EXPERIMENTAL STUDY OF STATIC AND DYNAMIC FRICTION BETWEEN SOIL AND TYPICAL CONSTRUCTION MATERIALS

Abstract
A report is made of research carried out to determine, on the basis of laboratory measurements, the coefficient of friction between two sands of different gradation (one with angular and the other with rounded particles) in contact with Portland cement mortar, steel, teflon, and graphite. In the static tests, loads were applied at a uniform rate until slip occurred in approximately 5 minutes. Dynamic loads were applied by means of a shock tube, which produced a step-like forcing function; slip usually occurred in approximately 2 milliseconds or less. It was found that the coefficients of friction depend on the relative size, shape and surface roughness of the sand grains with respect to that of the surface in question; when the sliding surface is 'rough' in comparison with the sand particles, the coefficient of friction approaches the coefficient of internal friction of the sand. Both graphite and teflon serve as friction reducers, compared to the plain surfaces, irrespective of the rate at which slip is initiated. For plain steel or cement mortar, the dynamic coefficient of friction was greater than the static coefficient of friction by about 25 percent, unless the static coefficient was such that sand/sand slip was approached. The angle of shearing resistance of the sand thus provides an upper limit to the coefficient of wall friction at all rates of loading.

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