Savannah Tunnel Abandonment
The Job
This Savannah tunnel abandonment job is part of the JW Marriott Plant Riverside conversion. It’s an adaptive reuse hotel project of a decommissioned power plant in Savannah, Georgia. As a thermal generation facility, there are extensive water tunnels below the structure. The cast in place tunnels are part of the piled foundation.
The Challenge
As part of the conversion from thermal power generation to luxury hotel, the tunnels posed a maintenance concern. Due to concerns about inducing settlement with traditional flowable fill, the designer specified EPS Geofoam blocks. These would have effectively eliminated loads, but were deemed impossible to install.
The Solution
Someone onsite had heard of foamed concrete, so reached out to CJGeo. CJGeo evaluated the layout of the tunnels, isolation methods from the river, and designed a mix which would ensure both complete filling of the structures without adding any additional load.
CJGeo placed approximately 930CY of 20lb/cuft CJFill-UL cellular concrete over a period of three days to complete the Savannah tunnel abandonment. Because CJFill-UL is highly mobile, demo debris from the access holes for building bulkheads was left in the tunnels, and encapsulated with the CJFill-UL.
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Nashville Basement Backfill
The Job
Nashville Yards is a block-wide new build project in downtown Nashville, Tennessee. With multiple underground levels of parking, this Nashville basement backfill excavation is more than 30′ below grade in spots. The excavation walls are a combination of blasted rock and soil nail walls.
The Challenge
The designer wanted to reduce lateral loading on the basement walls as much as possible. Due to the irregular face of the blasted rock & soil nail walls, lightweight aggregate would have been very difficult to install and compact, and would have applied lateral loads for the life of the structure. Flowable fill would have been easy to install, but applied too much lateral loading during installation if done in practical pour volumes.
The structural engineer determined that 25lb/cuft cellular concrete would be the best backfill material. The project volume was approximately 1500CY, and the maximum fill depth was 30′.
The Solution
CJGeo mobilized a mobile batch plant which uses colloidal mixing to the site. Due to the extremely high quality mixing, the crew placed CJFill-Ultra Lightweight up to 10′ deep per pour. This included three pours 10′ deep and 250CY each to complete this Nashville basement backfill project on time.
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Veranda St Bridge Infill
The Job
This bridge infill work was part of Maine DOT’s Veranda Street Bridge Replacement Project, in Portland, Maine. Using rapid bridge replacement, the project took a three span bridge and converted it to a single span bridge.
The Challenge
To manage settlement due to up to 80′ of underlying WOH material, lightweight fill was needed to infill two spans, and backfill the new abutments. The absolute lowest unit weight possible requirement led to a hybrid cellular concrete/EPS fill design. The bulk of the infill is EPS blocks. However, due to the irregular surfaces, piers, etc., and the need for a lightweight load distribution slab, cellular concrete was integral to the design.
The Solution
Over two mobilizations for the bridge infill, through snow and freezing temperatures, CJGeo placed 3200CY of 25lb/cuft CJFill-Ultra Lightweight cellular concrete for abutment backfilling and existing pier infills. Then, CJGeo placed 778CY of 30lb/cuft CJFill-Ultra Lighweight as a topping slab over the EPS fill masses.
To ensure high quality material and minimize weather-related risks, CJGeo used onsite batching to generate the material. A mobile batch plant custom built for generating cellular concrete mixes water and dry bulk cement onsite. The cement paste and foam blend continuously to generate a completely homogenous material. With a slump of around 11.5 inches, both densities of CJFill-Ultra Lightweight cellular concrete were able to flow around all of the existing structures and provide a void-free fill.
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Industrial Basement Abandonment
The Job
This industrial basement abandonment project is located in Southside, Virginia. As part of an adaptive reuse project of an abandoned industrial site, the former onsite power plant’s stacks were being rehabilitated. Multiple tunnels and basement rooms had to be completely filled.
The Challenge
Due to safety concerns, nobody could enter the basement. No as-builts were available. Camera inspection through holes cored in the ceiling showed significant numbers of passageways and obstructions. The fill material had to be:
- exceptionally mobile,
- placed in deep lifts,
- and as light as possible.
Fill density was a concern because the basement was up to 15′ deep. 150lb/cuft traditional flowable fill would have caused too much anticipated settlement. Settlement of the basement structure could potentially cause settlement or movement of the adjacent smoke stacks.
The Solution
CJGeo proposed 25lb/cuft cellular concrete for the lightweight fill material. Using onsite colloidal batching, CJGeo can place material up to 20′ deep in a single lift, without consolidation. Because CJFill-Ultra Lightweight is so lightweight, the entire 15′ deep basement fill dead load was the same as from just 2′ of traditional flowable fill. For this application, Aerlite-iX was the most appropriate cellular concrete foaming agent.
CJGeo mobilized a 150CY/hour dry batch plant to the site after staging 300 tons of cement onsite using our in-house cement pig & trucking operation. Over four days onsite, CJGeo place 2700CY of CJFill-Ultra Lightweight material to complete the industrial basement abandonment.
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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 foamed concrete 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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