Utility Tunnel Abandonment
The Job
This utility tunnel abandonment project is located in Wilmington, Delaware. Approximately 750CY of subbasement and utility tunnel had to be filled as part of a commercial building adaptive reuse project.
The Challenge
The structural engineer had two concerns:
- the slab over the basements were to be replaced,
- tunnel walls required bracing to demo the roof slab
- the density of the fill needed to be as low as possible to reduce the chances of inducing settlement.
The Solution
CJGeo proposed 25lb/cuft CJFill-Ultra Lightweight low density controlled low strength material. Low density controlled low strength material is a fancy name for cellular concrete. 25lb/cuft CJFill-UL has an average of 80psi compressive strength. Because CJFill-UL cellular concrete is very mobile, there were no issues with filling the tunnel from just a few access points.
With an average cured unit weight of 21lb/cuft, the using load reducing fill material saved approximately 1ksf in dead load relative to conventional fill materials. CJFill-Ultra Lightweight also provides sufficient strength to brace the walls to facilitate floor removal, and also provide adequate bearing capacity for the new floor.
It took a CJGeo cellular concrete crew two days onsite to fill the tunnel and subbasement. Onsite dry batching made up to 100 cubic yards per hour of the 25lb/cuft CJFill-Ultra Lightweight. Material placement was through 4″ cores and an exterior access areaway.
Other types of lightweight fill would have been much harder to install. Foamed glass aggregate or expanded shale aggregate would be practically impossible to compact given the low headroom. The density of expanded shale aggregate is also relatively high, so would not have offered the load savings that 25lb/cuft CJFill-Ultra Lightweight foamed concrete does. EPS is very lightweight, but is very labor intensive in this type of application.
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Power Station Pipe Abandonment
The Job
This power station pipe abandonment project is between Richmond & Lynchburg, Virginia, along the James River. Dominion’s Bremo Bluff Power Station was taken off line in 2019. As part of complete decommissioning, demolition and site restoration took place in 2022.
The Challenge
Power stations typically have extensive pipes for cooling water circulation. At Bremo Bluff, the buried cooling pipe network consists for four, four foot diameter pipes, connecting to a junction box. Total linear footage of the forty-eight inch pipes is about six hundred linear feet.
Due to the remote location, the demolition contractor knew that it would be difficult to get timely deliveries of the nearly 40 loads of flowable fill needed to fill the pipes.
The Solution
The demolition contractor reached out to CJGeo for consultation on the best type of flowable fill for the pipe abandonment work. CJGeo recommended 25lb/cuft CJFill-Ultra Lightweight. 25lb/cuft CJFill-Ultra Lightweight has a 28 day compressive strength (ASTM C495) greater than 50 psi. This met the owner’s requirements.
25lb/cuft CJFill-Ultra Lightweight is nearly 80% air content. Therefore, each twenty-five ton load of cement delivered to the site turns into nearly 150 cubic yards of finished product. Due to this on-site expansion, instead of needing nearly 40 loads of ready mix flowable fill, the work only needed two loads of cement.
CJGeo generated and placed approximately 300CY of CJFill-Ultra Lightweight cellular concrete to fill the junction box and pipes. CJGeo made all of the material over a few hours onsite, using dry batch generation.
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Lightweight Tank Foundation
The Job
This lightweight tank foundation installation project is located in Baltimore, Maryland. During an industrial facility expansion, a new blending tank was being installed at the top of a retaining wall. In addition concerns about lateral loading on the wall, the area is generally known to be built with uncontrolled fill over compressible soils, so settlement is a concern.
The Challenge
Due to the presence of industrial waste and debris in the area, light duty deep foundations such as helical piles are generally difficult to install. To avoid inducing settlement, the geotechnical EOR reached out to CJGeo for lightweight fill options to net out the increased weight of the mat foundation and blending tank.
Based on loads, CJGeo suggested a 25lb/cuft cellular grout with a compressive strength of at least 50psi. At this density, the engineer was able to balance all loads with a 4′ deep undercut. The undercut extended a few feet out around the perimeter of the tank foundation.
The Solution
First, the concrete foundation contractor excavated the pit. Then, CJGeo mobilized to the site and placed 110CY of 25lb/cuft CJFill-Ultra Lightweight cellular concrete into the pit. The lightweight tank foundation placement took less than an hour. The foundation contractor was able to start setting steel and forms the following morning.
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Tennessee Annular Space Grouting
The Job
This Tennessee annular space grouting project is located in Brentwood. Brentwood is part of the Nashville metro area, which is rapidly expanding. As part of large water main installation, a 970′ tunnel, ranging from 60 to 78 inch diameter was mined through a small mountain. To ensure long term service improvements, a 42″ DIP water line occupies the tunnel.
The Challenge
The tunnel support is wood lagging, which is not permanent. Therefore, the annular space requires grouting to ensure long term stability of the new water line and adjacent ground.
Because the Nashville market is so hot, it’s really hard to get any concrete deliveries, let alone specialty mixes. The tunneling contractor knew that they would be hard pressed to self-perform the grouting using flowable fill. This was if they could even get material. So, they reached out to CJGeo about performing the annular space grouting with cellular grout made onsite with one of CJGeo’s custom mobile cellular batch plants.
The Solution
CJGeo proposed and installed 25lb/cuft CJFill-Ultra Lightweight cellular grout for the annular space grouting. By generating material onsite directly from bulk cement, using a dry batch plant, the 425CY annular space grouting took fewer than five hours.
Buoyancy control on this project was very easy. Because CJFill-Ultra Lightweight cellular grout is so much lighter than water, filling the carrier with water was sufficient to ballast the pipe against uplift during grouting. No casing spacers or top blocking needed. The American Concrete Institute classifies CJFill-Ultra Lightweight as low density controlled low strength material.
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Georgia Annular Space Grouting
The Job
This Georgia annular space grouting project is located in Athens, Georgia. The project involves three tunnels connecting four shafts. Tunnel lengths range from 116LF of 700LF, with diameters between 58.5″ ID to 9×9 arch segments.
The Challenge
In order to keep the carrier pipe from floating during grouting, the maximum allowable grout density was 70lb/cuft, and the minimum compressive strength was 200psi. Material had to be highly mobile, to facilitate placement through the 700LF of tunnel.
The Solution
CJGeo proposed 38lb/cuft cellular grout to the tunneling contractor. Over a period of three days, CJGeo batched and placed 1320CY of CJFill-Standard. Batching was performed utilizing an onsite dry mix plant, which was fed directly by bulk cement trailers. The minimizes the required laydown area on a very tight site.
Because of the very low grout density, the carrier pipe buoyancy control was simply water filling.
To address the transition from a round tunnel to an arch tunnel, CJGeo worked with tunneling contractor to design a sacrificial pipe venting system.
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30k CY Lightweight Embankment
The Job
As part of the redevelopment of the Sparrows Point industrial area of Baltimore, three bridges were to be replaced. The owner specified lightweight embankment techniques due to extensive compressible soils. Sparrows Point is undergoing a transition from a brownfield site to a buzzing logistics hub. Multiple new distribution centers, berths and manufacturing facilities have driven an explosion in vehicle volume.
The Challenge
The original embankments are industrial byproducts over underlying compressible soils. As part of the reconstruction, the embankments needed to be widened and raised up to six feet to increase clearance below the bridges for both highway and rail traffic.
Due to the underlying compressible soils, there were concerns that the approximately 30,000 cubic yards of fill material needed would cause settlement.
Most material was immediately behind the new abutments, and helped to optimize the deep foundations by reducing axial & lateral loads.
The compressive strength for the material was 80psi, with a target density of 25lb/cuft.
The Solution
CJGeo proposed 25lb/cuft cellular concrete as a lightweight fill material buildable with locally-sourced materials to reduce transportation related risks and exposure to trucking shortages. Cellular concrete was several hundred thousand dollars less expensive than either Lightweight Expanded Shale Aggregate or Foamed Glass Aggregate. It also doesn’t require onsite stockpiling, and freed up the general contractor’s labor force to perform work other than placing aggregate.
CJGeo poured the lightweight embankment structures using 25lb/cuft CJFill-Ultra Lightweight cellular concrete over four mobilizations. Because CJFill-UL is so lightweight, all forming was silt fence. Silt fence facilitates complex curves, and is very economical. Side slopes were poured at 2′ vertical steps on 4′ horizontal insets.
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Low Level Outfall Abandonment
The Job
This low level outfall abandonment grouting project is located in New Jersey. The Round Valley Reservoir, in Clinton Township, New Jersey is a 2300 acre man-made drinking water reservoir. It serves extensive portions of New Jersey. It was constructed by damming up two openings in a naturally-curved mountain.
As part of a dam upgrade project, a 1400LF, 36″ inner diameter LLO pipe needed to be grouted to place it out of service.
The Challenge
The pipe had been previously blind flanged, 180′ below the lake surface. There was a single, 12″ riser pedestal. There were numerous significant challenges to face, including:
- 2GPM residual leak from the blind flange buried in 15′ of lake floor debris
- inability to push sacrificial pipes more than 500′ up the pipe
- remote site with limited ready mix service
The Solution
CJGeo worked with the general contractor, diving subcontractor, sacrificial grout pipe installation subcontractor, geotechnical and civil EORs, and the owner, to develop a single stage grouting plan to place approximately 350CY of 68lb/cuft CJFill-Under Water cellular grout from the downstream end.
Venting was achieved by installing a 4″ removable vent pipe from the pedestal riser. The vent pipe ran 180VF to the lake surface, terminating on a barge. There was only one opportunity to do the job correctly. Therefore, CJGeo had two fully staffed grout plants onsite, and had all cement and mix water staged in onsite storage. This was all prior to the start of grouting to avoid any material logistics disruptions affecting the work.
CJGeo placed the 68lb/cuft grout over a period of a few hours, leaving an intentional air pocket at the high end to capture infiltrating lake water long enough for the grout to set prior to seeing lake head.
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Sloped Pit Lightweight Backfill
The Job
This sloped pit lightweight backfill project is located in Western Virginia, at James Madison University. This work is part of the conversion the basketball arena at JMU in Harrisonburg, Virginia into a practice and competition facility for other sports.
The Challenge
An area of sloped stadium seating needed to be removed, and the mezzanine level floor extended over the sloped soil, which stayed in place, and onto a new wall at the toe of the slope. To reduce the likelihood of inducing settlement by adding up to 10 feet of backfill over the existing soils, the architect originally designed the backfill material as Expanded Polystyrene (EPS blocks). However, given the uneven soil slope, this would have been very challenging to install.
The general contractor reached out to CJGeo to see if there was a more practical load reducing fill.
The Solution
Working with the general contractor, architect and geotechnical EOR, CJGeo designed a backfill system that could be installed in fewer than six hours onsite, still provided a significant reduction in load, and cost significantly less than the foam blocks. The optimal product to meet the project criteria was 25lb/cuft CJFill-Ultra Lightweight low density flowable fill. CJFill-Ultra Lightweight has all the constructibility advantages of flowable fill, along with the following additional benefits:
- is made at up to 200CY/hour onsite
- provides up to 150CY of final material per load of raw material to the site
- applies minimal lateral pressure on adjacent walls during installation
- significantly reduces dead loads to underlying soils & structures
CJGeo generated the material onsite using dry batch generation, and placed the material in two lifts in order the limit the lateral loads on the new CMU wall during placement to 0.9psi.
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Rail Bridge Pier Stabilization
The Job
This rail bridge pier stabilization project is located adjacent to the Congaree National Park. This project was a capital repair to a bridge pier for a Class I railroad. The rail line serves the Port of Charleston, SC.
The Challenge
The Congaree River south east of Columbia, South Carolina frequently sees high flow events, inundating the surrounding low country. At the transition from timber trestle to a bridge, the first bridge pier was originally constructed of stone. The pier bears on a timber mat with timber pile supports. Over time, the river channel migrated and began to expose the timber substructure and scour below the pier.
The nearest road was more than four miles away through impassible swamp. So, all work had to be performed from the river. All material had to be pumped across the bridge, a distance of approximately 600 feet. Due to the compressive nature of the underlying materials, any backfill material needed to be as light as possible. But, due to the high likelihood of flooding, couldn’t contribute significant potential uplift.
The Solution
To address the scour, minimize additional load to the underlying soils, and ensure long term stability of the structure, a third party consultant designed a two tier sheet pile jacket for the structure. They specified the backfill material as 65lb/cuft cellular concrete for the lower segment. And, approximately 45lb/cuft cellular concrete for the upper segment.
CJGeo designed mixes which would meet these requirements:
- be pumpable 600LF,
- tolerate the high vibration environment from the more than 12 trains per day, and
- facilitate a short installation timeframe.
After the general contractor installed the first level of sheet piling and dewatered the area, CJGeo placed approximately 150CY of 65lb/cuft CJFill-Under Water material. Next came installation of the second, smaller diameter sheeting ring. CJGeo then filled the annular space between it and the necked down pier with 45lb/cuft CJFill-Standard material.
CJGeo generated and placed all of the CJFill low density controlled low strength material over a period of four days onsite.
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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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