Hydraulic Isolation of Lagoons or Holding Ponds
Thornton, CO: East Sprat Platte Reservoir, Soil-Bentonite Slurry Wall
Geo-Con installed a slurry wall around a former sand and gravel pit along the South Platte River. The slurry wall was part of a larger reservoir project to create additional municipal water storage for the City of Thornton Colorado.
The total slurry wall installed is approximately 315,000 square feet, with depths varying from 32 to 49 feet. The total length of wall is approximately 8,700 feet. The wall is keyed 6 to 17 feet into the underlying Blue Shale layer. Key depth was determined by the Engineer based on the presence of weather shale and sandstone. Geo-Con created backfill with trench spoils along with dry bentonite to achieve permeability in the range of 1x10-8 cm/sec. This low permeability will help to meet the State of Colorado Engineer's Office requirements for leakage in this type of water storage system.
The key challenge on the project was completing approximately 1,500 feet of the slurry wall using remote mixing. This was done by loading trench spoils directly into off-road dump trucks, mixing in a fixed location, and trucking the soil-bentonite backfill to the trench. The remote mixing was necessary due to narrow (15 to 20 ft wide) work platform areas.
Other challenges included coordination with the other contractors on the site, particularly the installation of a groundwater drain parallel with the slurry wall, and excavating through the hard sandstone layers in isolated areas to reach the competent shale.