An important consideration is that for the strip footing, the shear strength is actually based on a
plane strain condition (i.e., the soil is confined along the long axis of the footing). It has been stated
that the friction angle f is about 10 percent higher in the plane strain condition as compared to the
friction angle f measured in the triaxial apparatus (Meyerhof, 1961; Perloff and Baron, 1976). Ladd
et al. (1977) indicated that the friction angle f in plane strain is larger than f in triaxial shear by 4°
to 9° for dense sands. A difference in friction angle of 4° to 9° has a significant impact on the bearing
capacity factors. In practice, plane strain shear strength tests are not performed and thus there is
an added factor of safety for the strip footing as compared to the analysis for spread or combined
footings.