Power Conduit Abandonment
THE JOB
This power conduit abandonment project was part of a new line installation project. A utility contractor installed a new, upgraded parallel line. After switching service, pulling the electrical lines, and removing the oil, the contractor had to completely fill the lines with grout.
THE CHALLENGE
There are very few access points for high voltage power conduits. There were multiple runs over 3,500LF on this project, and it was neither safe nor practical to excavate down to the line at the frequent intervals required to fill the conduit with flowable fill.
THE SOLUTION
CJGeo proposed abandoning the conduit with CJFill-Ultra Lightweight cellular concrete. Cellular concrete is exceptionally high mobility grout. It’s easily pumpable thousands of feet at a time, at low pressure. Through careful planning with the client, CJGeo broke down the placement into 9 different runs, ranging from 200LF to 3800LF. Each placement utilized existing access points, such as vaults & terminations.
CJGeo successfully completed each run of power conduit abandonment. Pumping pressures never exceeded 30psi, and uniform grout showed at the vent end of each run to confirm complete fill. The work was performed over the winter, including multiple placements below freezing, and during the snow. The cellular concrete was generated using Aerlite preformed foam, by Aerix Industries, and continuous generation wet batching.
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1 Mile 36″ Waterline Abandonment
THE JOB
CSX crews were surfacing the mainline track in Baltimore when the tamping equipment struck an object immediately below the ties. Investigation revealed that it was a manhole associated with nearly 6000LF of 36″ water main primarily running immediately below the tracks. The municipality relocated the waterline. Next, they had to fill the pipe from just two intermediate points. There were three sections of pipe; 1200LF, 1600LF & 2900LF. Various potential solutions for the watermain abandonment included:
- threading sacrificial tubing and grouting on the way out, and
- pumping flowable fill from the manholes,
However, none were economical or could guarantee a pipe abandonment below the railroad.
THE CHALLENGE
The project designer, OBG, identified cellular concrete as a potential solution to the problem and reached out to CJGeo to determine its feasibility. CJGeo confirmed the appropriateness of cellular concrete and set out to create a grouting plan. Coordination between the utility contractor and slurry provider (the site was too small to set up a batch plant) was crucial to ensure that the runs of pipe were all successfully filled in a single shot each. With train frequencies of 3-4 per hour, if the operation didn’t work and the pipes were only partially filled, there was no opportunity to create intermediate access points to finish grouting a section of pipe.
Based on the required bearing capacity and production requirements, CJGeo proposed 22lb/cuft CJFill-Ultra Lightweight cellular concrete for abandonment. With a 25psi break strength at 28 days, the mix provided the required strength, met the CSX utility occupancy standard for abandonment, and maximized expansion in order to ensure the longest run, which required nearly 1000CY of the finished product, could be grouting in a single shot.
THE SOLUTION
CJGeo mobilized a 150CY/hour cellular concrete crew to the site and performed the two shorter runs the first week. The project was broken into two different weeks due to the criticality of ensuring the longest run was filled completely without issue. The first two runs allowed CJGeo, the GC, railway flaggers, railway operations, and the slurry provider the opportunity to work out any kinks in operations during the lower risk placements.
The following Tuesday, starting at 0600, Chaney Enterprises delivered the first of 24 loads of slurry. Overall, the work took three days. CJGeo generated & pumped a total of 1710 cubic yards of cellular concrete to successfully complete the waterline abandonment.
This project would have been much easier using a mobile batch plant, which we now have three of.
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Fullerton Reservoir Annular Space Grouting
THE JOB
This reservoir annular space grouting project is located in Baltimore, Maryland. As part of the construction of a new drinking water reservoir for Baltimore County, Maryland, 140LF of 30″ jack & bore with a 12″ DIP water line and two 4″ PVC conduits required annular space grouting.
THE CHALLENGE
Due to the relatively long run and delicate PVC carrier pipes, CJGeo proposed using foamed concrete for the annular space grouting. 45lb/cuft CJFill-Standard cellular concrete generated using Aerlite preformed foam was proposed to achieve the owner’s requirement of 250psi at 28 days.
Carrier pipe buoyancy control is one of the most difficult elements of small diameter annular space grouting. In very large diameter placements, multiple lifts are practical, but in small diameter pipes, generally aren’t possible. When multi-lift grouting isn’t practical, having a grout density less than water (about 60 pounds per cubic foot) facilitates single lift grouting as long as the carrier pipes are full of water.
THE SOLUTION
In a short morning, they generated and placed 31 cubic yards of CJFill-Standard cellular concrete to successfully grout the annulus. Peak pumping pressure was less than 5psi. Confirmation of a complete fill was uniform material discharging from the 12 o’clock vent at the opposite end from placement.
Because the grout density was significantly less than the density of water, filling the carrier pipes with water controlled all buoyancy.
28 day breaks confirmed that CJGeo exceeded the break strength requirement.
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MD 355 Lightweight Fill
THE JOB
As part of the construction of a pedestrian underpass at the Medical Center WMATA station, an open cut tunnel was installed. The tunnel crossed under MD-355, but over the underlying Metro Red Line tunnel. To maintain vehicular traffic during construction, a temporary bridge sat across two H-pile & lagging open cut walls.
After the tunnel was completed, the 7′ of space between the top of the new pedestrian tunnel and the bottom of the temporary bridge had to be filled. Numerous utilities, including:
- gas transmission mains,
- a power vault & duct bank,
- municipal water,
- gravity sewer,
- and numerous communication duct banks and lines,
All passed through the fill area. The tunnel designers needed lightweight fill material for the majority of the backfill to reduce loads on the new pedestrian tunnel.
The extensive utilities and limited working space made other lightweight fill materials. Alternates, such as EPS blocks and lightweight aggregate, were impractical to place. The Clark Foundations project team reached out to CJGeo to come up with a pumpable, self-consolidating lightweight fill solution.
THE CHALLENGE
CJGeo proposed using 30lb/cuft CJFill-Ultra Lightweight cellular concrete for the lightweight backfill. Cellular concrete had a few distinct advantages:
- Unit weight: the 30lb/cuft density met the designer’s requirement for unit weight. Low density grout also significantly reduces encased utility buoyancy during placement.
- Strength: the 125psi at 28 days strength far exceeded the requirement, and allowed for nearly immediate final backfill & paving
- Safety: time in the tunnel to set the grout placement pipes is minimal. No personnel are in tunnel during placement.
- Constructibility: aside from being lightweight, the primary concern was ensuring that all utilities were fully encapsulated. The fill had to go to within 12″ of the bottom of the temporary bridge beams. This would have been exceptionally difficult with any type of non-pumped lightweight fill.
THE SOLUTION
CJGeo mobilized a single low density cementitious fill crew to the site, capable of producing up to 150CY/hour of cellular concrete. Over the course of three days, CJGeo placed 990CY of 30lb/cuft non-pervious cellular concrete, using Aerlite preformed foam.
7 day breaks on the cellular concrete exceeded the minimum strength for backfilling. This allowed the customer to stay on their targeted schedule.
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Communication Jack & Bore Grouting
The Job
The Sandston area, just outside of Richmond, Virginia, is at the crossroads of major north/south data transmission lines, and transoceanic data transmission lines. This jack & bore grouting was done to support a road crossing connecting two new data centers.
The Challenge
As part of the construction of a new, multi-billion dollar data center, a utility contractor bored two, 48″ steel casings under a roadway & adjacent wet utilities for a road crossing. Each of the casings had up to 20 different PVC conduits held in place using casing spacers. The contractor needed a grout that could be placed at minimal pressure while ensuring complete fill without damaging the conduits.
To avoid carrier pipe buoyancy, the maximum allowable grout density for the annular space grouting was 45lb/cuft.
The Solution
CJGeo mobilized a cellular grouting crew to the site and did the jack & bore grouting on both pipes in a single day. The peak grouting pressure was 5psi, and confirmation of fill was achieved when uniform cellular concrete was vented from the 12 o’clock position on the opposite end of each bore. 38PCF CJFill-ST was used to achieve the design strength of 200psi at 28 days.
CJFill-ST is heavier than CJFill-Ultra Lightweight, which is the most common cellular grout that CJGeo uses for annular space grouting. However, in the case, the municipality specified a higher compressive strength due to the proximity of multiple other critical utilities.
CJGeo used wet batch on this project due to the low volume and proximity of a ready mix plant. Wet batch typically has lower peak heat of hydration, which is helpful when grouting around PVC.
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Microtunnel Annular Space Grouting
The Job
This microtunnel annular space grouting project is part of a massive interstate expansion project in Charlotte, North Carolina. Seven micro tunnels were mined under I-77 to convey various utilities below the highway. Microtunneling was used, with casing diameters of 60″, along with a hand-mined tunnel lined with an 84″ tunnel liner plate.
Due to the length of runs, volumes required and strict NCDOT mix design requirements, the tunneling contractor reached out to CJGeo to explore cellular concrete as an option for the microtunnel annular space grouting.
The Challenge
CJGeo proposed performing the annular space grouting using 30lb/cuft cellular concrete. CJGeo has approved NCDOT mix designs for cellular concrete, which helped facilitate expedited submittal processing.
Cellular concrete was also advantageous from a carrier buoyancy perspective. The carrier pipes installed in each of the tunnels were all negatively buoyant in the grout. This helps to ensure proper alignment and minimize any chances of damage during grouting.
The Microtunnel Annular Space Grouting Solution
During the first mobilization, CJGeo placed 630CY of CJFill-Ultra Lightweight cellular grout to grout the two tunnels over a period of three days. The 60″ tunnel was grouted in a single lift, the 84″ tunnel was grouted in two lifts.
Confirmation of complete fill was through venting of uniform cellular concrete at the far ends of each tunnel. Additionally, the 84″ tunnel liner plate structure had cellular concrete weeping out of the bulkhead on the exterior of the plate. This indicates that the cellular concrete had exfiltrated through the liner plate joints and was flowing outside of the liner plate.
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Tampa Microtunnel
THE JOB
As part of a large design-build utility rehabilitation and capacity improvement project, a 60″ micro tunnel was dug under an interstate. The tunnel was approximately 40 feet below grade, and 1050LF. Due to the length of the tunnel, traditional grouts were unlikely to be successfully placed for the annular space grouting. Concerns with traditional grouts included flowability, carrier pipe buoyancy, and high pumping pressures, compounded by a local shortage of flash, which was a critical component of the planned grout.
The tunneling contractor reached out to CJGeo to see if cellular concrete would be a feasible product for the annular space grouting. The project was located near Tampa, Florida.
THE CHALLENGE
CJGeo proposed cellular grout to avoid the challenges associated with fine aggregate based grouts. To meet the 1,000psi requirement at 28 days, CJGeo proposed a 60lb/cuft CJFill-Standard, generated using Aerlite preformed foam, and continuous generation.
Cellular concrete provided a few key benefits for this project:
- material supply–cellular concrete does not require fly ash in order to be highly mobile and pumpable
- low unit weight–by being less dense than water, cellular concrete does not cause the water-filled carrier to be buoyant
- flowability–cellular concrete is very highly mobile
- economics–the 400CY project volume would take two days
THE SOLUTION
CJGeo mobilized a cellular concrete crew to the site. Using continuous generation and slurry from a local ready-mix supplier, CJGeo grouted the annulus completely. Completeness of fill was verified by uniform material venting from each of the vent and placement pipes at both ends of the tunnel.
Peak pumping pressure during grouting was approximately 8psi when grouted through the annulus. CJGeo did this project before we began using mobile dry batch foamed concrete plants. Dry batch generation would facilitate this placement taking a single day instead of two, which significantly reduces risks.
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