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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Yonkers Polyurethane Grouting
The Job
This Yonkers polyurethane grouting project is located in Yonkers, New York. The project is part of a renovation of a multi-tenant strip center into a single discount grocery tenant.
The Challenge
During construction, someone on the general contractor’s team thought that areas of the floor sounded hollow. Tapping on the floor, it sounded like a drum. The contractor reached out to CJGeo, and we recommended performing a few cores in the hollow sounding areas.
Coring revealed extensive voids in two areas of the building footprint. Both were along the side exterior walls. In one area of the floor, the voids were up to 4′ deep. The apparent cause for the voids was a longstanding problem with below slab plumbing when the space was a deli and dry cleaner.
The Solution
After the cores were used to confirm the size and extent of the voids, CJGeo recommended CJGrout 20SDB geotechnical polyurethane grout to fill the voids.
CJGrout 20SDB is ideal for filling large voids below floors because it is low exotherm. Many foams used for polyurethane grout are not well suited for filling very large voids.
A plumber installed new sanitary lines below the floor after CJGeo completed the void filling. The void filling only took a single day onsite. It’s important to fill voids first so that cutting new plumbing trenches doesn’t cause catastrophic, unexpected settlement.
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USACE Pipe Abandonment
The Job
This USACE pipe abandonment project is located in Muncie, Indiana. The project was part of a locally-administered stormwater improvement project. Because the pipes pass through a US Army Corps of Engineers levee, abandonment of the existing culverts had to be performed to USACE specifications.
The Challenge
New pipes and an endwall wall had been in place for a few months. All paving restoration was done, and the original pipe discharged through the new endwall. Specifications for USACE pipe abandonment call for cellular grout with a minimum of 300psi unconfined compressive strength at 28 days, 100psi penetration resistance at 24 hours, and minimum wet cast density of 45lb/cuft (CJFill-Standard).
The Solution
The contractor reached out to CJGeo due our expertise in cellular concrete placements with tight specs and discerning owners.
CJGeo mobilized a wet batch cellular grout crew to the site, and filled the two pipes in about an hour. Aerix Industries supplied the Aerlite-iX preformed foaming agent. Wet batch method was best due to the relatively low volume of the placement. Both runs of pipe are 36″ CMP. The first run is 73 feet, the second run 103 linear feet, for a total of 47 cubic yards.
CJGeo successfully filled the two runs of pipe. Confirmation of fill was venting of uniform grout out of the 6 & 12 o’clock ports on each end of both runs.
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Tunnel Shaft Sinkhole Grouting
The Job
This tunnel shaft sinkhole grouting project is located in Newport News, Virginia. It is located outside the gate for Pier 2 at Newport News Shipbuilding, home to the deactivated USS Enterprise (CVN-65). As part of water and sewer upgrades in the area, multiple shafts were excavated to facilitate guided pilot tube bores.
The Challenge
At a shaft in the middle of an intersection, the dewatering well driller was unable to maintain circulation. This resulted in incomplete dewatering points. During excavation of the ring beam and liner plate shaft, the floor blew out after excavating through a fat clay layer. The fat clay is underlain by a highly permeable flowing sand.
When the floor blew out, the shaft, which is roughly 30 feet diameter, settled up to a foot on one side, and the shaft flooded in a few minutes. Multiple large sinkholes opened up around the perimeter of the shaft.
The Solution
The utility contractor, who was sinking the shaft, reached out to CJGeo for a solution. The only way to salvage the situation was to adequately dewater the site, which was even less possible due to the extensive voids around the shaft.
CJGeo visited the site, and made a few recommendations. First was to grade the site to direct the surface water away from the structure. There were multiple blocks of surface stormwater flowing directly into the area around the shaft. Second was to perform polyurethane compaction grouting around the entire structure to fill voids under the pavement and around the liner plates.
CJGeo mobilized a geotechnical polyurethane grouting crew to the site the following day. Using CJGrout 35NHV61, the crew filled approximately 70 cubic yards of sinkholes. Grout uniformly migrated through the liner plates, indicating that voids were continuous around the perimeter, and across the full depth of the shaft.
After CJGeo completed the grouting work, the dewatering contractor was able to successfully drop four wells around the shaft. By dewatering the underlying flowing sands, the contractor was able to resume excavating the shaft.
A few weeks after stabilizing the shaft, the two tunnels were successfully completed from the shaft. A CJGeo cellular grouting crew then grouted the annular space on both tunnels.
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NCDOT abandonment grouting
The Job
This NCDOT abandonment grouting project is located outside of Chapel Hill, North Carolina. The abandonment grouting is the final step in a gravity main replacement project. The scope requires filling 3,023 linear feet of 24″ RCP gravity sewer with NCDOT-approved flowable fill.
The Challenge
This gravity main runs entirely in a cross-country backwoods right of way. Along the alignment, there are a few road crossings, which require the NCDOT approved material.
Because the new pipe is in the same right of way, there are multiple locations where new and old pipe alignments cross. This breaks it into a collection of smaller runs, as opposed to one continuous run of pipe.
The Solution
If this was one continuous run of pipe, it would be a great candidate for dry batch generation cellular grouting. The 352CY project volume would only take about two hours to fill.
However, being broken into multiple, shorter runs in the middle of the woods, meant that wet batch equipment was more appropriate from an access and productivity perspective.
CJGeo mobilized a wet batch crew to the site, and it took them two days to complete the work. There were a total of 11 runs of pipe and six placement points. The longest run was 1113 linear feet, the shortest only 56.
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NCDOT pipe abandonment
The Job
This NCDOT pipe abandonment project is located outside of Wilmington, North Carolina. It is part of a large highway improvement project to improve capacity in the rapidly expanding southern coastal North Carolina area.
The Challenge
NCDOT requires grout fill for most abandoned pipes within their right-of-way. Traditionally this is done using flowable fill mixes. Using flowable fill for short abandonment is generally pretty simple.
However, this project has more than 100,000 linear feet of pipe ranging from 6″ to 36″ to fill. Most flowable fill mixes won’t go more than a couple hundred feet in best cast conditions. The utility contractor was looking at having to dig up to five hundred access points to place flowable fill. That’s incredibly time consuming and costly.
The Solution
The utility contractor reached out to CJGeo about performing the abandonment grouting on this project, using low density cementitious material (cellular concrete).
Due to the highly variable pipe diameters and run lengths, CJGeo proposed a mix of wet batch and dry batch cellular concrete generation.
Wet batch was used for the lower volume runs. Dry batch is best suited for large volume runs. Over the course of a few months, CJGeo mobilized multiple times to fill runs as long as a mile at a time.
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Facing a similar challenge to this NCDOT pipe 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.
Ohio Annular Space Grouting
The Job
This Ohio annular space grouting project is located in Akron. It is part of the Northside Interceptor, being constructed by Granite Construction. The total project budget is about $215 million, to construct 6,660 linear feet of 16.5′ diameter segmental liner tunnel.
While the main tunnel is single pass, there are multiple tie-ins to the structure. Some tie-ins are open cut, and another is a microtunnel. The microtunnel is 530 linear feet of 48″ pipe.
The Challenge
Plans call to grout the annulus between the carrier pipe and microtunnel casing with 600psi at 28 day material. A lean concrete mix to achieve this compressive strength would be significantly heavier than water. This can cause significant headaches managing carrier pipe buoyancy, as the heavier the grout, the greater the uplift during grouting.
The Solution
CJGeo proposed a 55lb/cuft CJFill-Standard mix to meet the compressive strength requirement, while minimizing carrier pipe buoyancy. Because the proposed material is less dense than water, filling the carrier pipe with water during the grouting process keeps the carrier pipe in place.
A CJGeo dry batch cellular grout crew placed 119 cubic yards of 55lb/cuft CJFill-Standard over two hours to fill the annular space in a single lift. Cellular concrete is also referred to as foamed concrete fill.
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Indiana Pipe Abandonment
The Job
This Indiana pipe abandonment project is located in Anderson. Anderson is in central Indiana, near Indianapolis. The project is a water main relocation out of a park.
The Challenge
Plans call for safe loading the pipe being replaced. It’s important to fill abandoned utilities to prevent them from being groundwater conduits, or eventually failing completely. This can cause significant amounts of settlement, and transport soils long distances, neither of which is desirable.
The Solution
Using traditional flowable fill would have required close to 10 access points to place material into the pipe. This would have torn up a bunch of the park that the pipe ran though, and taken quite a bit of time.
CJGeo proposed filling the pipe from a single access point near the middle, using CJFill-Ultra Lightweight cellular grout. The beauty of cellular grout for abandonment is that it’s pumpable thousands of feet. In this case, the first run was 770 linear feet. The second run was 488 linear feet.
It would be possible to grout the entire run in a single stretch, however there was already an excavation at this point to blind a connecting pipe, and there was a nearby fire hydrant.
CJGeo sent a dry batch plant to the site, and the grouting work took less than an hour of pumping to completely fill the pipe.
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New York Pipe Abandonment
The Job
This New York pipe abandonment project is located in Newburgh, New York. Newburgh is on the Hudson River, about an hour upstream of New York City.
The Challenge
As part of a sanitary sewer upgrade project, 5,399 linear feet of gravity sewer ranging from 6″ to 24″ was specified for grout filling. The highest volume run was a 1,022 linear feet continuous run of 24″ pipe. The longest run was 1,469 linear feet of 18 inch” pipe. Each run did have intermediate manholes, but most manholes were a few hundred feet apart.
The Solution
Traditionally, the customer would have dumped flowable fill in the manholes in an attempt to completely fill the lines by gravity. However, many of the manholes were off road, and some of them were hundreds of feet apart. This makes gravity discharge of flowable fill into manholes unreliable for ensuring complete fill.
CJGeo proposed performing the abandonment grouting using 30lb/cuft CJFill-Ultra Lightweight cellular grout. Since cellular grout will flow much further at nominal pressures, CJGeo was able to place through multiple manholes at once, which significantly reduced access requirements.
Due to the relatively low volume on this project, continuous wet batch was the best method for generating the cellular grout for this project. Wet batch uses slurry delivered by ready mix truck, with Aerlite-iX added downstream of CJGeo’s slurry pump.
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Facing a similar challenge to this New York pipe 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.
Indoor Pool Abandonment
The Job
This indoor pool abandonment project is located in West Virginia, at Concord University. A swimming pool built in the 1970’s was no longer in use, and had sat empty for years. As part of a renovation, the pool had to be filled in order to pour a slab and prepare the room for other uses.
The Challenge
Like many buildings in the mountains, the original site sloped. A retaining/basement wall passes through the building close to the deep end of the pool, whose sloped floor roughly follows the original grade of the site. The structural engineer had to concerns about backfilling the pool:
- increasing lateral loads on the adjacent basement wall if a heavy, granular material was used for the fill material
- causing settlement by filling the pool with material heavier than the water it was designed to hold, and which the underlying soils had seen for years
The original bid had two options: filling the pool entirely with 57 stone, or filling it entirely with 2lb/cuft EPS blocks.
The Solution
Geofoam blocks would have addressed both the axial and lateral load challenges. However, EPS would take a few weeks to import, cut, and place. 57 stone would have been least expensive, but increased lateral and axial loads beyond those of water.
CJGeo proposed a value engineered alternative to fill the bottom 70% of the pool with 25lb/cuft CJFill-Ultra Lightweight low density cellular fill (LDCF), topped with 57 stone, and then a new floor slab. The structural engineer, architect and owner all accepted the proposed change. The general contractor was excited to save weeks out of their schedule.
A single CJGeo dry batch cellular concrete crew performed the work over two days. The first lift, of 400 cubic yards took about two hours to place, and was roughly 6 feet deep. The second lift, around 350 cubic yards, also took about two hours to place. The day after CJGeo wrapped up, the general contractor was able to start placing the 57 stone on top of the CJFill-Ultra Lightweight fill.
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