Frictional characteristics of typical rocks

Abstract

Detailed laboratory experiments have been performed on the frictional characteristics of various rocks. Frictional behavior greatly depends not only upon rock type, but upon such surface condition as roughness. The behavior of soft rock is more influenced by roughness than that of hard rock. Frictional behavior is classified into the four types: (1) the behavior characterized by both the predominant force drop at initial sliding and stable sliding subsequent to the predominant force drop, (2) the behavior characterized by both the predominant force drop at initial sliding and a series of sticks and slips, (3) frictional sliding occurring stably without any sudden slip, and (4) the behavior characterized only by a series of sticks and slips. The intermediate behavior between type 3 and type 4 is also observed: stable sliding precedes stick-slip. Frictional force increases with displacement (displacement hardening). This is attributed to the development of adhesive or abrasive wear (gouge) particles on sliding surfaces with increasing displacement at an applied constant normal force, The scatter of the measured values of friction on nominally identical specimens under nominally identical conditions is related to the difference in the amount of wear particles developed on sliding surfaces between runs. The experimental relation between friction and the amount of gouge particles is analyzed from a theoretical viewpoint. It is found that stick-slip occurs only when the amount of wear particles is small, and that frictional sliding takes place stably when the gouge is developed abundantly over the whole of the sliding surfaces. The controlling mechanism of friction for uniform soft rocks, such as limestone and marble, is distinctly different from that for such rocks as granite and monzonite which contain various minerals of different hardness. The effects of normal stress and loading rate on friction are also investigated. © 1975, The Seismological Society of Japan, The Volcanological Society of Japan, The Geodetic Society of Japan. All rights reserved.