Flexible Pavement

A flexible pavement is a multi-layer road structure — bituminous surfacing over granular or stabilised base and sub-base on a prepared subgrade — that carries traffic loads by distributing the wheel pressure through successive layers so that the stress reaching the subgrade is within its safe bearing capacity. Each layer is stronger than the one below; the structure flexes under load and relies on layer thickness and quality rather than slab flexural strength, so its load-spreading and surface ride depend on every layer performing.

In India it is designed per IRC 37 using a mechanistic-empirical method: design traffic in cumulative standard axles (msa) and the subgrade CBR/resilient modulus determine the layer composition and thicknesses from the IRC 37 catalogue/analysis, with the two governing failure criteria being subgrade rutting (vertical strain on top of the subgrade) and bottom-up fatigue cracking of the bituminous layer (tensile strain at its underside). Good drainage and subgrade preparation are decisive — most premature failures (rutting, cracking, potholing) trace to water ingress, weak subgrade or under-compacted layers rather than the bitumen itself.