HR: 0800h
AN: T41F-1303    [Abstracts]
TI: A New Methodology to Probe the Failure and Compactive Yield Behavior of Porous Rocks Under Undrained Conditions
AU: * Tembe, S
EM: stembe@ic.sunysb.edu
AF: SUNY at Stony Brook, Department of Geosciences , Stony Brook, NY 11794-2100 United States
AU: Vajdova, V
EM: vvajdova@ic.sunysb.edu
AF: SUNY at Stony Brook, Department of Geosciences , Stony Brook, NY 11794-2100 United States
AU: Baud, P
EM: pbaud@eost.u-strasbg.fr
AF: Institut de Physique du Globe (CNRS/ULP), 5 rue Rene Descartes, Strasbourg Cedex, 67084 France
AU: Zhu, W
EM: wzhu@whoi.edu
AF: WHOI, Department of Geology and Geophysics Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Wong, T
EM: teng-fong.wong@sunysb.edu
AF: SUNY at Stony Brook, Department of Geosciences and Department of Mechanical Engineering , Stony Brook, NY 11794-2100 United States
AB: The poromechanical behavior of rocks under undrained condition is of fundamental importance in many geologic and geotechnical problems. In a conventional undrained experiment the saturated sample is deformed under constant confining pressure while fluid movement in or out of the pore volume is inhibited. Maintaining a constant pore volume requires a pore pressure system that contributes negligible volume and compressibility to the overall mechanical response, which is difficult to achieve in a relatively compact rock. To circumvent this difficulty associated with the conventional experiment, we have developed a modified undrained methodology in which the rock sample is deformed while the pore pressure is maintained constant and the confining pressure continually adjusted to maintain the pore volume constant. Triaxial compression experiments were conducted on water saturated samples of Adamswiller and Diemelstadt sandstone at a constant pore pressure of 10 MPa, confining pressure ranging from of 50-275 MPa, and a nominal axial strain rate of 1.9 x 10-5 s$^{-1}$. In a typical test several stress contours for one rock sample at constant porosities ranging from 12-20% can be mapped out. If the elastic volumetric strain is negligible, then such a stress contour corresponds to a plastic yield envelope associated with zero plastic volumetric strain. Mechanical data for drained tests provide constraints on the compactive yield caps at different values of plastic volumetric strain, which are in accord with stress contours derived from modified undrained tests at differential stresses below a critical threshold. Acoustic emission (AE) measurements show that this stress threshold is marked by an upsurge in AE activity that signals appreciable damage and plastic yield.
DE: 5104 Fracture and flow
DE: 5114 Permeability and porosity
DE: 5120 Plasticity, diffusion, and creep
DE: 5199 General or miscellaneous
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting