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

摘要： 通过负刚度实验,得到了300MPa围压条件下花岗岩锯切面和石英岩剪切破裂面的剪应力-滑动曲线。突发滑动的持续时间从一般位移控制条件下的几毫秒延长到0.5s左右。并在普通函数记录仪上对滑动过程曲线作了全过程的记录。又将压机刚度降为任意设定值,可得到应力降与刚度相关而滑动距离基本不变的结果。这一结果与速度依赖性摩擦本构律及滑动弱化本构律所估计的结果不同,它类似于滑动面几何约束控制的滑动依赖性本构关系。

关键词: 高压实验, 应力降, 粘滑, 刚度