Bulletin of Engineering Geology and the Environment | 2019
Variability of geotechnical parameters of lateritic gravels overlying contrasted metamorphic rocks in a tropical humid area (Cameroon): implications for road construction
Abstract
The variability of the geotechnical properties of lateritic gravels developed on metamorphic rocks from the same clay protolith and of a nearby degree of metamorphism was studied for road construction purposes. Chlorite schist-derived lateritic gravels are more quartzose, more plastic (Plasticity Index PI\u2009=\u200927%) and have a weak Californian bearing ratio (CBR\u2009=\u200950%) compared to those developed on mica schists (PI\u2009=\u200918%, CBR\u2009=\u200962%). The principal components analysis results confirmed by those of agglomerative hierarchical clustering reveal the existence of two groups of materials, the lateritic gravels on chlorite schists (skeleton\u2009=\u200948.27%, mortar\u2009=\u200936.31%, fines\u2009=\u200927.63%, PI\u2009=\u200929%, grading modulus (Gm)\u2009=\u20091.88, maximum dry density (MDD)\u2009=\u20092.00\xa0g/cm3, CBR\u2009=\u200944%) and the mica schist-derived lateritic gravels (skeleton\u2009=\u200934.82%, mortar\u2009=\u200925.45%, fines\u2009=\u200917.90%, PI\u2009=\u200918%, Gm\u2009=\u20092.22, MDD\u2009=\u20092.13\xa0g/cm3, CBR\u2009=\u200965%). Chlorite schist-derived lateritic gravels are mainly characterized by granulometric and plasticity parameters, while those developed on mica schists are characterized by physical and compaction parameters. The mica schist-derived lateritic gravels are usable as sub-base layers for any type of traffic and as base course for low volume traffic. On the other hand, those developed on chlorite schists can be used as a sub-base for any type of traffic and require some treatment prior to a possible use as base layers. The higher the degree of metamorphism of the parental rock, the better the geotechnical properties of the lateritic gravels generated.