Key Project Features:
- Soil-Bentonite Slurry Wall
- 30 inches wide
- Average depth of (19 feet), maximum depth of 32 feet
- 8,067 feet long, 155,491 vertical square feet.
- Target Average Permeability of 1×10-7 cm/s
- Road Crossings with a target average UCS of 15-20 psi
- 5’ wide x 2’ deep Temporary Cap
- Soil Cement Bentonite Segment of length 430 feet and an average depth of 18.5 feet.
- 100% Self-Performed
Description of Work:
Geo-Solutions installed a Soil-Bentonite (SB) groundwater cutoff wall on the ePort Redevelopment Project site. This cutoff wall was installed excavating with a PC400 equipped with a 30 inch wide bucket and using the slurry trenching method.
The cutoff wall was excavated to a maximum depth of 32 feet and was excavated in two distinct segments, North and South of Cranes Creek that crossed the site. The total length of the combined walls was approximately 8,067 feet and the total vertical square feet of wall installed was 155,491. The specified hydraulic conductivity requirement for the SB backfill, 1×10-7 cm/s, was achieved or exceeded with all samples. SB backfill samples were taken and tested at a minimum frequency of once every 200 LF.
A temporary cap was installed over the SB backfill consisting of 7.5 foot wide roll of Mirafi HP270 geotextile installed 2 inches below the work platform and covered with lightly compacted site soils.
In addition to the barrier wall and temporary cap, Geo-Solutions also installed several road crossings at predetermined locations along the alignment of the cutoff wall. The road crossings were installed using an excavator to mix dry Portland cement approximately 15 feet below the ground surface with the already in place SB backfill. The road crossings were installed primarily to bring the UCS of the SB backfill / cement mixture up to 15-20 psi in order to facilitate future site use over the weak SB barrier wall. After mixing the SB backfill with cement, the temporary cap geotextile was then laid on top of the cement mixed portions and the elevation was brought back to the ground surface using granular material. A portion of the cutoff wall also was installed using Soil Cement Bentonite (SCB) backfill to increase the strength of the wall next to an existing surcharge pile.
- Large concrete structures encountered in various locations along the trench alignment causing the trench to be wider than designed, one slurry loss, and a minor trench collapse (20-30 feet long).
- Difficult excavation conditions in a hard slag layer that existed over much of the site. The slag layer was so hard that Geo-Solutions was directed to forgo excavation attempts over a portion of the original barrier wall alignment.
- In addition to the subsurface obstructions and obstacles, Geo-Solutions also had to deal with surface obstacles including limited working room next to surcharge piles, a live telephone pole, and a water tank that necessitated the cutoff wall alignment be moved.
- The work platform required constant maintenance as it was largely constructed of loosely compacted fill used to fill voids left from former structures.
Although the project took much longer than expected, Geo-Solutions’ crew was able to overcome the many challenges on this project and ultimately left a well-built barrier wall.