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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NY Thruway HDD Annular Space Grouting
The Job
This HDD annular space grouting project is east of Buffalo, New York, under the New York Thruway. As part of distribution improvements, National Grid’s contractor bored 830LF through rock using HDD. The bore was 30″, with a 16″ HDPE casing, carrying three, 4″ HDPE conduits.
As part of the installation, the NY Thruway Authority call for casing back grouting, and the casing pipe’s annular space grout filling.
The Challenge
The proposed back-grout had to be:
- pumpable 830LF at very low pressure,
- dense enough to displace the 10 pound per gallon drilling mud, and
- provide sufficient strength to meet Thruway requirements.
The proposed annular space grout had to be:
- pumpable 830LF at very low pressure,
- light enough to not apply excessive pressure on the conduit pipes, and
- also provide sufficient strength to meet Thruway requirements.
The Solution
CJGeo proposed two different grout mixes to meet the project requirements. 85lb/cuft CJFill-Under Water casing backgrout for the displacement of the 10PPG (75lb/cuft) drilling mud. And 25lb/cuft CJFill-Ultra Lightweight annular space grout within the casing.
CJGeo’s crew mobilized to the site, and successfully performed the back-grouting and annular space grouting in a single day. A tremie pipe strapped to the HDD casing was used for the back grouting. By pumping the 85lb/cuft (11 pound per gallon) CJFill-Under Water to the low point, the drilling mud was floated out of the reamed hole annulus.
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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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MSE Wall Lightweight Backfill
The Job
This MSE wall lightweight backfill project is located near Richmond, Virginia. The geotechnical investigation for a double bridge replacement in Amelia County, Virginia found a layer of compressible soils below four proposed abutments.
Anticipated settlement exceeded allowable settlement, so the abutments were designed to be backfilled with expanded shale lightweight aggregate.
The two parallel bridges have an AAWDT of 14,000. They carry a rural divided highway (US-360) over Norfolk Southern Railway & Business 360 in Amelia Courthouse, Virginia.
The Challenge
Lightweight fill placement had to be unaffected by frequent rail traffic, have a limited footprint, and be economical. The anticipated settlement at design was 2.5 inches. A challenge arose during construction mobilization due to Covid-related issues. There was nowhere to stockpile the lightweight aggregate onsite. But the trucking market was so unreliable, that the material needed to be staged onsite. This was to ensure continuous MSE wall construction.
The Solution
CJGeo provided a value engineering proposal to utilize 30lb/cuft CJFill-Ultra Lightweight cellular concrete in place of the expanded shale lightweight aggregate. This significantly reduced the unit weight of the lightweight fill. Given the 70lb/cuft density used in the design, further reducing the anticipated settlement.
CJGeo mobilized a 200CY/hour low density controlled low strength material (LD-CLSM) plant to the site and placed lifts ranging in size from 35 to 300CY. Wall erection crews were able to walk on the in-place cellular concrete without leaving footprints as quickly as 4 hours after each placement.
The total project volume was approximately 7200CY.
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Upham Brook Annular Space Grouting
The Job
This Upham Brook annular space grouting project is located in central Virginia. A sewer trunkline expansion in Richmond, Virginia required five bored road crossings ranging from 60″ to 72″.
Tunnel lengths are from 200LF to nearly 600LF. Mining is through rock using slurry micro-tunneling. One tunnel had mixed face conditions, which was unanticipated.
The design engineer required cellular concrete for annular space grouting due to run length, and buoyancy control of the carrier during grouting.
The Challenge
Not many; the longest run on this project, 600LF is a relatively short distance to push cellular concrete. Three of the four tunnels are round. The fourth tunnel is a combination of a round, MTBM-mined tunnel that transitions to a hand mined arch. The hand mine arch was to rescue the MTMB, which became stuck under a triple track CSX rail line. There was very poor access (the rescue shaft is in the CSX right of way).
The Solution
CJGeo proposed 38lb/cuft non-permeable CJFill-Standard low density controlled low strength material to meet the designer’s 200psi 28-day compressive strength requirement.
Over four different mobilizations, CJGeo successfully placed approximately 900CY of annular space grout.
The LD-CLSM generation was wet batch. Wet batch generation was chosen due to the relatively small daily volume of material placement and very tight sites.
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Stone Arch Lightweight Backfill
The Job
This stone arch lightweight backfill project is located in Somerset, New Jersey. The stone arch bridge, constructed in the 1800s, was experiencing significant scour at the bases of the arch. This caused differential settlement of the structure, and deterioration of the wing walls.
The bridge is adjacent to a historic mill structure. Due to historic preservation requirements, the structure had to be maintained in kind, as opposed to replaced.
The bridge was originally bearing on shallow stone foundations.
The Challenge
As part of rehabilitating the structure, structural engineers designed two new mass footings in the stream bed to underpin the edges of the stone arch. Then, to strengthen the arch designed a 12″ thick reinforced concrete arch overlay on top of the stone arch for the full length/width of the bridge.
In order to compensate for this additional weight, designers determined that a lightweight fill material was needed to reduce the chances of inducing settlement.
Designers also evaluated remedial deep foundations but determined that lightweight fill was the fastest and most economical solution.
The Solution
After the structure had been rehabilitated, CJGeo installed 325CY of 30lb/cuft CJFill-Ultra Lightweight to complete the stone arch lightweight backfill installation. Placed in lifts up to 4 feet thick, the work was took just three days.
By using 30lb/cuft closed cell cellular grout, the dead load on the underlying soil decreased by up to 935lbs/sqft relative to compacted soil backfill.
Cellular concrete is self-consolidating and pumpable hundreds of feet. Therefore, single side access was not a problem, and no compaction equipment was necessary.
A crew of two workers completed the pour using continuous wet batch generation. CJGeo chose wet batch generation due to the relatively small daily volume of material placement.
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I-66 Annular Space Grouting
The Job
During the widening of Interstate 66 near the interchange with US-15, nine new culverts were installed by jack and bore, and one via direct jacking. The carrier pipes were a mix of spiral metal, precast concrete, and corrugated HDPE, and ranged in length from 150 to 350 feet.
The Challenge
The contractor, who was responsible for grouting, was concerned about carrier pipe buoyancy during grouting, and also run length. All work had to be done from one side of the interstate highway (three lanes in each direction, plus full-width shoulders and a median strip), as there was no access on the far side.
The Solution
CJGeo proposed 30lb/cuft CJFill-Ultra Lightweight cellular concrete for the annular space grouting mix design. Cellular concrete is the preferred material for annular space grouting because it is highly flowable, and reduces the chances of damage to carrier pipes in long placements. Its low unit weight also reduces carrier pipe buoyancy. CJGeo placed 350CY of cellular grout to successfully complete the jack and bore annular space grouting over three different mobilizations.
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Virginia Annular Space Grouting
THE JOB
1100 feet of pile-supported 34″ PCCP water line over a drinking water reservoir was being slip-lined. This Newport News, Virginia annular space grouting project was specified by the designer to use cellular concrete. The relining contractor used 30″ welded HDPE for the slip line, which then required annular space grouting.
There were multiple leaks at the joints between the PCCP sticks. Work was complicated by a seasonal light display, which limited access hours to the job site.
THE CHALLENGE
The designer specified 55PCF wet cast density CJFill-Standard cellular concrete for the annular space grouting. Cellular concrete is highly flowable. High flowability ensures low installation pressure, reduces flotation of lightweight carrier pipes, and ensures complete void filling outside of the host pipe. Using cellular concrete for annular space grouting was specified by the HDPE slip lining pipe manufacturer. Buoyancy control was by water fill of the carrier pipe.
Nearly every joint on the pipe was leaking. Each joint had to be grout tight prior to starting the grouting process.
THE SOLUTION
All venting was over water. CJGeo completed this Virginia annular space grouting project without introducing any contaminants to the drinking water reservoir.
The 55PCF cellular concrete provided a break strength of approximately 700psi at 28 days. Peak installation pressure was 18psi. The crew used wet batch generation due to the relatively low volume.
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Maryland Annular Space Grouting
THE JOB
A jack & bore contractor performed a 200LF, 54″ bore under an arterial highway. After sliding in a 48″ RCP carrier pipe (stormwater), the annular space required grouting. This Maryland annular space grouting project is located in Jessup.
THE CHALLENGE
Due to size limitations, only one end of the pipe was accessible for grouting. The length of the placement was approximately 200LF, so grout had to travel 200LF at low pressure while ensuring a complete fill.
THE SOLUTION
CJGeo proposed cellular concrete for the annular space grouting. Cellular concrete is highly flowable. High flowability ensures low installation pressure, reduces flotation of lightweight carrier pipes, and ensures complete void filling outside of the host pipe.
CJGeo successfully performed this Maryland annular space grouting project in a single day using CJFill-Ultra Lightweight cellular concrete. The peak pressure at the pump did not exceed 5PSI throughout the project.
Due to the relatively low volume, CJGeo used continuous wet batch generation for making the cellular concrete. With continuous wet batch generation, a ready mix company delivers the slurry. The ready mix truck discharges into a grout pump, and CJGeo injects the preformed foam continuously in line downstream of the pump.
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Emergency Pipe Abandonment
THE JOB
The pavement of a rural road outside of Williamsburg, Virginia collapsed suddenly. The pavement was adjacent to a golf cart tunnel, but there was nothing apparently wrong with the cart tunnel. VDOT closed the road to perform exploratory excavation. The exploratory excavation revealed a partially-collapsed RCP culvert pipe running adjacent to the golf cart tunnel. This required emergency pipe abandonment.
THE CHALLENGE
CJGeo had to mobilize with very little notice. The proposed grout had to have the ability to flow through the unknown obstructions in the collapsed RCP, and also out into any voids outside of the collapsed pipe.
THE SOLUTION
CJGeo proposed 30lb/cuft CJFill-Ultra Lightweight cellular grout due to its highly flowable characteristics. Cellular concrete is excellent for ensuring complete fills of collapsed or compromised pipes.
CJGeo mobilized to the site within one day and completed the emergency pipe abandonment in less than two hours. The road was opened back up to traffic immediately afterward.
The 30lb/cuft CJFill-Ultra Lightweight cellular grout that CJGeo placed on this project has an average strength of around 150psi at 28 days. However, it will accept foot traffic and equipment traffic within 12 hours. In this case, the collapsed pavement had already been reconstructed after the compromised pipe was identified. The Aerlite preformed foam was from Aerix Industries.
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