The Job
This slurry wall gap closure grouting work is part of CJGeo’s continuing permeation and water control work at the RiverRenew project in Alexandria, Virginia. At an outfall structure that will pull wet weather flow from an existing CSO, which is a roughly 8’x8′ box culvert. It is currently suspended from a large beam and webbing. The beam spans a roughly 40′ wide excavation between two parallel slurry walls. The slurry wall gap is approximately 20 feet wide.
The Challenge
Excavation at this location has continued to uncover seams of highly permeable sand and gravel. The material is quickly recharging due to close proximity to the Potomac River. It also recharges with ground water flowing through the bedding stone below the box culvert from the uphill catchment area.
The Solution
Due to ground-level obstructions, drilling from the surface into the grouting zone isn’t possible. CJGeo designed a percussion-driven sacrificial tubing plan to install the grout. No sonic drilling needed.
The grout curtain is approximately two feet thick. It is fourteen feet deep. It is located about two feet behind the desired face of excavation.
All of the work was done from a mud mat installed by the contractor. Evaluated grouts included:
- colloidal silica grout, which would perform well from a permeation perspective, but likely be susceptible to washout. Colloidal silica would also potentially not perform well during lagging installation due to the friable nature of treated soils, and high groundwater head
- acrylic grout, which has performed very well onsite in previous work.
CJGeo mobilized to the site and completed the permeation grouting over a period of a few daytime shifts. This allowed the contractor to resume excavation within the structure.
Speak With An Expert
Facing a similar challenge to this slurry wall gap closure grouting project? Give us a shout or shoot us a text. Click the state marker for the location of your project for contact info for the appropriate rep.
