When a rigid concrete retaining wall is to be used, the designer must consider that
such a wall can tolerate only minimal differential settlement. If differential settlement
is predicted, the designer may have to accommodate this situation by vertical joints in
the wall and other systems of articulation in the wall. In many instances, this type of
wall, under situations where differential or excessive settlement is anticipated, will
require deep foundations such as caissons or piling driven to firm supporting material.
Alternatively, subexcavation and replacement of poor material at the base of the wall
desired, samples will be necessary. The samples can be disturbed or undisturbed. The
disturbed sample is generally taken in cohesionless soils and is used for classification
and for moisture determination and compaction tests. More commonly, such samples
may be taken by driving a heavy walled sampler into a clean hole. The size of the
sampler or spoon varies from 2 in (50 mm) O.D. to 41⁄2 in (112 mm) O.D. When a standard
penetration test (SPT) is required, the sample is obtained by driving a 2-in (50 mm)
O.D. by 13⁄8-in (34 mm) I.D. sampler