T Wall Lightweight Backfill
The Job
This T wall lightweight backfill project is located in Boston, Massachusetts. The bridge is located on the Lowell Line, within the MBTA‘s Commuter Rail Maintenance Facility.
The Challenge
CJGeo has been involved in this alternative delivery project since 2020, helping to optimize the use of CJFill-Ultra Lightweight fill to facilitate constructing a new embankment over underlying compressible soils.
In this specific location on the project, curved T walls were installed along the curved alignment (different radius) of the existing embankment. A sheet pile SOE retains the existing embankment. Due to highly irregular spaces, limited access, lightweight aggregate, such as foamed glass, would be exceptionally difficult to install and ensure adequate compaction.
The Solution
CJGeo proposed 26lb/cuft CJFill-Ultra Lightweight as the optimal material for the T wall lightweight backfill. The lowest 4′ is CJFill-High Permeability. Because CJFill is a self consolidating fill, there’s no compaction required. This practically eliminates chances of backfill consolidation. On a curved, relatively high speed commuter rail alignment, settlement could be quite risky if it were to occur.
For the first phase, CJGeo mobilized a single dry batch cellular grout plant. The work took a total of five days.
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Hobas Pipe Backfilling
The Job
This Hobas pipe backfilling project is located in Baltimore, Maryland. It is one of the last steps in an emergency storm drain collapse project.
The Challenge
The original design for this project was to slip line a roughly 100 linear foot length of 108″ brick sewer that had collapsed. There was a massive void above the pipe, which was going to be filled with CJFill-Ultra Lightweight after the new pipe was slid in. However, the soil collapsed and the repair turned into an open cut repair.
The pipe is more than 100 years old, and was installed in a rock trench, the walls of which were uneven and unstable. Extensive rock bolting and stabilization was installed to facilitate the installation of the pipe. In order to ensure uniform bedding and stability of the new pipe, Hobas and the EOR recommended backfilling the pipe to at least 1′ above the crown with self-consolidating fill.
150lb/cuft flowable fill would have resulted in tremendous uplift forces on the pipe, unless installed in impracticably thin layers.
The Solution
CJGeo proposed cellular grout as an alternative, in order to reduce the uplift while decreasing the number of lifts.
Due to water infiltration near the invert, the first lift was done using 65lb/cuft CJFill-Under Water. Once the first lift was in place, the placement was switched to CJFill-Standard.
All material was generated onsite from bulk cement using CJGeo’s colloidal dry batch generation process.
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Underground Storage Tank Fill
The Job
This underground storage tank fill project by CJGeo is located at a food manufacturing facility near Harrisonburg, Virginia. The tank is 30 thousand gallons, and designed to store diesel to feed backup power generation for the facility. As part of an equipment upgrade, the tank is no longer in use, and had to be filled.
The Challenge
The best way to address unused underground storage tanks that aren’t removable is to fill them. If left empty and out of mind, abandoned empty tanks can cause serious problems, such as sudden collapse, which can significantly affect operations. Unfilled, out of use tanks can also accumulate groundwater, leading to potential environmental liabilities.
The Solution
CJGeo proposed 30lb/cuft CJFill-Ultra Lightweight (CJFill-UL) to fill the tank. CJFill-Ultra Lightweight is easily hand and machine excavatable to ensure that when the tank is removed in a few years that it’s not difficult.
While easily hand excavatable, CJFill-Ultra Lightweight still provides more than adequate compressive strength. In this case, total loads were just a few hundred pounds per square foot, whereas the CJFill material provides more than 17ksf of unconfined compressive strength. The American Concrete Institute publishes a removability modulus calculation which helps to quantify the ease of removal of controlled low strength materials, read more about it and how it relates to cellular concrete here.
It took CJGeo less than an hour to completely fill this tank. Confirmation of complete fill was uniform material venting from the tank vent ports.
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Tunnel Adit Fill
The Job
This tunnel adit fill project is part of the Purple Line project outside of Washington, DC. Specifically, the adit is located at the pedestrian connection between the Purple Line project and WMATA’s Bethesda station on the Red Line.
The Challenge
Plans call to connect the Purple Line to the Red Line using an adit constructed during the original construction of the Red Line. The adit is approximately 30 feet wide by a 35 foot tall arch. During preparation to blast from a shaft dropped adjacent to the station, a fault was identified passing through the adit.
The construction and design teams were concerned about stability of the adit during blasting operations as the Purple Line access tunnel was excavated towards it. The team determined that filling the adit to plug and stabilize it during blasting would be the most risk appropriate move.
Filling the adit would fulfill the design challenge of stabilizing the rock during blasting. However, it created the following challenges:
- the tunnel adit fill material would need to be removed after blasting was completed
- the adit is approximately 100 feet below grade
- there is very limited space up top
- material couldn’t segregate, and had to be pumped approximately 250 feet in addition to the 100 foot drop
The Solution
The tunnel engineer of record recommended CJGeo to the contractor. The EOR is familiar with CJGeo’s cellular concrete generation and placement expertise, and thought that cellular concrete would be the lowest risk way to fill the adit, while facilitating excavation and removal afterwards.
CJGeo took five days onsite to fill the adit, in lifts up to eight vertical feet. Due to the potential dead load from the rock cover, 400psi CJFill-Standard was the material of choice. By using our colloidal mixing dry batch process, the material set off quickly, ensuring that it would not consolidate during cure as lower energy mixing methods can suffer from.
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Virginia Lightweight Fill
The Job
This Virginia lightweight fill installation is located Norfolk, Virginia. The placement is part of a low income housing development in an area subject to flooding. The site is located a few blocks from downtown Norfolk.
The Challenge
Like many coastal cities, much of the ground in Norfolk is infill. On this site, fill material was entirely uncontrolled. It included construction debris, organics, and silty sands. In order to bring the finish floor elevations above flood elevation, the site needed to come up by nearly eight feet in some areas.
The Solution
CJGeo worked with the structural engineer to design a lightweight backfill program that would help reduce anticipated settlements. After stone columns were installed across the site, the CMU building walls were built on poured footings. After the walls were in place, CJGeo filled the entire building pads with Ultra Lightweight CJFill, with an average density of 25lb/cuft.
CJGeo batched CJFill-Ultra Lightweight with a 80psi at 28 day minimum compressive strength using the dry batch process onsite, and placed at times more than 1,000 cubic yards per day.
Once the CJFill-Ultra Lightweight was in place, plumbers trenched in plumbing, and placed twelve inches of sand on top of the CJFill-Ultra Lightweight. The work took around two weeks, using the dry batch generation method.
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Basement Wall Load Reducing Fill
The Job
This basement wall load reducing fill project is located in Lexington, Virginia, on a campus of Washington & Lee University. The scope is part of a new academic building construction project. The building will house the Williams School of Commerce, Economics & Politics.
The Challenge
The building is on a sloping site. The front of the building will be slab on grade, and the back half of the building will be a walk-out basement level. The transition between the two floors is an approximately fifteen foot tall wall with two 90’s.
The basement wall is designed to be braced by the floors and building. However, the floors & building couldn’t be built until the wall backfill was in place. In order to backfill the wall, it would need load reducing fill, or it would need temporary bracing.
The Solution
A structural engineer recommended the general contractor reach out to CJGeo about backfilling the wall with CJFill-Ultra Lightweight low density fill. Working with the structural EOR, geotech EOR & general contractor, CJGeo developed a backfilling plan that would allow backfilling the wall over three days while eliminating the need for temporary bracing.
CJGeo poured three lifts, each about 4.5′ deep. A dry batch process plant running at up to 200 cubic yards per hour and using preformed foam from Aerix Industries backfilled the wall in three days.
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Low Density Bridge Underfill
The Job
This low density bridge underfill project is located on Interstate 95, in Philadelphia, Pennsylvania. The scope is part of a large widening and reconstruction project. The bridge is located over Carver Street, just south of the Tacony-Palmyra Bridge.
The Challenge
As much underfill as possible had to be in place prior to the bridge demolition. Otherwise, it would have been impossible to demolish the deck, beams & other structures during a limited closure. There are also multiple underlying utilities which would not tolerate the nearly 5ksf of additional dead load from using traditional flowable fill.
The Solution
In order to fill up to the bottom of the beams, CJGeo designed a mass fill placement plan that stepped in at a roughly 1.5H:1V slope. CJGeo batched CJFill-Ultra Lightweight with a 40psi at 28 day minimum compressive strength using the dry batch process onsite, and placed at times more than 1,000 cubic yards per day.
Once the CJFill-UL was in place to complete this low density bridge underfill, the customer was able to demolish the bridge and beams, only need to bring in a few feet of crushed stone for the pavement base, and then pave the roadway to restore traffic. This was performed during an accelerated closure to minimized traffic disruption. The work took around two weeks, using the dry batch generation method.
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Lightweight MSE Wall Backfill
The Job
This MSE wall lightweight backfill project is located near Chester, Virginia. The MSE wall is part of a ramp reconfiguration and lengthening project at the interchange of Rt 10 and Interstate 95. Specifically, this ramp is from westbound Rt 10 to northbound Interstate 95.
As part of the ramp lengthening and realignment, the ramp needed to shift out onto an existing embankment.
The Challenge
There was insufficient right of way to widen the embankment without acquiring additional right of way. In order to shift the road without acquiring additional land, the geotechnical engineer of record, Schnabel Engineering, recommended to building a mid-slope MSE wall. The wall design includes a lightweight reinforced and retained zone to eliminate any net change in load. Effectively, when the slope is notched for the MSE wall construction, the difference in fill density allows for increased height.
The Solution
The existing soils were rough 125lb/cuft, and the CJFill-Ultra Lightweight backfill is 30lb/cuft. This allows for two additional feet of fill depth for every foot of undercutting. The final MSE wall lightweight backfill design included a 140psi minimum 28 day compressive strength (ASTM C495).
It took three lifts to backfill the wall, which was at most eight feet tall, and roughly 150 feet long. A composite drain on the slope addresses and water migration through the soil slope, and ties into a gravel bed at the base of the CJFill-UL load reducing fill.
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Massachusetts Lightweight Fill
The Job
This Massachusetts lightweight fill project is located at Boston’s Logan International Airport. It is part of Logan Forward continuing improvements to the airport.
The Challenge
As part of this project, the general contractor installed two cast-in-place barrier walls. The space between the barrier walls is between four and nine feet. The walls are curving, have non-vertical faces, and bear on a curving, non-horizontal existing podium slab. The gap between the walls needed to be filled in order to pour a housekeeping slab spanning between the walls.
This work is all on an existing podium structure. So, the fill density between the two walls had to be as low as possible.
The Solution
CJGeo proposed filling between the two walls with CJGrout 20SDB. 20SDB has a similar density and compressive strength to typical expanded polystyrene (EPS, or Geofoam) blocks. However, unlike geofoam blocks, 20SDB:
- is pumped, so doesn’t require trimming, and fits to any shape
- expanded onsite, so logistics are significantly simpler
- cures within a few minutes, so is still quick
- not affected by petroleum products
A CJGeo polyurethane grouting crew took a single shift onsite to install the 64 cubic yards of CJGrout 20SDB. The general contractor began installing the topping slab the next day.
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New Jersey Lightweight Fill
The Job
This New Jersey lightweight fill project is located in Secaucus, New Jersey. It’s part of a two building, wood framed multifamily structure over a concrete podium. The site is located very close to the Hudson River, so the underlying soils are poor, and there is a high likelihood of future flooding. As a result, the ground was improved using rammed aggregate piers, but then needed to be brought up approximately 2′ above existing grade.
The Challenge
Rammed aggregate piers were only able to improve the site soils so much. To avoid the costs of rigid inclusions or piles, the design team had to reduce the load applied by the backfill needed to elevate the site. The maximum unit weight was 30lb/cuft, and because of potential flooding, the material had to be permeable, in order to reduce uplift potential.
The Solution
CJGeo proposed using 25lb/cuft CJFill-High Permeability to backfill the stem walls, to bring the building pad up approximately two feet. 25lb/cuft CJFill-HP is provides excellent bearing capacity, but is hand excavatable.
Hand excavatability was important on this project. There was extensive under slab plumbing required, and the lightweight fill couldn’t impede on its installation. A great advantage of 25lb/cuft CJFill-HP is that it provides a clean, stable working surface that easily supports mini and mid-size excavators.
CJGeo mobilized a wet batch cellular concrete plant crew to the site. The crew used silt fence to break the roughly 80 thousand square foot pour into roughly 150CY placements. Each individual pour on this New Jersey lightweight fill project allowed the plumbing contractor to drive their mini excavators on it the following day. The plumbers enjoyed the clean, dry working surface.
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