Brighton’s geology is dominated by the Upper Cretaceous White Chalk Subgroup, a formation that dictates almost every foundation decision between the seafront and the South Downs. In our experience, the chalk here is rarely uniform; the upper 3 to 5 metres often consist of structureless Grade IV-V putty chalk with solution features and clay-infilled pipes that can punch straight through to more competent Grade II rock. A generic desk study misses these local details. That is precisely why a thorough soil mechanics study must integrate rotary coring with standard penetration tests to map the transition from weathered mantle to intact chalk. Along the coastal strip from Kemptown to Hove, we also encounter raised beach deposits and Coombe Head gravels overlying the chalk, creating a perched water table scenario that complicates shallow foundation design. The combination of marine erosion, former valley infills like the Wellesbourne, and a fluctuating groundwater regime tied to tidal influences means laboratory classification alone is not enough; the mechanical behaviour of each horizon needs to be measured under the specific moisture and density conditions found on site.
The chalk beneath Brighton is not a single material: from putty to intact rock, the strength can vary by a factor of twenty within the first six metres.
