ABSTRACT
The undrained condition is defined theoretically as a condition in which there is no change in the fluid mass of the porous material. For performing an undrained test in the laboratory, this condition cannot be achieved just by closing the valves of the drainage system as it is done classically in a conventional triaxial system (Figure (1)). In a triaxial cell, the tested sample is connected to the drainage system of the cell and also to the pore pressure transducer. As the drainage system has a non-zero volume filled with water, it experiences volume changes due to its compressibility and its thermal expansion. The variations of the volume of the drainage system and of the fluid filling the drainage system induce a fluid flow into or out of the sample to achieve pressure equilibrium between the sample and the drainage system. This fluid mass exchanged between the sample and the drainage system modifies the measured pore pressure and consequently the measured strains during the test. Wissa (1969) and Bishop (1976) were the first who studied this problem for a mechanical undrained loading and presented a method for correction of the measured pore pressure. Ghabezloo and Sulem (2009, 2010) presented an extension to the work of Bishop (1976) to correct the pore pressure and the volumetric strain measured during undrained heating and cooling tests, as well as undrained compression tests, by taking into account the compressibility and the thermal expansion of the drainage system, the inhomogeneous temperature distribution in the drainage system and also the compressibility and the thermal expansion of the fluid filling the drainage system. The correction method depends also on the porosity, the compressibility and the thermal expansion of the tested porous material.
