A new hollow cylinder triaxial cell to study the behavior of geo-materials with low permeability

Abstract : A new hollow cylinder triaxial cell (60 mm internal diameter and 100 mm external diameter) has been designed to study the behavior of low permeability saturated geo-materials such as stiff clays or argillites under controlled temperature and pore pressure conditions. The main advantage of this device is the short drainage path allowed by the hollow cylinder geometry that is reduced to half the thickness of the sample (10 mm)--four times less than that of standard full cylinder samples of 78 mm height. The reduced drainage path allows a significantly faster resaturation procedure of initially unsaturated samples compared to conventional full cylindrical samples. It also permits the achievement of drained conditions (i.e. negligible excess pore pressure during testing) with a higher loading rate. A numerical simulation of the saturation process demonstrates that the resaturation of the hollow cylinder clay sample can be achieved almost 30 times faster than in standard full samples that are drained at one end, and about seven times faster than in samples drained at both ends. Appropriate loading rates to be used in drained tests on stiff clays and argillites are also discussed based on a numerical simulation of the isotropic compression test. The effect of the deformability of the drainage system on the measured parameters during undrained tests is also analyzed. A correction method is proposed, based on the work of Bishop, by considering the deformability of the porous elements and of the drainage system.