Stick-Slip of Lightly Loaded Limestone

The phenomenon of stick-slip of a limestone tested in direct shear at a constant rate of strain under normal loads of 0.75 to 20.00 kg/sq cm and the temperatures from 30 to 200C was investigated. Stick-slip was found to depend upon the temperature, normal load, and previous frictional history of the rock. Stick-slip could always be induced from smooth slip by raising the temperature. Temperatures above that required to induce stick-slip result in larger slips, longer sticks, and higher shear load relaxations. At normal loads above 3.00 kg/sq cm, stick-slip began at 30 degrees. Accumulation of debris has the same effect as lightening normal load, allowing smooth slip below 100C. Smooth slip below this temperature is attributed to adsorbed water. The dependence of stick-slip upon temperature and reaction to the creation or introduction of debris lead to the conclusion that stick-slip of limestone is a result of asperity of asperity bonding.
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