Lightweight Plaza Fill
The Job
Lightweight plaza fill for a private age restricted high rise new build in Tysons Corner, Virginia. Tysons Corner was historically an office heavy area of Fairfax County, but this project, along with many others, is increasing the amount of residential real estate in the area.
The Challenge
To manage dead loads over the four story parking deck, while achieving a landscape design requiring up to five feet of fill, the designer specified 20lb/cuft CJFill-High Permeability cellular concrete for the plaza fill material. The material had to be permeable, and placed up to 600′ from the closest access point for a plant. The deck elevation is about 30′ above the laydown area.
The total square footage of placement needed to be around 17,000 square feet. EPS foam blocks were an alternative fill material. However, EPS would have been exceptionally time consuming and expensive to install.
The Solution
CJGeo mobilized a 200CY/hour dry batch plant and crew, who generated up to 500CY/day for placement via hoses and a boom pump to successfully fill the plaza areas. Total project volume for this lightweight plaza fill was approximately 2200CY.
All material is onsite from dry bulk cement, with zero exposure to the hit or miss ready mix concrete market. An onsite cement storage pig allows overnight raw material delivery and staging, to eliminate traffic disruption.
The 20lb/cuft CJFill-High Permeability Low Density Controlled Low Strength Material placement was formed by the site concrete contractor. After the CJFill-HP had set, the site concrete contractor poured exposed aggregate sidewalks directly on top of the CJFill-HP. Other areas of the deck were backfilled with engineered lightweight soil, and then planted with extensive landscaping.
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Hollow Abutment Filling
The Job
This hollow abutment filling project is located in Buckland, Massachusetts. Buckland is a small town on the east end of the Berkshires. The bridge conveys a rural highway over a drinking water impoundment. As part of a bridge rehabilitation for MassDOT, two hollow abutments were specified for filling. This would turn the structural approach/departure slabs into slab on grade. The alternative would have been to completely replace the structures. Filling them with traditional weight backfill would have caused significant settlement.
The Challenge
It was up to 30′ from the bottom of slab to the underlying soil which had originally been installed to backfill the abutments. The lightest possible material capable of providing sufficient support to the pavement was required. This would reduce the loads applied to the bridge from the backfill. Due to the very constrained access (a few cored holes through the deck, and a few square foot port cut into each abutment face), the lightweight material had to be self-consolidating (placed as a fluid).
Due to integrated beams for the structural slabs, there were 12 different individual pockets which were up to 2′ tall. Each had to be vent independently during the final lift. Four of were under live traffic because the road had to have one lane open at all times.
The Solution
CJGeo worked with the general contractor to formulate a plan to vent the individual pockets from outside of the open lanes. This helps to ensure a complete fill without requiring a complete road closure. Over the course of two mobilizations, CJGeo placed 2,840CY of 25lb/cuft CJFill-Ultra Lightweight to fill the abutments.
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Grain Silo Tunnel Backfilling
The Job
This grain silo tunnel backfilling project is located in Tampa, Florida. As part of a redevelopment project in downtown Tampa, Florida, a large grain milling facility was moving operations from the downtown port to a new facility further down Tampa Bay.
The Challenge
The facility is immediately adjacent to Tampa Bay. To minimize flood risks, the the entire structure is above grade. This includes the 8′ tall unloading conveyor tunnels. The structure was bears on a mat slab cast over thousands of auger cast piles. The unloading tunnels were only about 10% of each silos footprint. So, the areas long side of the tunnels needed to be filled.
Due to the slipform construction, there was very limited access. So the backfill material around the tunnels needed to be pumpable. Flowable fill was an option, but is very heavy. The design build contractor identified cellular concrete as a potential backfill material. This could save nearly 1ksf of dead load off of the mat foundation.
The Solution
CJGeo worked with the design builder to create a mix design that would minimize the amount of dead load on the foundation, while providing adequate support for the bin floor when fully loaded with grain. Over the course of a few weeks, CJGeo crews placed nearly 7200CY of 25lb/cuft CJFill-Ultra Lightweight cellular concrete. Rodbusters were able to start setting steel the day after completion of the final lift in each of the silos.
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9.5kCY MSE wall backfill
The Job
This MSE wall backfill project is located on Interstate 95 north of Baltimore, Maryland. The Express Toll Lanes will add extra capacity up the center of the existing roadway. This project is adjacent to a previous CJGeo project, where we placed 2,000 CY of CJFill-Ultra Lightweight cellular concrete as part of the Clayton Road Overpass reconstruction.
The Challenge
A 96″ diameter PCCP raw water supply line runs parallel to Interstate 95 along most of the project length. Originally, there was quite a bit of room between the roadway and the water line. However, as lanes are added, it’s gotten closer and closer to the PCCP water line. As part of this project, there are extensive ramp and embankment sections. They are immediately adjacent to the waterline, which is not in a condition to see any increase in loading.
To address this, designers specified lightweight material for the MSE wall backfill material.
The CJFill MSE Wall Backfill Solution
Originally designed for backfilling with Lightweight Expanded Shale Aggregate (LESA). CJGeo worked with the contractor to develop a hybrid MSE wall backfill material of 30lb/cuft cellular concrete and traditional weight 57 stone.
The relative depths of the two materials was selected so that the average density of the mass was equal to that of an entirely LESA backfill. This resulted in only needing roughly 2/3 the volume of lightweight backfill material.
Lightweight backfill is rarely less expensive as soil or traditional aggregates. However, by leveraging the very low unit weight of cellular concrete, a blended solution was possible that saved significant amounts of money.
CJGeo generated as much 500CY per day of CJFill-Ultra Lightweight to backfill the wall. The 30lb/cuft wet cast density provides adequate pull out resistance, and 140psi of unconfined compressive strength at 28 days.
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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 does. EPS is very lightweight, but is very labor intensive in this type of application.
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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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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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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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