A note on the choice of interfacial friction angle

Estimates of interfacial friction angle (ô) are necessary for the design of retaining structures and deep foundations. Recommendations in the literature regarding ôvalues are often contradictory and are therefore not easy to apply in geotechnical design. A critical examination of past studies in terms of data generation techniques used and conclusions drawn indicates that two distinctly different test procedures/techniques have been evolved. The interfacial situation in practice can also be categorized into two broad types. These two types of interface problems in geotechnical engineering are (a) the structure is placed on the free surface of prepared fill (type A situation) and (b) the fill is placed against the material surface which functions as a confined boundary (type B situation). The friction angle ô depends on the surface roughness of the construction material. But in the type A situation, it is independent of density and its limiting maximum value (onm) is the critical state friction angle <j>n. In the type B situation, it is dependent on density of the fill and its limiting maximum value is the peak angle of internal friction cip of the fill.