Steam Tunnel Lightweight Backfill
The Job
This steam tunnel lightweight backfill project is located at Western Carolina University, in Cullowhee, North Carolina. As part of the expansion and renovation of the steam plant, a section of existing steam tunnel needed to be uncovered to install a new wall. The wall needed to be backfilled, and due to the condition of the tunnel, the lighter the backfill the better.
The Challenge
The site was exceptionally tight, and the location was more than 30 minutes from the closest ready mix plant. The backfill depth was nearly 15 feet, but the project was only about 1200CY. So, doing 2′ lifts would have been slow and expensive.
To effectively eliminate axial loads from the tunnel, the structural engineer designed a cardboard void form system to temporarily support precast planks on top of the tunnel, which was approximately 5′ wide and 5′ tall. The planks extended about 18 inches beyond the sides of the tunnel. The void forms were wrapped in plastic. This ensured they wouldn’t be fouled by the CJFill-Ultra Lightweight cellular concrete during the pour. After the CJFill-UL was in place, the ends of the beams were encapsulated in, and bearing on, the cellular concrete, while spanning over the tunnel, and transferring the load of the backfill above the tunnel away from it.
The Solution
CJGeo proposed a CJFill-UL as a value improvement over the organic foaming agent cellular concrete that was specified. The architect and structural engineer approved the proposed change.
CJGeo mobilized a four person crew and a 200CY/hour mobile batch plant, and completed the steam tunnel lightweight backfill work in three pours over two days. The CJFill-UL was generated using a synthetic foaming agent. It can be placed up to 20 thick at a time, and is generated onsite directly from bulk cement, so isn’t dependent on ready mix plant locations.
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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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8′ CMP Joint Grouting
The Job
A spec warehouse was planned for a vacant piece of land which had 1700LF of 8′ CMP running through it. The pipe was 10 years old. Because the site was vacant, there was no maintenance. Nearly every joint showed signs of soil infiltration, and there were massive sinkholes along the entire alignment. Given the depth, size, and short work window, the contractor sought out a CMP joint grouting repair alternative to replacement.
The Challenge
To avoid replacing the entire run of pipe, the joints had to be sealed. There were 80 pipe joints and 12 pipe to structure joints to seal. The pipe crossed under a roadway, and then crossed the site at an angle. The downstream end of the pipe transitioned to new 96″ RCP.
The Solution
In preparation for the repair, CJGeo had to educate the town, contractor, owner & consulting engineers that polyurethane grouting is an effective CMP repair method.
CJGeo mobilized a polyurethane grouting crew to the the site. Over the course of a week onsite, the crew performed all of the CMP joint grouting.
CJGeo used CJGrout 20SDB geotechnical polyurethane. 20SDB is a high mobility geotechnical polyurethane, so seeks out and fills even the smallest of voids outside of pipes. Because it’s highly mobile, it doesn’t deflect or damage the CMP that needs repair.
The manholes also had significant defects. Made of non-parged sewer brick, they leaked extensively. To address the widespread infiltration through the structures, CJGeo sprayed the interior of each structure with CJGrout 60FDC. 60FDC is a hybrid polyurethane/polyurea spray coating. For durability, the 60FDC was coated with polyurea. The 20SDB, 60SDB & polyurea coating were all installed using the same equipment, significantly reducing costs.
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Norfolk polyurethane grouting
The Job
This Norfolk polyurethane grouting project is located on a military base. The medical clinic on a military base was being renovated. As part of the renovation, the 650sqft elevated slab front porch needed to be replaced. The slab “sounded hollow,” and the presumption was that there were nominal voids below the slab.
The Challenge
At the start of demolition, the demolition contractor determined that the voids below the slab were closer to 3′ deep. This presented a safety problem for the demolition. The concern was that the slab would fail catastrophically during demolition. The general contractor reached out to CJGeo about ways to reduce the void depth.
The Solution
CJGeo proposed void filling below the slab using CJGrout 20SDB. CJGrout 20SDB is a low exotherm bulk void filling geotechnical polyurethane specifically formulated for deep fill placements without scorching or charring.
CJGrout 20SDB cures to 95% of final strength within a few minutes. Because of this, by the time the crew is packed up to leave the site, the material is effectively completely cured. This is significantly faster than cementitious grouts like flowable fill, and facilitates fast return to service. Because 20SDB is very light, it also reduces the likelihood of inducing settlement compared to traditional flowable fill.
A two person polyurethane grouting crew mobilized to the site and placed approximately 2,900lbs of CJGrout 20SDB in a few hours onsite, allowing the demolition contractor to safely resume work.
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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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Warehouse Floor Joint Stabilization
The Job
This floor joint stabilization project is located in Ashland, Virginia. About two months after occupying a new warehouse, the tenant identified two joints where the floor “popped” at a joint when a forklift drove over them. After consulting the plans, the owner determined that the joint wasn’t doweled, and needed warehouse floor joint stabilization.
The Challenge
Both affected joints were on main, high frequency travel pathways within the warehouse. So, any repairs had to be done quickly, and with zero impact to operations.
The Solution
CJGeo proposed undersealing the two joints, which had experienced slab curl, with high density geotechnical polyurethane grout. In fewer than three hours onsite, CJGeo undersealed the joints with CJGrout 20SDB, load tested them, and demobilized. There were no impacts to operations of the facility during this warehouse floor joint stabilization repair.
Undersealing is the best method for addressing slab curl joint popping. Grinding or polishing, an alternative method does not stop the movement. Filling joints with rigid joint filler can temporarily stop movement, but typically results in fatigue and cracking. Undersealing for slab foundation repair completely fills the voids below the floor so that the floor can’t move. If the curl is significant enough that it affects ride, polishing can be done afterwards to address ridges.
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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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