Influence of garnet and micas proportions in metamorphic rocks on laterite formation and variation in their road compaction parameters.

This study demonstrates that some proportions of garnet (Cg) and micas (Cb, Cm) of metamorphic rocks influence the formation of laterites and their road compaction parameters, according to the French Association for Standardization (AFNOR) standard. The mineral content (Cg + Cb + Cm) at 29 % induced the formation of few small size nodules and abundant fines (< 80 μm) up to 61.9 %. High mineral content, about 60 % and 73 %, generated large nodules and few fines (12.0 %-5.9 %) in lateritic gravels. The proportions of fines (%fines) are inversely related to the maximum dry compaction density values γdopm (2.000, 2.420 and 2.460 g/cm3) and bearing capacity CBR at 95 % (36, 62 and 68 %). These CBR values indicate that the resulting lateritic gravels can be used as sub-base for all types of traffic and base or running surface for T1 and T2 traffic. The Multiple Determination Coefficients (MCD) are 0.94 with R2 = 0.88 for γdopm; 0.60 with R2 = 0.36 for ω (%) and 0.93 with R2 = 0.88 for CBR in function of Cg, Cb, Cm and %fines. These statistical results account for a strong influence of metamorphic rocks bearing garnet and micas on compaction parameters and %fines of derived laterites. High Cg and Cb of the parent rock gave better geotechnical properties.