The foundation of a building transfers the dead and
live loads of the superstructure to the soil that has
enough bearing capacity to support the structure in a
permanent, stable position. Footings are used under
foundation components, such as columns and piers, to
spread concentrated loads over enough soil area to
bring unit pressure within allowable limits.
Foundation design is determined not only by the
weight of the superstructure but also by occupancy or
use of the building or structure and by the load-bearing
capacity of the soil at the site. The latter conditions
may change and introduce maintenance and repair
problems even in initially well-designed foundations.
Foundations should be inspected at least annually
and more often where climate, soil conditions, or
changes in building occupancy or structural use
present special problems. Evidence of initial
foundation failure may be found during routine
inspection of other structural components.
A foundation should be checked regularly for
proper elevation and alignment. Complete failure in a
foundation is rare; however, some settling or
horizontal displacement may occur.
Some common causes of foundation movement
include the following:
The structure is overloaded.
Excessive groundwater that reduces the bearing
capacity of the soil.
Inadequate soil cover that fails to protect against
Adjacent excavations that allow unprotected
bearing soil to shift from under foundations to the
Some indications of localized foundation
Damaged framing connections
Leakage through a displaced roof
Corrective actions that can be taken to alleviate
foundation displacement include the following:
Replace any missing or dislodged part of the
Repair cracks or open joints in concrete or
masonry foundation walls.
Replace defective wood members.
Replace unstable fill around the foundation with
clean properly compacted fill.
Remove growing roots of trees or shrubs that
may dislodge footings or foundations.
Increase bearing area of inadequate footings.
Maintain enough soil cover to keep footings
below the freezing zone.
Prohibit loads from exceeding the design loads
of buildings and structures.
Isolate foundations from heavy machine
operations by providing independent footings and
foundations for heavy machines.
Air-conditioning equipment, cooling towers, and
compressors should be provided with cork or rubber
isolation mounts to prevent transmission of vibrations
to the structural frame of the building.
When excavations are made near the footings of
buildings, care must be taken in removing bearing soil
under existing structures. Temporary stabilization can
be gained by shoring, underpinning, or needling to
relieve pressure of the footings on the soil. Sheetpiling
may be driven and supported laterally to contain the
bearing stress in the soil under the footings.
When water erosion removes soil from around and
under footings some means of erosion prevention,
such as ditching or the use of splash blocks, must be
Footings that fail because of insufficient bearing
area must have their bearing area increased. The
amount of movement in the wall dictates the repairs
necessary. Minor settlement, especially when
uniform, may require no repair. If serious settlement
occurs, the wall may have to be jacked back to its
original elevation, a new footing provided, and repairs
made to the wall.
Improved drainage is the basic solution to the most
common groundwater problems (fig. 7-1). Moisture in
structures caused by a high water table can be drained
away from a foundation by the installation of
open-joint drain tiles surrounded by loose gravel fill.
The drains should be laid so as to drain the water away
from the footings and into a sump with a