6.3.1 Soil Weight Parameter. G

The bearing capacity of footings depends not only on the mechanical properties of the soil (cohesion c and friction angle ?), but also on the physical characteristics of the footing (width B, depth D, and roughness ?). For a Coulomb material, Cox (1962) has shown that for a smooth surface footing bearing on a soil subjected to no surcharge, the fundamental dimensionless parameters associated with the stress characteristic equations are ? and G = ? B/2 c, where ? is the internal friction angle, c is the cohesive strength, ? is the unit weight of soil and B is the width of the footing. If G is small the soil behaves essentially as a cohesive weightless medium. If G is large soil weight rather than cohesion is the principal source of bearing strength. For most practical cases one can expect that ? ties in the range 0 -40 and G will range from 0.1 to 1.0. These limits assume that c ranges from 500 psf (24 kN/m ²) to 1000 psf (48 kN/m ²), and that the footing width ranges from 3 to 10 feet (0.9 to 3.05 m). Two additional parameters are needed here, namely ? and D/ B where ? is the friction angle between the footing base and the soil, and D is the...