Influence of testing apparatus on swelling pressure assessment in clay rocks

This contribution presents a combined experimental and theoretical study on the influence of testing apparatus stiffness on the measurement of swelling pressure in clay rocks. A dedicated experimental setup with calibrated axial and radial stiffness was used to perform swelling tests on Opalinus Clay shale. Results reveal significant discrepancies between axial and radial swelling pressures, attributed not to material anisotropy but to the limited ability of the device to maintain the intended quasi-isochoric conditions. A theoretical model was developed to simulate the coupled behavior of the sample and apparatus, analyzing the experimental trends and investigating the importance of sample geometry and geomaterial stiffness. These findings emphasize the critical role of device characteristics in reliable laboratory determination of swelling pressures, with direct implications for the design of safe underground facilities for energy-related applications