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

Abstract

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.