Stem Wall Backfilling With Cellular Concrete
The Job
This work was associated with the construction of a new academic building at a school in Lynchburg, Virginia.
The Challenge
Due to a sloped site, there was up to an 8′ difference in elevation between the existing ground and the desired finish floor elevation. Various options for filling the CMU stem walls included soil, aggregates and EPS foam blocks. EPS foam blocks were chosen to reduce loads on the footings, which would have required deep foundations in the case of soil or aggregate backfilling.
Due to the extensive sub-slab plumbing, the design called for EPS blocks cut to fit the curved walls & uneven ground profile, and then backfilled with 18″ of stone dust, to allow for the plumbers to dig and install the plumbing.
The Solution
CJGeo proposed installing 23lb/cuft cellular concrete to speed up the installation, reduce supply chain risks, and reduce the loads applied to the foundations and underlying soil.
CJGeo placed 1914CY of cellular concrete over three days onsite. All material was walkable within 12 hours, and the project saved approximately 3 weeks relative to the original design’s timeframe.
The cellular concrete was brought all the way to the bottom of the 6″ stone layer below the slab, and the plumbers were then able to excavate through the cellular concrete with a mini excavator and hand tools to install the plumbing, and the trenches were backfilled with 57 stone.
The total load using cellular concrete was reduced by approximately 120lbs/sqft relative to the EPS/stone dust backfill design.
Precast Lagging Wall Lateral Load Reduction
The Job
This work as associated with the replacement of Scaife Hall, at Carnegie Mellon University, in Pittsuburgh, Pennsylvania.
The Challenge
The H-pile and precast lagging wall was situated at the top of a steep slope, which had a Class I railroad at the base. Because of site constraints, an HDPE stormwater detention structure was situated within the fill area, along with extensive stormwater pipes and manholes.
In order to optimize the drilled shafts for the H-piles by reducing the lateral loads, the designer sought a lightweight, permeable backfill material that would not apply lateral loads once in place.
The Solution
CJGeo proposed 20lb/cuft permeable cellular concrete to minimize lateral loading on the wall during construction, buoyancy of of the stormwater system components, and ensure a free draining material.
Because the material is permeable (modified ASTM D-2434 2.0cm/sec), it is freely draining and reduces hydrostatic loads on adjacent structures.
620 cubic yards of lightweight backfill were placed over two mobilizations.
250000 Gallon Oil Tank Abandonment
The Job
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.
The Challenge
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.
The Solution
CJGeo proposed 20lb/cuft cellular concrete for the abandonment grouting. This afforded plenty of factors 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.
Retaining Wall Lightweight Backfill
The Job
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.
The Challenge
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.
The Solution
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 free 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.
5520CY Tank Abandonment
The Job
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 of less than 60lbs/cuft to avoid settlement.
The Challenge
The lightweight fill material had to provide sufficient support for approximately 4′ of compacted fill material, and a delivery truck loading dock, and future building.
The Solution
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.
