In reality, soil is not homogenous all through, and therefore, its characteristics are variable. In what follows, we will be considering the case of a stronger soil underlain by a weaker soil. For this case, two possible figures can be drawn depending on the ratio of H/B, where H is the depth below the footing to the weaker layer. As shown in Figures 6 & 7, if H/B is relatively small, the entire failure surface can be considered to occur in the weak layer, whereas if the ratio of H/B is relatively large, then the entire failure surface is expected to occur in the top layer, the stronger layer.
The 3 most common cases accounted for by Meyerhof are:
Top layer is strong sand and bottom layer is saturated soft clay (f2=0)
Top layer is stronger sand and bottom layer is weaker sand (c1=0, c2=0)
Top layer is stronger saturated clay (f1=0) and bottom layer is weaker saturated clay (f2=0)
Equations for calculating the ultimate bearing capacity for each case have been also derived and are adequately covered in "Foundation Engineering", B. M. Das, Ch. 3 in the corresponding section on layered soils.