Grout Curtains
Description
Grout curtains are thin, vertical, grout walls installed in the ground. They
are constructed by pressure-injecting grout directly into the soil at closely
spaced intervals. The spacing is selected so that each ÒpillarÓ of grout intersects
the next, thus forming a continuous wall or curtain. Typical grouting materials
include hydraulic cements, clays, bentonite, and silicates. However, these
materials may crack or may not be durable or chemically compatible. Polymer
grouts are used for barrier applications because they are impermeable
to gases and liquids and resist radiation, as well as acidic and alkaline
environments. Grout curtains are similar to slurry walls
although they do not require as extensive trenching. Grout is injected with
grouting jets, which use a high-pressure fluid stream (i.e., slurry or water)
to erode a cavity in the soil.
Limitations and Concerns
An underground injection permit may be required.
Keeping nozzles clear, maintaining air flow, and effectively creating a wall
without defects have been problematic in certain environments and operating
conditions. For instance, if very coarse-grained materials are encountered,
defects in the curtain may occur. Therefore, the site must be well
characterized to minimize unexpected geologic conditions. Additionally, if the
jets are turned on and off, they may become clogged.
The orientation of the jets must be precise to ensure the curtain is
continuous. At one demonstration, magnetic anomalies created problems with the
orientation of the directional tool.
Applicability
Grout curtains may be used up-gradient of the contaminated area, to prevent
clean water from migrating through waste, or down-gradient, to limit migration
of contaminants.
Grout curtains are generally used at shallow depths (30 to 40 ft maximum
depth). High-pressure jetting appears to be a cost effective means to place
physical barriers in unstable soils, near foundations, and around underground
obstructions.
Technology Development Status
Grout curtains have been widely used; they are a commercial technology.
However, some of the jet grouting systems are still in the pilot stage.
Web Links
http://www.pdhcenter.com/courses/c192/c192.htm
(course outline on subsurface barriers).
http://www.sandia.gov/Subsurface/factshts/ert/ssb.pdf
Other Resources and Demonstrations
See http://www.clu-in.org/download/contaminantfocus/dnapl/Treatment_Technologies/Containment-1995.pdf
for description of surface barriers, properties, and construction. (Chapter 2)