The drift geology beneath Stoke-on-Trent presents a real mix of glacial till, sand and gravel pockets, and weathered mudstone from the Upper Carboniferous Coal Measures—sometimes within the same borehole log. We have worked on sites in Hanley and Longton where the SPT N-value jumps from 8 to refusal in less than a metre, reflecting the erratic bedrock surface typical of the Potteries. Standard Penetration Testing remains the most practical way to profile strength variability in these conditions, providing split-spoon samples that our lab in the West Midlands processes for classification and shear strength correlation. When the drift cover is thin and fill layers are encountered, we often combine SPT data with test pits to map anthropogenic material thickness that boreholes alone can miss.
A single SPT refusal at 2.4 m in Stoke-on-Trent can shift a foundation design from pad footings to driven piles—and save the contractor a costly redesign later.
