A recent widening project along the Monash Freeway east of Melbourne exposed a recurring challenge: the transition from stiff basalt-derived clays near the surface to softer, compressible silt layers in the old stream channels. Without a rigorous subgrade characterisation, differential settlement would have cracked the new asphalt within two years. Our approach integrates dynamic cone penetrometer traverses with laboratory CBR and ensayo CBR protocols to define the design subgrade modulus for each pavement layer. For corridors where the natural ground shows moisture-sensitive plasticity, we cross-reference with limites Atterberg data to anticipate shrink-swell behaviour under traffic loads.
The transition from basalt clay to stream silt along the Monash corridor demands subgrade characterisation every 200 metres to avoid differential pavement failure.