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  • Print publication year: 2013
  • Online publication date: April 2013

3 - Laboratory-derived constitutive relations for shear failure


Method and apparatus used

In order to establish the constitutive law for the shear failure (or fracture) of intact rock in the brittle to semi-brittle (or brittle–plastic transition) regimes under seismogenic crustal conditions, it is necessary to carefully observe the entire shear failure process during which the post-failure (or slip-weakening) behavior is stabilized. A sophisticated high-pressure testing apparatus having a stiff loading frame and electronic servo-controls with a 16-bit resolution digital system was constructed for this purpose in our laboratory at the Earthquake Research Institute, the University of Tokyo (Ohnaka et al., 1997). The post-failure behavior can be stabilized even in the brittle regime by enhancing the stiffness of the loading system and properly choosing servo-control variables.

The entire system includes the load frame assembly with which servo-hydraulic actuators are integrated, a triaxial pressure cell, servo-hydraulic intensifiers (for confining pressure and pore pressure), a hydraulic power supply system, a heater and cascade temperature controller, a water cooling system, and a computer-automated system controller with software designed for use with multiple channel servo-hydraulic valves and a heater (for details, see Ohnaka et al., 1997).

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