of 26%, PI of 26% and CBR of 39%) that meet the specification required for sub-base materials for light traffic roads. The relatively high sesquioxyde present in these residual soils may act as cementing agent, thereby making the compacted soils relatively brittle. The direct shear test results show that the soils have high bearing capacity (cohesion of 62 Kpa and 27.2° angle of internal friction) making them to be useful in slope stability and shallow foundation design. The comparison of the studied soils with some lateritic soils in Sub-Saharan Africa indicates that i) genesis and climatic conditions are potentials factors that influence EIP of lateritic soils, ii) lateritic soils developed under semi-arid conditions exhibits EIP better than those developed under tropicaland sub-tropical conditions.

Variation of hydrogeochemical characteristics of water in surface flows, shallow wells, and boreholes in the coastal city of Douala (Cameroon)

ABSTRACT Groundwater is used by 3 million inhabitants in the coastal urban city of Douala, Cameroon, but comprehensive data are too sparse for it to be managed in a sustainable manner. Hence this study aimed to (1) assess the potability of the groundwater; (2) evaluate the spatial variation of groundwater composition; and (3) assess the interaction and recharge mechanisms of different water bodies. Hydrogeochemical tools and methods revealed the following results in the Wouri and Nkappa formations of the Douala basin, which is beneath Douala city: 30% of water samples from hand-dug wells in the shallow Pleistocene alluvium aquifer were saline and highly mineralized. However, water from boreholes in the deeper (49–92 m depth) Palaeocene aquifer was saline-free, less mineralized and potable. Water in the shallow aquifer (0.5–22 m depth) was of Na+-K+-Cl−-NO3− type and not potable due to point source pollution, whereas Ca+-HCO3− unpolluted water dominates in the deeper aquifer. Water in the deep and shallow aquifers indicates the results of preferential flow pass and evaporative recharge, respectively. Possible hydrogeochemical processes include point source pollution, reverse ion exchange, remote recharge areas and mixing of waters with different chemical signatures. EDITOR D. Koutsoyiannis ASSOCIATE EDITOR M.D. Fidelibus