Triaxial Testing for Geotechnical Design in Swansea & South Wales

A standard CUPP set of three specimens typically takes 5 to 7 working days from the day we receive the undisturbed samples at our Swansea laboratory. Saturation and consolidation phases consume most of that time—low-permeability clays from the glacial till deposits around Swansea require longer consolidation stages to reach full pore pressure equilibrium. CD tests add 3 to 5 additional days due to the slow shearing rate. We can expedite to 4 working days for urgent projects, but this must be arranged before sample delivery so we can reserve a dedicated cell.

For a CUPP test programme on three specimens—the minimum required to define a Mohr-Coulomb envelope—the cost ranges from £1,310 to £2,080 depending on the confining stress range and specimen diameter. This includes sample inspection, trimming, saturation verification, consolidation, shearing, data reduction, and the final report with stress-strain curves, pore pressure plots, and the failure envelope. Multi-stage tests or CD tests with local strain instrumentation fall at the upper end of that range. We provide a fixed quote after reviewing the borehole logs and confirming the testing protocol.

For the stony, overconsolidated glacial till that underlies much of the Swansea uplands, we recommend CUPP tests on 100 mm diameter specimens. The larger specimen size accommodates the coarse fraction—till in this area often contains cobbles up to 20 mm—and the effective stress parameters (c' and φ') extracted from the CUPP are directly applicable to both bearing capacity calculations and settlement analysis under drained conditions. If the till is particularly stiff, with an undrained shear strength above 150 kPa, we may also run a multi-stage CIU test to obtain the strength envelope from a single high-quality sample, which is often all that survives the sampling process in this material.

Yes. A standard CUPP test gives us the stress-strain curve and, from that, the secant Young's modulus at 50% of peak deviator stress (E50). But for finite element or PLAXIS modelling where small-strain stiffness governs, we can instrument the specimen with local Hall effect transducers that measure axial and radial strain directly on the sample, eliminating machine compliance and bedding error. This gives us the true E0 (small-strain stiffness) and the stiffness degradation curve. We have run this configuration on overconsolidated clays from the Swansea Bay area for several deep excavation projects where wall deflection predictions were sensitive to the stiffness input.