The CPT rig arrives on a low-loader, its 20-tonne weight enough to push the cone through Stoke-on-Trent's layered drift deposits without losing reaction. In this city, the ground profile rarely follows a textbook sequence. Glacial till sits over Coal Measures mudstone, but in the valleys you find pockets of soft alluvium and laminated clay that can squeeze if the tunnel depth is wrong. Our team deploys the piezocone first, measuring pore pressure response at the cone shoulder, because that data tells you whether a clay will drain or consolidate during excavation. We run dissipation tests at tunnel axis level, and the decay curve gives us the coefficient of consolidation directly, without waiting weeks for lab samples. When we encounter sand lenses, often water-bearing, the friction ratio data from the same push helps identify them before they become a face stability problem. For a city built on six towns, where the geology changes every few hundred metres, this site-specific approach is the only way to design a soft ground tunnel that stays within settlement tolerances.
In Stoke's glacial till and laminated clay sequences, consolidation behaviour governs face pressure selection, and getting the permeability wrong by one order of magnitude changes the settlement prediction entirely.
