Volume 30, Issue 4 (July 2007)
A Large Diameter Triaxial Apparatus to Measure Pore Pressure and Displacements on a
The development of an apparatus to measure pore pressure and displacements on a pre-existing shear zone/plane during triaxial testing is presented. The apparatus includes a newly developed 405-mm diameter triaxial cell, a miniature pore pressure transducer for monitoring shear-induced pore pressures, and a displacement transducer for measuring shear displacements. Tests were performed by mounting the pore pressure transducer onto the face of a pre-existing shear plane in the specimen and installing the displacement transducer inside the triaxial cell to monitor local deformations. The results reveal that pore pressures measured on the shear plane and the base of specimens of Athabasca clay, Highvale mudstone, and Fort McMurray highly weathered limestone are identical at a shear displacement rate equal or less than approximately 18 mm/day. This implies that when the shear displacement rate is less than about 18 mm/day for rocks/soils that have a permeability greater than 10−8∼10−9 cm/s, the pore pressure obtained from in situ instrumentation, which may not be set exactly on the shear plane, can be used as the shear zone pore pressure.