Traditional methods for "sand-tightening" rubble structures
include dismantling the structure to rebuild core sections,
chinking stone in voids along surfaces, adding additional stone
layers, etc. A cost effective alternative to traditional
practices has been determined to be drilling and grouting
(sealing) of the structure (Simpson 1989).
FIELD EXPERIENCES:
Several existing permeable coastal structures have been sealed by
cement-sand mixtures, chemical grouts, and asphaltic compounds,
s t o n e , and steel sheet-pile. These cases are discussed below
with the intention of sharing on-the-job experiences (lessons
learned) in an area where little guidance exists outside a few
specific Corps Districts. Additional information on void-sealing
may be obtained from Simpson, et al 1990.
Mission Bav, California, Jetty Sealinq:
Located adjacent to the San Diego River mouth on the coast of
southern California, Mission Bay entrance is protected by
jetties. A common jetty (middle jetty) separates river discharge
The
from small-boat navigation and tidal flows of the bay.
project also has another structure that forms the north jetty of
the bay channel, as well as a third jetty comprising the south
jetty of the river channel. Shoaling of the Mission Bay channel
was attributed to sand passing through both the north and middle
jetties.
In 1955, a total of 3,000 tons of sealing stone was placed on the
seaward slope of the north jetty within the limits of the
littoral zone. It was anticipated that waves would drive the
The seal stone
stones into the interstices of the structure.
ranged from 1 l/2-in to 6-in diameter. This measure retarded the
movement of sand, but sediment continued to move through the
It was decided that the jetties must be sealed in a
jetty.
manner that would produce a permanent and complete impermeable
barrier.
A cement-sand material with admixtures was used to seal the
jetties in 1959. The material was pressure injected through
holes. drilled through the jetty crests. The sealant mix included
s a n d , cement, clay, calcium chloride, and water. It was injected
through a 1 l/2-in diameter hose, and sealant holes were drilled
roughly 6.5 ft apart.
After rehabilitation, sand accumulations on the channel sides of
the jetties disappeared, indicating the sealing was successful
(Loudon 1959). Since that time, however, the structures have
been battered by a series of intense winter storms causing
extensive armor stone displacement, and probably internal core
and sealant damage. Additional armor stones have been placed on
the cover layer with no repairs to the barrier curtain created by
the sealing process. Recent observations reveal that most of
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