Skempton 1951 suggested a bearing capacity theory for saturated clay for which É¸ = 0. Skempton gives Nc, the bearing capacity factor on the basis of theory, laboratory tests and field observations. It was found that the value of Nc increased with the increase in Df/B ratio. The expression for Nc proposed by Skempton is given below.
For Strip footings,
Nc = 5(1+0.2Df/B), with a maximum limiting value of 7.5 ———- (1)
For square and circular footings,
Nc = 6(1+0.2Df/B), with a maximum limiting value of 9.0 ———- (2)
For rectangular footings,
Nc = 5(1+0.2Df/B) (1+0.2B/L) for Df/B â‰¤ 2.5 ———- (3)
7.5(1+0.2Df/B) (1+0.2B/L) for Df/B > 2.5 ———- (4)
For É¸ = 0 condition, the net ultimate bearing capacity is given by:
Qnet = cuNÃ§ ———- (5)
Alternatively, the graph given in Fig.1 above can be used to find the bearing capacity factor Nc. Where, Nc (rect) = Nc(sq)[0.84 + 0.16B/L] . As per Skemption, if the shear strength of the soil does not vary more than ± 50 % of the average value for a depth 2/3B below the footing, the average value of cu can be used in the above equation.