As part of decommissioning an underground oil tank at an institutional facility in Washington, DC, it needed to be filled with excavatable material that was lighter than the roughly 55lb/cuft heating oil it was designed to hold.
The tank is located in a small empty lot, which is slated for redevelopment in approximately three years.
To be officially considered decommissioned, the tank had to be completely filled. It is slated for removal as part of the redevelopment process of the area (it sits within a future basement excavation) so the fill material had to be excavatable.
CJGeo proposed 20lb/cuft cellular concrete for the abandonment grouting. This afforded plenty of factor of safety to reduce the likelihood of settlement induced by filling the tank, and maximized excavatability
CJGeo placed the fill material over a period of two days onsite. Because cellular grout is highly mobile, no entry was required during the placement of the fill material, which designed a significant amount of risk out of the process.
The 1200CY placement was performed over two days onsite.
Sanitary sewer right of ways straddling lot lines can be particularly troublesome if a problem occurs with a line and trenchless repairs aren’t possible. This was the case on an 8″ gravity line in Arlington, Virginia. Extensive structural damage to the line caused repeated backups and raised stability concerns for multiple retaining walls which had been constructed over the line.
The walls ranged from four to eight feet tall, and were a mix of concrete and natural stone.
Timber-shored, hand-excavated work was done on the high side of the wall to expose and replace the affected lines. Because of stability concerns with the walls, the geotechnical engineer specified material no heavier than 25lbs/cuft.
The only access was pumping material from the street, down a decorative flagstone pathway between two homes, and into the excavated pits.
CJGeo proposed 25lb/cuft wet cast density permeable cellular concrete for the backfill material. Because there is no aggregate, it can easily be pumped through small diameter lines at low pressure, which addressed the accessibility concerns.
Because the material is permeable (modified ASTM D-2434 2.0cm/sec), it is freely draining and reduces hydrostatic loads on adjacent structures.
CJGeo mobilized twice for the phased project, and backfilled each of the pits in a single lift.
As part of a water treatment plant rehabilitation project in Stamford, Connecticut, a 25,000sqft underground tank needed to be abandoned, and the concrete roof removed.
The geotechnical engineer required an average fill density less than 60lbs/cuft to avoid settlement.
The lightweight fill material had to to provide sufficient support for approximately 4′ of compacted fill material, and a delivery truck loading dock and future building.
CJGeo proposed 25lb/cuft permeable cellular concrete with an approximately 10ksf compressive strength to fill the structure.
CJGeo placed the 25lb/cuft cellular concrete in daily pours up to 980CY, in single lifts up to 36 inches thick. The roof demolition debris dropped onto the top of the cellular concrete and was then buried with fill material.
The total project volume was approximately 5520CY.