The trencher can excavate in a water-filled trench without having to dewater or install sheet piles
to temporarily stabilize the trench walls. Because the boom is positioned almost vertically during
excavation, a trench slope is not created and greatly minimizes the amount of generated trench
spoils. One other advantage is a fast production rate. At the Elizabeth City site, a reactive cell
150 ft long, 2 ft wide, and 26 ft deep was installed in one day (USACE 1997). Also, it is ideal for
sites with constrained working space and minimizes soil disturbance to allow for work in
sensitive areas. Drawbacks include a shallow depth capability and problems with excavating wet,
very unconsolidated materials, which may cause difficulties in bringing trench spoils to the
surface (USACE 1997). Obstructions such as large cobbles and boulders can also disrupt the
digging process. Quoted costs for this technique are between $5/ft
2
and $12/ft
2
for emplacement,
not including mobilization or reactive medium costs.