- Q.We are planning to build on
a site with fine sand and silt soil. Code requires a
foundation depth of at least 2 feet, but during the
summer the water table rises to within 2 feet of the
surface because of the irrigation of adjacent fields.
How should the footing be designed to prevent possible
settlement?
A.Washed sand, with
particles that have been rounded, acts differently
than "sharp" sand, when it is wet. It may be
necessary to support the footing on piles to
prevent movement with the extreme changes in soil
moisture content at your site. This is an instance
when the services of a soils engineer are well
worth their cost. Without knowing detailed
information about the soil, including the shape of
the sand particles and the type of subsoil, there
can be no definitive answer.