Figure 7.6 presents a plot of maximum settlement (i.e., total settlement, r
max) versus maximum
differential settlement Δfrom case studies. Bjerrum (1963) considered only those structures having
comparably loaded footings on sands of uniform thickness. For the case studies used to develop
Fig. 7.6, the maximum differential settlement Δis that which occurred between comparable footings
designed for the same total settlement. As shown in Fig. 7.6, when the total settlement was less than
about 20 mm (0.8 in.), there was considerable scatter in data with no discernable correlation between
total settlement and maximum differential settlement. However, for those structures where the
recorded settlement exceeded about 20 mm (0.8 in.), the differential settlement typically was close
in value to the total settlement. The large values of maximum differential settlement are attributed to
the nonuniformities in natural sand deposits. The differential settlement is often difficult to deter-mine because it depends on the rigidity of the foundation and the nonuniformities in sand deposits,
and hence the maximum differential settlement is often assumed to be 50 to 75 percent of the total
settlement (i.e., Δ=0.5 to 0.75 of r
max
) for cohesionless soil.