A contractor recently poured a floor slab on a brownfield site off Hessle Road without first checking the soil’s moisture‑suction state. Within six months the slab had cracked along a polygonal pattern — classic desiccation‑shrinkage. Unsaturated soil analysis would have caught the high matric suction in the laminated clays before the concrete was placed. Hull sits on glacial till over laminated Humber alluvium; these soils exhibit strong unsaturated behaviour that dry‑unit‑weight tests alone cannot capture. Ignoring the suction regime leads to differential movements that no slab thickness can fix. We routinely couple suction‑profile measurements with calicatas exploratorias to expose the actual moisture gradient, then interpret the data under BS 5930 and Eurocode 7 principles.
Suction gradients of 120 kPa per metre in Hull alluvium — unsaturated analysis prevents slab‑cracking and over‑design of foundations.