INTERFACIAL FRICTION BETWEEN SANDS AND SOLID SURFACES.

Abstract

It has been established that the friction angle delta between sand and solid surfaces is influenced by the mode of shear resulting from differences in preparation of the interface, The solid material can be placed over the prepared sand bed (type A mode of shear). Alternatively, the sand bed can be prepared over the solid material (type B mode of shear), The apparatus types available in the literature to evaluate delta can be grouped into two categories based on which mode of shear they simulate-type A apparatus (solid material over sand) and type B apparatus (sand over solid material). The results of a series of interface shear tests between sands of different particle size and solid inextensible surfaces of different roughness using modified direct shear apparatus resembling type A and type B shear modes are reported in this paper. A normalized interface roughness parameter 'relative roughness R' has been defined. A correlation between the ratio of peak friction angle (delta(pB)) obtained from type B apparatus and the peak angle of internal friction (phi(p)) and R has been proposed for the rapid evaluation of friction angle. For all practical purposes the critical state friction angle (delta(cvB)), obtained from type B apparatus, and friction angle obtained from type A apparatus (delta(cvA)) can be taken as the same. Hence type B apparatus has the advantage of yielding delta values applicable to both type A and type B situations.