关键词: 高压实验, 应力降, 粘滑, 刚度

Abstract: Two series of triaxial tests were conducted for investigation of the mechanics of stick slip that occurred at high pressure and low temperature conditions.By the negative stiffness testing which cancels out a portion of compliance of the machine-specimen system,shear stress versus slip curves of granite saw cuts and quartzite shear fractures were obtained under 300MPa confining pressure.The duration of the slip was increased to about 0.5 second which would be otherwise several milli second when loaded by conventional test methodThe process was well recorded by an X-Y recorder whose cut off frequency is 2. 5 Hz.By another test which can reduce the intrinsic machine stiffness to a dislred value,stress drop was found to depend on the value of stiffness while slip distance remains comparable under different stiffness settings.This result is completely different from estimates by conventional friction models,say,the rate and state dependent friction model and slip weakening model.However,the result is similar to that when strength is controlled by geometric constraints of the contacting surfaces as noted by Lockner and Byerlee (1990).

Key words: Stick slip at high pressure, Negative stiffness, Stress drop