When it is important to minimize movement of the
foundation before lifting.
When the soils are too hard to drive steel or concrete
For some structures, it is not possible to generate enough pressure
to drive a steel or concrete piling. This is particularly true for
small structures. In such cases, the process of driving a piling
can literally lift the majority of a small structure off of the
ground without generating enough pressure to drive a piling. At
other times, a home may have loose and unstable brick veneer, or
other problems that make minimizing pre-lift movement important.
When drilled piers are installed, it is necessary to drill a shaft
deep into the ground. All of the dirt that is drilled out of the
ground must be hauled off. After the shafts are drilled, steel reinforcing
must be lowered into the shafts. Next concrete must be carried in
and poured into the shafts. Finally, the concrete must cure for
a week before it can be used to lift a foundation. What all this
means is that drilled shafts are much messier and much slower to
install than pilings. As a result, drilled piers are generally only
used when there is a specific need.