Contractors working on the Severn floodplain know that a standard visual inspection of subgrade can be misleading. The soft Lias Clay that underlies much of Gloucester, coupled with pockets of river terrace gravels, demands a quantitative measure of bearing strength before any pavement design is finalised. The laboratory CBR test provides that number, measuring the resistance of a remoulded sample to a 2.5 mm penetration plunger under strictly controlled moisture conditions. We prepare samples at optimum moisture content from the Proctor curve, then soak them for 96 hours to simulate the worst-case saturated scenario that Gloucester’s high winter water table delivers. This approach aligns directly with BS 5930:2015 and the design principles of Eurocode 7 (BS EN 1997-2:2007), giving your pavement engineer a defensible CBR value for the capping and sub-base layers. For sites where the in-situ density is equally critical, we often pair this with a sand cone density test to confirm that field compaction has achieved the target relative density before the CBR sample is even taken.
A 96-hour soaked CBR value isn't just a number – it's a direct proxy for how your pavement will survive a wet Gloucester winter on the Severn clay.
