Cheltenham sits on a geological boundary. The lower town rests on Lower Lias Clay. The higher ground rises onto Cotswold limestone. Neither substrate behaves predictably under a rigid concrete slab without investigation. The clay shrinks and swells with the seasons. The limestone can hold solution features and soft pockets. A pavement jointed in the wrong place will crack within two winters. Our work starts with the ground. We assess the subgrade reaction modulus and the drainage profile. Then we model the slab for the traffic loading and environmental exposure the A40 feeder routes demand. The CBR road assessment often provides the first useful snapshot of formation strength before we proceed to full rigid pavement analysis.
Designing for the wet condition in Lias Clay prevents the slab failure that a dry-summer CBR value hides.
