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The limiting contact friction between sand and steel, cement mortar, graphite, and teflon surfaces was measured in the laboratory. The coefficients of (wall) friction were obtained using static and dynamic loadings with particular reference to conditions at the time slip was initiated. The coefficient of friction increases with the surface roughness and angularity of the sand grains, and as the roughness of the contact surface increases with respect to the size of the sand particles. For steel and mortar surfaces dynamic friction was greater than static friction by about 20 percent unless the surface was sufficiently rough that sand/sand slip was approached. The (static) angle of shearing resistance was the upper limit of the coefficient of friction for all static and dynamic tests where slip was initiated from 1–2 ms to 5 min (loading rates from 5 × 105 to 0.5 psi/min). Under static loading conditions teflon and graphite reduced wall friction by one-half to one-third; at high loading rates graphite was a more effective lubricant than teflon.
Assistant professor of Civil Engineering, Georgia Institute of Technology, Atlanta, Georgia
Professor of Soil Mechanics, Purdue University, Lafayette, Indiana
Stock #: JTE10893J