Lightweight Stem Wall Backfill
The Job
This lightweight stem wall backfill work is part of the construction of a new academic building at a school in Lynchburg, Virginia.
The Challenge
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. Otherwise, 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
The goal was to speed construction and reduce costs. CJGeo worked with the general contractor, structural engineer and geotechnical engineer to design a self-consolidating backfill system as a geofoam alternative. The final design for the lightweight stem wall backfill was 25lb/cuft CJFill-Ultra Lightweight load reducing backfill.
Using the dry batch generation process, a single CJGeo crew made up to two hundred cubic yards per hour of CJFill-UL. Pouring in two foot lifts, the work took about four days onsite. Instead of having to install an 18″ thick sand layer, the plumbers hand dug through the CJFill-UL to install the plumbing. Plumbing trenches were backfilled with stone dust.
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Precast Lagging Wall Lateral Load Reduction
The Job
This load reduction backfill work as associated with the replacement of Scaife Hall, at Carnegie Mellon University, in Pittsburgh, Pennsylvania.
The Challenge
The H-pile and precast lagging wall is at the top of a steep slope. There is a Class I railroad line at the base. Because of site constraints, an HDPE stormwater detention structure is 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 CJFill-High Permeability cellular concrete. CJFill-HP would 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 to complete this load reduction backfill project.
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250000 Gallon Oil Tank Abandonment
The Job
This oil tank abandonment project is located in the nation’s capitol, Washington, DC. As part of decommissioning an underground oil tank at Howard University 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 under a small empty lot. The lot is up for redevelopment in approximately three years.
The Challenge
For a complete decomissioning, the tank had to be completely full of grout. Since it sits within a planned basement excavation, the fill material has to be easily excavatable.
The Solution
CJGeo proposed 20lb/cuft cellular concrete for the oil tank abandonment grouting. This afforded plenty of factors of safety to reduce the likelihood of settlement induced by filling the tank and maximized excavatability. The removability modulus of 20lb/cuft (a quantifiable method for determining excavatability of various types of flowable fill) is much less than one. This means it is easily hand excavatable.
CJGeo placed the CJFill-Ultra Lightweight 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.
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Retaining Wall Lightweight Backfill
The Job
This retaining wall lightweight backfill project is located in Arlington, Virginia. Arlington is a hilly, relatively dense suburb of Washington, DC. 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 for the backfill after open cut repairs were complete.
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 lightweight CJFill-High Permeability for the backfill material. CJFill-HP contains no aggregate. Therefore, it’s can easily pumpable through small-diameter lines at low pressure, which addressed the accessibility concerns.
25lb/cuft CJFill-High Permeability is permeable (ASTM D-2434 2.0cm/sec). Therefore, 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.
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Sedimentation Tank Abandonment
The Job
This sedimentation tank abandonment project is located in Stamford, Connecticut. As part of a water treatment plant rehabilitation project 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
- a future building.
To reduce the risk of inducing settlement, the tank fill material had to provide 500PSF of capacity for future loading.
The Solution
CJGeo proposed 25lb/cuft permeable cellular concrete with an approximately 10ksf compressive strength to fill the structure.
CJGeo placed the 25lb/cuft CJFill-High Permeability (CJFill-HP) cellular concrete in daily pours up to 980CY. Lift heights were up to 36 inches thick.
The total project volume was approximately 5520CY. After the CJFill-High Permeability cellular concrete was in place, the roof was demo’d. The roof debris rests directly on top of the cellular concrete. The site was then brought up to grade with common borrow.
Any precipitation that permeates through the common borrow runs through the layer of CJFill-HP. Then, it flows along the sloped bottom of the tank to a daylight drain at the low end.
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Facing a similar challenge to this sedimentation tank abandonment 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.
