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Mass Lightweight Fill

By applying unique solutions to increase the safety and longevity of our environment.

Lightweight Plaza Fill

The Job

Lightweight plaza fill for a private age restricted high rise new build in Tysons Corner, Virginia.

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 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 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 was approximately 2200CY.

Hollow Abutment Filling

The Job

As part of a bridge rehabilitation for MassDOT, two hollow abutments needed to be filled in order to turn the structural approach/departure slabs into slab on grade.

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. In order to reduce the loads applied to the bridge from the backfill, the lightest possible material capable of providing sufficient support to the pavement was required.

Due to integrated beams for the structural slabs, there were 12 different individual pockets which were up to 2′ tall, which had to be vented independently during the final lift, 4 of which had to be under live traffic because the road couldn’t be completely closed.

The Solution

CJGeo worked with the general contractor to formulate a plan to vent the individual pockets from outside of the open lanes, to ensure a complete fill without requiring a complete road closure. Over the course of two mobilizations, CJGeo placed 2,840CY of 25lb/cuft cellular concrete to fill the abutments.

Grain Silo Tunnel Backfilling

The Job

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

To address the possibility of coastal flooding, the entire structure needed to be constructed above grade, including the 8′ tall unloading conveyor tunnels. The structure was designed to bear 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, which 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 cellular concrete to fill the silo bases up to flush with the top of the unloading tunnel walls. Rodbusters were able to start setting steel the day after completion of the final lift in each of the silos.

9.5kCY MSE wall backfill

The Job

As part of increasing the capacity of Interstate 95 north of Baltimore, Maryland, Express Toll Lanes are being added in the center of the existing roadway.

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 the interstate has widened, it’s gotten closer and closer to the PCCP water line. As part of this project, there are extensive ramp and embankment sections which are immediately adjacent to the waterline, which is not in a condition to see any increase in loading.

To address this, extensive use of lightweight backfill is required to increase elevations while not increasing loads on the fragile, and very critical, pipe.

The Solution

In order to facilitate construction of a roughly 850LF MSE wall running parallel to the waterline, lightweight backfill was required. Originally designed for backfilling with Lightweight Expanded Shale Aggregate (LESA), CJGeo worked with the contractor to develop a hybrid 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, which 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.

Utility Tunnel Abandonment

The Job

As part of a commercial building renovation, approximately 750CY of subbasement and utility tunnel needed to be filled.

The Challenge

The structural engineer had two concerns: the slab over the basements needed to be replaced, but couldn’t be removed until the walls were braced, and 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 cellular concrete, with an average of 80psi compressive strength for backfilling the tunnel and subbasement. Because 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 material saved approximately 1ksf in dead load relative to conventional fill materials, and provided sufficient strength to brace the walls to facilitate floor removal, and also provide adequate bearing capacity for the new floor.

Lightweight Tank Foundation

The Job

During an industrial facility expansion, a new blending tank needed to be 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. extending a few feet out around the perimeter of the tank foundation.

The Solution

After the concrete foundation contractor excavated the pit, CJGeo mobilized to the site and placed 110CY of 25lb/cuft cellular concrete into the pit. The placement took less than an hour, and the foundation contractor was able to start setting steel and forms the following morning.

30k CY Lightweight Embankment

The Job

As part of the redevelopment of the Sparrows Point industrial area of Baltimore, three bridges needed to be replaced.

The Challenge

When the bridges were originally constructed, the embankments were built with industrial byproducts over underlying compressible soils. As part of the reconstruction, the embankments needed to be widened and raised up to five 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 induce differential settlement.

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 LESA or FGA, didn’t require onsite stockpiling, and freed up the general contractor’s labor force to perform work other than placing aggregate.

Sloped Pit Lightweight Backfill

The Job

This work was associated with 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. However, given the uneven soil slope, this would have been very challenging to install.

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.

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 .9psi.

Rail Bridge Pier Stabilization

The Job

This project was a capital repair to a bridge pier for a Class I railroad serving 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, bearing on a timber pile supported timber mat. 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, and 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, and 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 material. The second, smaller diameter, ring of steel was installed, and CJGeo then filled the annular space between it and the necked down pier with 45lb/cuft material.

The cellular concrete was installed over a period of four days onsite.

Stem Wall Backfilling With Cellular Concrete

The Job

This work was associated with the construction of a new academic building at a school in Lynchburg, Virginia.

The Challenge

Due to a sloped site, 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, 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

CJGeo proposed installing 23lb/cuft cellular concrete to speed up the installation, reduce supply chain risks, and reduce the loads applied to the foundations and underlying soil.

CJGeo placed 1914CY of cellular concrete over three days onsite. All material was walkable within 12 hours, and the project saved approximately 3 weeks relative to the original design’s timeframe.

The cellular concrete was brought all the way to the bottom of the 6″ stone layer below the slab, and the plumbers were then able to excavate through the cellular concrete with a mini excavator and hand tools to install the plumbing, and the trenches were backfilled with 57 stone.

The total load using cellular concrete was reduced by approximately 120lbs/sqft relative to the EPS/stone dust backfill design.

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