Environmental Engineering Reference
In-Depth Information
FIGURE 3.11
Vertical soil mixing. (Reproduced with permission from Geo-Con, Geo-Solutions Inc.)
PRB. This technique is best used in soft soil. Deep-soil mixing can be used
at depths up to 40 m, creates minimal spoils, and has a higher production
rate with lower costs than jet grouting (Geo-Solutions Inc). Because the soil
is mixed with the slurry instead of being replaced, the slurry must be more
concentrated than is the case for jet grouting. Soil mixing generally achieves
greater PRB uniformity compared to the injection and fracturing techniques.
The mixing results in a higher hydraulic conductivity of the columns rela-
tive to the surrounding soil and consequently a slight increase in the capture
zone of the wall. Mixing is also provided upstream of the barrier to maintain
parallel flow lines entering the PRB.
3.4 Conclusion
Among the existing remediation options, PRB is a very promising tech-
nology in terms of operation and maintenance costs, as well as stability of
performance. PRB installation is expensive but once installed it remains in
place for decades. However, the scope for troubleshooting after installation
is limited, so design selection and installation of the system are the keys for
ensuring consistent performance. The type of design determines the way
in which the plume is captured. The choice of the design and construction
techniques is essential for the success of a PRB which is site-specific. To date,
there are only about 20 years of operating data available on PRBs, although a
contaminated plume may last for many decades. More research is therefore
needed on the evaluations of performance and longevity of reactive barriers.
Contingency plans needs to be incorporated in all PRB designs in the event
of the barrier failing to perform. Existing data show that it may take many
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