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

This study demonstrates that some proportions of garnet (C_g) and micas (C_b, C_m) 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 (C_g + C_b + C_m) 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 γ_dopm (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 γ_dopm; 0.60 with R² = 0.36 for ω (%) and 0.93 with R² = 0.88 for CBR in function of C_g, C_b, C_m 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 C_g and C_b of the parent rock gave better geotechnical properties.