Foundations for buildings and structures founded on
expansive soils shall be designed in accordance with Section 1808.6.1 or
1808.6.2.
1. The soil is removed in
accordance with Section 1808.6.3; or
2. The building official
approves stabilization of the soil in accordance with Section 1808.6.4.
1808.6.1
Foundations.
Foundations placed on or within the active zone of expansive soils shall be
designed to resist differential volume changes and to prevent structural damage
to the supported structure. Deflection and racking of the supported structure
shall be limited to that which will not interfere with the usability and
serviceability of the structure.
Foundations placed below where volume change occurs or below
expansive soil shall comply with the following provisions:
1. Foundations extending into or penetrating
expansive soils shall be designed to prevent uplift of the supported
structure.
2. Foundations
penetrating expansive soils shall be designed to resist forces exerted on the
foundation due to soil volume changes or shall be isolated from the expansive
soil.
1808.6.2
Slab-on-ground foundations. Moments, shears and deflections for use in
designing slab-on-ground, mat or raft foundations on expansive soils shall be
determined in accordance with WRI/CRSI Design of Slab-on-Ground
Foundations or PTI Standard Requirements for Analysis of
Shallow Concrete Foundations on Expansive Soils. Using the moments,
shears and deflections determined above, nonprestressed slabs-on-ground, mat or
raft foundations on expansive soils shall be designed in accordance with
WRI/CRSI Design of Slab-on-Ground Foundations and
post-tensioned slab-on-ground, mat or raft foundations on expansive soils shall
be designed in accordance with PTI Standard Requirements for Design of
Shallow Post-Tensioned Concrete Foundations on Expansive Soils. It
shall be permitted to analyze and design such slabs by other methods that
account for soil-structure interaction, the deformed shape of the soil support,
the plate or stiffened plate action of the slab as well as both center lift and
edge lift conditions. Such alternative methods shall be rational and the basis
for all aspects and parameters of the method shall be available for peer
review.
1808.6.3
Removal of
expansive soil. Where expansive soil is removed in lieu of designing
foundations in accordance with Section 1808.6.1 or 1808.6.2, the soil shall be
removed to a depth sufficient to ensure a constant moisture content in the
remaining soil. Fill material shall not contain expansive soils and shall
comply with Section 1804.5 or 1804.6.
Exception: Expansive soil need not be removed to
the depth of constant moisture, provided the confining pressure in the
expansive soil created by the fill and supported structure exceeds the swell
pressure.
1808.6.4
Stabilization. Where the active zone of expansive soils is stabilized in
lieu of designing foundations in accordance with Section 1808.6.1 or 1808.6.2,
the soil shall be stabilized by chemical, dewatering, presaturation or
equivalent techniques.
