Point Bearing Piles in Sand Underlain by Clay. The lower left diagram in Fig. 8.17 shows the
condition of a soft clay layer underlain by a sand stratum. The sand stratum provides most of the vertical
resistance and hence the pile group is considered to be end bearing. For this case, the upper sand
layer is assumed to be thick enough that a punching failure is not a concern. As shown in Fig. 8.17,
the 2:1 approximation is assumed to start at the top of the sand layer and is used to calculate the
increase in vertical stress (sz _sv) and hence the primary consolidation settlement and secondary
compression of the soft clay layer having a thickness defined as H.