Resilient Modulus of Compacted Granular and Lateritic Materials Used as Base Layers for Flexible Pavements in West Africa

Abstract

The objective of the study is to synthesize resilient modulus data available in Senegal and to propose linear and nonlinear elasticity parameters, which can be used directly for the design of flexible pavements in west Africa. The materials tested are unbound aggregates of basalt and quartzite and gravel lateritic soil from Senegal and Burkina Faso. The Repeated Load Triaxial device is used according to French and American procedures to measure resilient modulus. Different models of the resilient modulus are used to determine the parameters of the nonlinear models and the summary and/or characteristic resilient modulus used in the elastic linear calculation. For the nonlinear calculation, the parameters of the models of Seed et al. (1967), NCHRP (2004) and Boyce (1980) are determined. For the linear elasticity calculation, at the optimum water content and at the dry density of 95% of its maximum value, a maximum modulus of between 300 and 350 MPa is proposed for laterites in the base layer. Values ​​of 220 MPa and 150 MPa are proposed for basalt and quartzite respectively. The moduli obtained are not correlated to the CBR values of the materials. A strong variability in the modulus of laterites is also noted, contrary to the modulus of unbound aggregates. Laterites sometimes have higher modulus than unbound aggregates due to cohesion, but they are more sensitive to water. We recommend that unbound materials (untreated gravels and laterites) be compacted in situ to 97% of the maximum dry density and, for laterite, to the optimal water content -1.5 but also to ensure a good waterproofing and good drainage of the structure. Keywords: Resilient modulus; unbound aggregates; gravel lateritic soil; West Africa.