Choosing the Best Design and Construction Technologies for Permeable Reactive Barriers - Permeable Reactive Barrier: Sustainable Groundwater Remediation - page 58

construction of deeper barriers; however, particular care needs to be taken
in designing such gel mixtures.
Caldwell Trucking, northern New Jersey (USA), have used a gel to suspend
and transport iron filings into the subsurface. They found that the gel must
be of sufficiently high quality and purity to have no impact on the iron reac-
tivity and permeability. The injections of a rapid breaking enzyme is capable
of breaking iron/gel mixtures even at the highest pH. The poor performance
of this PRB is believed to be due to changes in the GW flow regime resulting
from the injection of granular iron into the fractured bedrock, and the slow
breakdown of guar gum gel.
3.3.2.2 Jetting
High-pressure jetting is an established practice to inject grouting agents to
improve the structural characteristics of soil for construction purposes, as
shown in Figure 3.10. Recently, injection of grout has been used to construct
funnel walls and in order to get the required length and thickness of the
funnel (Geo-Solutions Inc). Jetting is a sound technique for installing a wall
around obstructions such as boulders or a utility line. Furthermore, it has
the advantage of the small equipment requirements and a lower mobiliza-
tion cost.
3.3.2.3 Soil Mixing
In deep-soil mixing, a hollow-stem auger with special mixing paddles is
lowered to the desired depth and rotated to mix the soil (see Figure 3.11).
As the auger is removed, reactive slurry is injected through the drill stem.
A succession of these penetrations will create a row of columns to form a
FIGURE 3.10
Jet grout drill with jets activated. (Reproduced with permission from Soilmec ® Drilling and
foundation equipments.)