The triaxial cell sits in our loading frame, a transparent cylinder enclosing a soil specimen trimmed to precise dimensions. Gloucester clay samples arrive in sealed tubes, and the first thing we check is saturation. A back-pressure system forces water into the sample pores while cell pressure increases in step, and we monitor the Skempton B-value until it hits 0.95 or better. Only then does the shear stage begin. The load ram descends at a rate calculated from consolidation data, and the internal load cell records deviator stress while pore pressure transducers track excess pressure that a drained test would dissipate. For a city built on Lias Clay and alluvial gravels of the Severn Vale, these numbers define foundation design. A grain size analysis on the same borehole sample gives us the silt fraction, and knowing that helps interpret triaxial results when drainage paths are short.
An effective stress analysis without triaxial data is just guesswork dressed up as calculation.
