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.
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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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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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Precast Lagging Wall Lateral Load Reduction
The Job
This load reduction backfill work as associated with the replacement of Scaife Hall, at Carnegie Mellon University, in Pittsburgh, Pennsylvania.
The Challenge
The H-pile and precast lagging wall is at the top of a steep slope. There is a Class I railroad line at the base. Because of site constraints, an HDPE stormwater detention structure is within the fill area. Along with extensive stormwater pipes and manholes.
In order to optimize the drilled shafts for the H-piles by reducing the lateral loads, the designer sought a lightweight, permeable backfill material that would not apply lateral loads once in place.
The Solution
CJGeo proposed 20lb/cuft CJFill-High Permeability cellular concrete. CJFill-HP would minimize lateral loading on the wall during construction, buoyancy of of the stormwater system components, and ensure a free draining material.
Because the material is permeable (modified ASTM D-2434 2.0cm/sec), it is freely draining and reduces hydrostatic loads on adjacent structures.
620 cubic yards of lightweight backfill were placed over two mobilizations to complete this load reduction backfill project.
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250000 Gallon Oil Tank Abandonment
The Job
This oil tank abandonment project is located in the nation’s capitol, Washington, DC. As part of decommissioning an underground oil tank at Howard University in Washington, DC, it needed to be filled with excavatable material that was lighter than the roughly 55lb/cuft heating oil it was designed to hold.
The tank is under a small empty lot. The lot is up for redevelopment in approximately three years.
The Challenge
For a complete decomissioning, the tank had to be completely full of grout. Since it sits within a planned basement excavation, the fill material has to be easily excavatable.
The Solution
CJGeo proposed 20lb/cuft cellular concrete for the oil tank abandonment grouting. This afforded plenty of factors of safety to reduce the likelihood of settlement induced by filling the tank and maximized excavatability. The removability modulus of 20lb/cuft (a quantifiable method for determining excavatability of various types of flowable fill) is much less than one. This means it is easily hand excavatable.
CJGeo placed the CJFill-Ultra Lightweight fill material over a period of two days onsite. Because cellular grout is highly mobile, no entry was required during the placement of the fill material, which designed a significant amount of risk out of the process.
The 1200CY placement was performed over two days onsite.
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Fire Station Floor Lifting
The Job
This fire station floor lifting project is located about an hour east of Richmond, Virginia. The concrete slab on the grade floor inside of a fire station on the North Neck of Virginia settled up to two inches. As part of the investigation into the cause, an engineer discovered voids up to 8″ below the slab and multiple broken sanitary sewer pipes below the floor.
The affected areas needing slab foundation repair included a dayroom, kitchen & meeting hall.
The Challenge
In order to minimize disruption to the fire station’s operations, the proposed repair had to be quick, clean, and minimize uncertainty associated with the plumbing repair slab cuts.
The Solution
CJGeo performed ground improvement grouting of the underlying soils to 5′ below-grade utilizing plural component polyurethane compaction grouting, with CJGrout 35NHV. During the compaction grouting process (sometimes called structural polymer grouting), the CJGrout 35NHV lifted the floor back into place.
Because polyurethane grouts cure very quickly, the floor was repaired the day before the plumbing work was scheduled. This allowed the plumbers a stable work surface and eliminated the risk of stuck saws or sudden collapse of the floor during floor sawing for plumbing access.
Grouting sufficiency was verified by using pre & post-grouting DCP tests.
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Multiplate Tunnel Grouting
The Job
This multiplate tunnel grouting project is located in Asheville, North Carolina. During a real estate transaction, civil engineers walked a 1400LF run of 14′ diameter multiplate tunnel running underneath a strip center and multiple outparcels.
A previous inspection had indicated impending section loss of the pipe due to corrosion and had recommended grouting of incidental voids, but no work had been performed at that time.
The pipe, which had up to 20′ of cover, bypasses a large stream and runs under 200LF of building footprint, the main entrance roadway, two out-parcels, and ties into an NCDOT box culvert to discharge.
The Challenge
Significant debris was present in the pipe, and access was exceptionally difficult. Because dewatering was not practical, all work proposed had to be performed underflow.
The Solution
CJGeo proposed polyurethane backgrouting using plural component CJGrout material, specifically CJGrout 35NHV61.
CJGrout 35NHV61 is a hydro insensitive, moderate mobility grout. It’s designed for backgrouting in wet environments, and is certified for potable water contact.
Despite a bear wandering into the pipe during repairs, CJGeo crews successfully backgrouted the pipe to address piping and erosion outside of the structure over a period of two weeks. More than 40,000 pounds of CJGrout 35NHV61 were needed for this 14′ CMP repair project.
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Corporate HQ Stabilization
The Job
Starting immediately after construction was completed, the slab on the grade floor within the cafeteria, loading dock, and kitchen at a corporate headquarters building in Pittsburgh, Pennsylvania settled. Over the course of 12 years, the owner had four different grouting companies attempt to address the problem. Lime slurry injection below the slab was disruptive, and settlement always resumed shortly thereafter.
Compaction grouting was performed in one area but was so disruptive that despite the fact that it was the only method where settlement didn’t resume, the owner kicked the contractor off the site after nearly four months of not having access to their executive dining room.
The Challenge
Settlement progressed over time to be as much as four inches, affecting nearly 20,000 square feet of floor. A general contractor retained by the owner reached out to CJGeo about performing low-impact grouting to address the settlement.
Because settlement affected the entire kitchen, food prep, serving and majority of the dining areas, repairs had to be facilitated continued use of the facility. Additionally, due to the 24-hour staffing of the facility, the noise had to be limited, and there was zero tolerance for dust.
Video inspection of the extensive gravity sanitary and floor drains below the floor revealed six defects, including a 2″ offset in a sanitary drain line for a 6 stall restroom.
The Solution
CJGeo performed 17 DCP tests to determine the depth of uncontrolled fill, which was the presumed cause of settlement. DCP testing showed pockets of WOH fill down to 35′ below the finish floor, and voids ranging from 2″ to 18″ immediately below the floor.
Over the course of 7 nights onsite, CJGeo crews installed 12,000 pounds of CJGrout 20SDB into voids immediately below the floor, and 53,000 pounds of CJGrout 35NHV61 for polyurethane compaction grouting. Compaction grouting was performed up to 35′ deep, but to an average depth of 15′ over the entire area.
All work was completed off-hours. As soon as the kitchen shut down for the evening, CJGeo crews swung into action, grouting through the night until wrapping up in time for the food prep crews to get ready for breakfast at 0500.
To facilitate grouting under four walk-in freezers and refrigerators, over the course of a 24-hour shift, all cold contents were moved to reefer trailers, CJGeo grouted to 30′ under the freezers and refrigerators, which were then immediately turned back on, and then refilled.
Through careful coordination with multiple operational divisions for the owner, general contractor, flooring restoration contractors, plumbers, and remediation contractors, CJGeo successfully completed the project under budget and on time.
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Sewer Collapse Sinkhole Repair
The Job
This sewer collapse sinkhole repair project is located in central Virginia. When the operators of a tire and auto shop noticed a sinkhole developing next to their building. They weren’t sure what to do. After an employee crawled into the hole and discovered that he could stand up underneath their building, the owner reached out to the city. City crews determined that a 20″ VCP combined sewer & storm pipe had collapsed under the structure, roughly 25′ below grade.
The Challenge
An on-call contractor for the city installed a new manhole and rerouted the pipe around the building. However, addressing the sinkhole was out of their businesses’ scope. The project manager reached out to CJGeo, who visited the site and recommended DCP testing to better quantify the extent of the problem.
The Solution
DCP testing showed that outside of the large hole on the surface, there was little deep disturbance. Working with the city’s consulting engineer, CJGeo developed a grouting plan to install two different CJGrouts. 20SDB in the bulk voids near the surface. And 35NHV61 for soil grouting to address voids within the underlying ground near the failed sewer line.
While onsite for just 6 hours, a CJGeo crew completed the work with zero disruption to the businesses’ operations.
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School Floor Leveling
The Job
This school floor leveling project is located in Princeton, West Virginia. The Princeton Middle School is a slab-on-grade masonry structure and serves approximately 550 students in grades 6 through 8.
The Challenge
The corridor floor in the arts wing settled up to 3.5 inches. A geotechnical investigation found voids up to 2.5 inches below the settled slab. Due to budgetary constraints, the repair needed to address the settlement & instability without requiring flooring replacement.
A hand auger confirmed that the fill material below the slab had consolidated to the point of providing sufficient capacity. So, there was no need for polyurethane compaction grouting, which would have been useful if the soils were still loose.
The Solution
CJGeo mobilized a two-person polyurethane grouting crew to the site. Over a few hours, they filled all the voids utilizing CJGrout geotechnical polyurethanes and corrected the settlement. After the floor was lifted back into position and the voids all filled, the custodian reinstalled the cove base at the correct height. CJGeo patched the injection holes with off-white stained grout to match the VCT flooring.
CJGeo used CJGrout 28FDL for this repair. 28FDL is a fast, dry environment lifting foam that works great for lifting bellies out of lightly loaded slabs. There were no water leaks below the slab, there was a significant belly, and the loads were less than one tenth of the grout’s capacity, so it was a great fit. To make sure there weren’t any remaining voids, the crew installed CJGrout 20SDB, which is higher mobility than 28FDL.
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