Ground Subsidence, Collapse, and Heave - Geotechnical Engineering Investigation - page 878

Piping in dispersive clays used in embankment construction is prevented by the proper
design of filters to control internal seepage (see Section 8.4.5) and by the use of materials
that are not susceptible to the phenomenon. Where piping is already occurring it may be
necessary to reconstruct the embankment using proper design and materials, if placing a
filter at the outlet is not effective.

10.6 Heave in Soil and Rock

10.6.1 General

Origins of Ground Heave
Heave on a regional basis occurs from tectonic activity (see Section 11.3.1 and the
Appendix A). On a local basis heave occurs from stress release in rock excavations
(see Section 6.6), expansion from freezing (see Section 7.7.3), and expansion from swelling
in soil or rock (this chapter).

The Swelling Hazard
Swelling in Geologic Materials
Clay soils and certain minerals readily undergo volume change, shrinking when dried (see
Figure 5.11), or swelling when wet. When in the dry state, or when less than fully satu-
rated, some clays have a tremendous affinity for moisture, and in some cases may swell to
increase their volume by 30% or more. Pressures in excess of 8 tsf can be generated by a
swelling material when it is confined. Once the material is permitted to swell, however,
the pressures reduce. There is a time delay in the swelling phenomenon. Noticeable swell
may not occur for over a year after the completion of construction, depending on the soil's
access to moisture, but may continue for 5 years or longer.

Damage to Structures
Ground heave is a serious problem for structures supported on shallow foundations, or
deep foundations if they are not isolated from the swelling soils. Heave results in the uplift
and cracking of floors and walls, and in severe cases, in the rupture of columns. It also has
a detrimental effect on pavements. Shrinkage of soils also causes damage to structures.
Damages to structures in the United States each year from swelling soils alone has been
reported to amount to $700 million (ENR, 1976).

Geographic Distribution
Swelling Soils
Swelling soils are generally associated with dry climates such as those that exist in
Australia, India, Israel, the United States, and many countries of Africa (see Section 7.2.2,
Black Cotton Soils). In the United States, foundation problems are particularly prevalent
in Texas, Colorado, and California, and in many areas of residual soils, as shown on the
map given in Figure 10.39.

Swelling in Rocks
Swelling in rocks is associated primarily with clay shales and marine shales (see Section
6.7.3). In the United States, it is particularly prevalent in California, Colorado, Montana,