Environmental Engineering Reference
In-Depth Information
because of the likelihood that a variation in properties will result in large differential set-
tlements. Adequate site drainage should be provided to prevent ponding and all runoff
should be collected and directed away from the structure. Avoid locating septic tanks and
leaching fields near the structure, and construct all utilities and storm drains carefully to
ensure tightness. Underground water lines near the structures have been double-piped or
encased in concrete to assure protection against exfiltration. In a desert environment,
watering lawns, which is commonly accomplished by flooding, should be avoided, and
areas should be landscaped with natural desert vegetation.
Lime stabilization has been used in Tucson, Arizona, to treat collapsible soils that have
caused detrimental settlements in a housing development (Sultan, 1969). A water-lime
mixture was pumped under high pressure into 2-in.-diameter holes to depths of about 5 ft,
and significant movements were arrested.
Hydrocompaction to preconsolidate the collapsible soils was the solution used by the
California Department of Water Resources for the construction of the California aqueduct
(Curtin, 1973). Dikes and unlined ditches were constructed and flooded along the canal
route to precompact the soils at locations where collapse potential was considered high.
A section of the canal being constructed over areas both precompacted and not precom-
pacted is shown in Figure 10.34; the subsidence effects on the canal sides are evident on
the photo. When hydrocompaction is used, however, the possibility of long-term settle-
ments from the consolidation of clay soils under increased overburden pressures should
be considered.
Vibroflotation was experimented with before the construction of the California aqueduct,
but adequate compaction was not obtained in the fine-grained soils along the alignment.
FIGURE 10.34
Mendoza test plot showing prototype canal section along the California aqueduct. Crest width is 168ft and
length is 1400ft. Note that both the lined and unlined sections of the canal are subsiding where the land was
not precompacted. Concentric subsidence cracks indicate former locations of large test ponds. (From Curtin,
G., Geology, Seismicity and Environmental Impact, Special Publication Association Engineering, Geology, University
Publishers, Los Angles, 1973. With permission. Photo courtesy of California Department of Water Resources.)
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