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.
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.
Power Station Pipe Abandonment
The Job
Dominion’s Bremo Bluff Power Station was taken off line in 2019. As part of complete decommissioning, demolition was performed in 2022.
The Challenge
Four, 48″ cooling water pipes needed to be filled with grout to ensure longterm stability of the surrounding area. In addition to the pipes, a junction box they all connected to needed to be filled.
The Solution
CJGeo generated and placed approximately 300CY of 50psi cellular concrete to fill the junction box and pipes. The material was generated onsite over the course of a few hours using dry batch generation.
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.
Hotel Basement Water Intrusion Grouting
The Job
A hotel in Baltimore had a continuously wet floor in the basement utility room. Water was oozing out from under the power feed bank housekeeping slab, which had been poured on top of the floor slab. There were two presumed point sources: the unsealed joint between the floor and the wall, and the power feed conduit wall penetrations. The pit where the power conduits came through the wall and turned up into the power feed cabinets was 18″ deep, and always full of water.
The Challenge
Extensive exterior drainage work had been done under the presumption that surface water was flowing down the outside face of the basement wall, and then through the unsealed floor:wall joint and/or into unsealed joints in the conduits and then through the conduit penetrations. The exterior drainage improvements, which included re waterproofing approximately 500sqft of wall, slowed, but did not completely stop the water intrusion.
A forensic engineer overseeing the project reached out to CJGeo about performing chemical grouting inside of the utility room to underseal the floor, and to seal the conduit penetrations.
The Solution
CJGeo proposed chemical grouting utilizing a low viscosity hydrophobic prepolymer chemical grout.
Fibrous material soaked in grout was placed into the utility conduit openings to seal them against water intrusion. The 250sqft floor was then undersealed with grout, which extruded up through the joint between the wall and floor, and also through various cracks in the floor.
Upon completion of the grouting by CJGeo, the conduit pit was dry, and there are no longer any leaks.
Dollar Store Floor Void Filling
The Job
A commercial contractor was performing a full gut renovation of a dollar store in a strip center. The building was approximately 30 years ago, and there were no signs of floor slab failure or settlement.
The Challenge
While cutting through the floor to install utilities, a 3″ void was discovered below the floor. Exploratory coring determined that voids ranged from 0.5 to 4″ throughout approximately 11,000 square feet of the space.
The Solution
CJGeo mobilized two geotechnical polyurethane grouting crews to the site and filled the voids over a period of two days. Approximately 7,000 pounds of CJGrout 20SDB were placed through approximately 500, 5/8″ holes, with cross-hole communication cutoff criteria. The work was performed without disruption to the renovation activities.
25MGD Sinkhole Leak Grouting
The Job
An underground minerals mine started to lose up to 8VF per day of mine due to water infiltration. Investigation of an adjacent stream uncovered multiple sinkholes which had opened up where the stream crossed a fault. Two sinkholes were adjacent to bridge abutments of a public road, which served as the sole access for multiple homes and farms.
The Challenge
Mine personnel started to self-perform chemical grout in some of the sinkholes. Due to the slow rate of grout installation relative to the water flow, the self-performed grouting was unsuccessful.
Due to endangered fish habitats within the stream, cementitious grouts weren’t allowed, and any chemical grouts needed to be certified for potable water use.
The Solution
CJGeo mobilized two polyurethane grouting crews in the third week of the Covid-19 pandemic to the site. To facilitate safe access to the site, all grouting was performed from aerial platforms reaching out over the work area.
During the grouting process, multiple additional sinkholes opened up; CJGeo would seal one sinkhole, and an adjacent soil filled feature would blow out. Super sacs of aggregate were dropped in the sinkhole throats to fill the bulk of voids, and then polyurethane grouting was performed below the super sacs.
Using nearly 50,000 pounds of CJGrout 35NHV61, CJGeo was able to slow the leaks to the point where no additional sinkholes formed, and the mine’s pumps were able to dewater the facility.
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.
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.
