Civil Engineering Reference
In-Depth Information
TABLE 14.7
Foundations
Topic
Discussion
General
regulations
General regulations for foundations in the
International Building Code
(2012) are
as follows:
●
Design for capacity and settlement
(Sec. 1808.2). This code section states:
“Foundations shall be so designed that the allowable bearing capacity of the
soil is not exceeded, and that differential settlement is minimized.”
●
Design loads
(Sec. 1808.3). This code section requires that foundations be
designed for the most unfavorable effects due to the combinations of loads.
●
Vibratory loads
(Sec. 1808.4). This code section states: “Where machinery
operations or other vibrations are transmitted through the foundation, con-
sideration shall be given in the foundation design to prevent detrimental
disturbances of the soil.”
●
Shifting or moving soils
(Sec. 1808.5). This code section states: “Where it is
known that the shallow subsoils are of a shifting or moving character, founda-
tions shall be carried to a sufficient depth to ensure stability.”
Shallow
foundations
The
International Building Code
(2012) requires that shallow foundations be
built on undisturbed soil, compacted fill, or CLSM material (Sec. 1809.2). During
construction, it is common for loose soil or debris to be knocked into the foot-
ing excavations during the construction process or during the installation of the
steel reinforcement. It is important that prior to placing concrete, the footings be
cleaned of loose debris so that the foundation will bear on undisturbed soil or
compacted fill.
In terms of the top and bottom surfaces of shallow foundations, the
International
Building Code
(2012) states (Sec. 1809.3): “The top surface of footings shall
be level. The bottom surface of footings shall be permitted to have a slope not
exceeding one unit vertical in 10 units horizontal (10-percent slope). Footings
shall be stepped where it is necessary to change the elevation of the top surface of
the footing or where the surface of the ground slopes more than one unit vertical
in 10 units horizontal (10-percent slope).”
The
International Building Code
(2012) also states that the minimum depth of
shallow footings below the undisturbed ground surface shall be 12 in. (305 mm),
the minimum width of footings shall be 12 in. (305 mm), and that the foundations
be protected from frost (Sections 1809.4 and 1809.5). Regulations for footings on
granular soils are as follows:
“1809.6 Location of footings. Footings on granular soil shall be so located
that the line drawn between the lower edges of adjoining footings shall not
have a slope steeper than 30 degrees (0.52 rad) with the horizontal, unless that
material supporting the higher footing is braced or retained or otherwise laterally
supported in an approved manner or a greater slope has been properly established
by engineering analysis.”
