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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Tunnel Abandonment – Boston
THE JOB
A plumbing contractor hand tunneled 140LF of 4’x5′ tunnel under two apartment buildings near Boston, Massachusetts. In preparation for a renovation project, a structural inspection was performed. The structural inspection revealed the slab floors which were tunneled under were not designed as structural slabs. The structural engineer directed the property owner to immediately fill the tunnels to restore structural integrity.
THE CHALLENGE
The tunnel abandonment work had to be completed during the winter, and while one of the two affected buildings was occupied. The non-occupied building was also in the process of asbestos abatement and a full gut renovation.
Due to the plumbing running through the tunnels, an excavatable grout was required. Also, the grout had to be low exotherm in order to not affect the new PVC plumbing.
THE SOLUTION
CJGeo proposed polyurethane grouting for the tunnel abandonment. Polyurethane grouting can be performed in any weather, is low exotherm, and can be placed in very thick lifts. The specific grout chosen was a low exotherm bulk void filling polyurethane.
CJGeo mobilized a polyurethane grouting truck with more than 9000 pounds of polyurethane grout, due to the unknown exact volume of the tunnels. During an 8″ snowstorm, CJGeo abandoned both tunnels in a single day. The unoccupied building was grouted via holes drilled through the floor. The tunnel below the occupied building was free sprayed from inside the tunnel. All tunnels were kept under negative pressure ventilation in order to address installation odors.
CJGeo placed 4100 pounds of polyurethane grout into the two tunnels.
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Office Floor Settlement Repair
The Job
This office floor settlement repair project is located near Norfolk, Virginia. The slab floor inside of a grain import/export facility office sank both differentially and globally. All exterior walls are on driven timber piles, but the floor floats independently of the foundations. Slab settlement up to 3 inches affected approximately half of the building footprint.
The Challenge
Over the roughly 15 years that the floor was settling, maintenance crews were constantly repairing various systems. These repairs were including tuckpointing CMU walls, moving/shimming HVAC ducting, and rerouting water lines.
The foundation repair work on this building couldn’t impact operations. Ship loading and unloading could not be disrupted for any reason. The settled building houses many operations critical to ensuring timely loading and unloading.
The Solution
CJGeo proposed polyurethane grouting for this slab foundation repair project. Polyurethane grouting is safe, fast, and economical for floor settlement repair. Structural polymer grouting is another name for polyurethane grouting. The material of choice was CJGrout 28FDL. 28FDL is optimal for lifting light duty commercial floors experiencing both global and differential settlement.
CJGeo mobilized two polyurethane grouting crews to the facility on a Saturday morning. The 4,000 square foot repair only took nine hours start to finish. There were zero disruption to operations. During lifting, previous cosmetic repairs were undone to facilitate lifting. This included removing extensive patch material from the CMU walls, loosening plumbing connections, and adjusting HVAC ductwork.
By mobilizing multiple crews with multiple equipment redundancies, CJGeo was able to ensure that the repair had zero disruptions to the facility and its operations.
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Port Shed Floor Stabilization
THE JOB
This port shed floor stabilization project is located in Baltimore, Maryland. The 11″ thick slab floor of a storage shed at a port facility settled up to 6 inches. Exploratory coring & non-destructive imaging (GPR & microgravity) indicated there were extensive voids below the floor.
Previous work on the adjacent bulkhead uncovered extensive voids below the exterior footings (pile-supported) and multiple abandoned, but unfilled, pipes under the floor.
THE CHALLENGE
Due to relatively thin voids, which were all less than 6 inches, and void filling grout had to be highly mobile. However, this posed environmental challenges due should the grout make its way into an unfilled abandoned pipe and into the adjacent waterway. The owner did not want to lift the floor, so grouting had to be sufficiently low mobility to prevent runaways, but also fill all voids at an economical hole spacing.
THE SOLUTION
CJGeo proposed polyurethane grouting for this slab foundation repair project. The original design was for a 50/50 mix of polyurethane and cement grouting. CJGeo proposed a valued engineering proposal to perform all grouting with polyurethane. CJGrout 35NHV geotechnical polyurethane grout was proposed to balance mobility for completeness of fill and reaction time to avoid any runaway loss into the adjacent waterway.
CJGeo mobilized a two-reactor polyurethane grouting rig and installed approximately 6300lbs of polyurethane grout over a three-day period. Pneumatic rock drills were used to speed drilling.
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Commercial Floor Void Fill
THE JOB
This commercial floor void fill project is located in Manhattan. During a Local Law 11 inspection, the owner of a coop building’s first floor asked the GC to investigate a settled slab floor inside part of the building. The contractor began opening up a 2′ square hole in the floor. During this, all the debris was disappearing. After opening the hole it was apparent why. There was a 2′ to 3′ deep void around the entire perimeter of the building footprint.
THE CHALLENGE
Filling a 90CY void under the floor of an operating business can be a challenge anywhere. Complicate it with a 40′ x 10′ laydown area, Mid-Town Manhattan traffic, and cold winter temperatures, and you’ve got quite the challenge.
The cause of settlement was the consolidation of poorly placed fill, which was primarily construction debris. Lightweight void filling material is best to minimize future settlement of the underlying fill material.
THE SOLUTION
At the suggestion of an on-staff structural engineer, the general contractor’s project manager reached out to CJGeo about performing polyurethane grouting to fill the voids. CJGeo proposed using a low-exotherm, high mobility bulk void filling foam to fill the voids. 3′ deep voids are too deep to fill with most polyurethane grouts. A true low exotherm foam is needed for efficiently and safely filling any voids thicker than about 6″. High mobility foams are also critical when filling voids in order to ensure complete coverage.
CJGeo mobilized a two-reactor polyurethane grouting rig. The CJGeo crew installed approximately 4800lbs of CJGrout 20SDB geotechnical polyurethane grout over a two-day period. CJGeo pulled continuous negative pressure on the void through the floor. This was to allow for continuous operation of the facility during grouting. CJGeo’s work didn’t disturb operations at all. All of the voids were completely full of grout at the end of the project. The polyurethane grouting process used here for slab foundation repair is sometimes also called slab jacking or structural polymer grouting.
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Warehouse Floor Water Intrusion Repair
The Job
This warehouse floor water intrusion repair project is located in Columbua, South Carolina. An area of the floor inside of a produce processing facility experienced water intrusion through joints in the floor. Considerable amounts of process water were dumped on the floor each day, and unsealed joints in the floor allowed water to collect under the floor slab.
The floor was showing signs of slab curl from poor control of the curing process after placement. With dynamic loading from material handling equipment, water was pumping through the joint onto the floor. Due to the slab curl, the floor was effectively acting as a diaphragm pump. The facility’s health & safety staff was concerned that the water could introduce contaminants to the food processing area.
The Challenge
The proposed repair had to perform well in saturated conditions, allow for near immediate resumption of material handler equipment, and ensure a long-term fix. Since no settlement had occurred, the grout material had to be able to seal the very small voids, displace water, and not exert any lifting forces on the floor.
The material & process also had to be perform well at cold temperatures–the facility is at 34 degrees year-round.
The Solution
CJGeo proposed chemical grouting using a hydrophilic prepolymer grout. Chemical grouting is ideal for saturated environments and helps to ensure complete stabilization and sealing of floors.
A single CJGeo chemical grouting crew mobilized to the site and performed the slab foundation repair work in a few hours. The water intrusion grouting work started after the second shift. The grout set to tolerate material handling equipment before the start of the first shift.
The following day, the facility reported no water extrusion under material handler traffic.
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Industrial Facility Floor Repair
THE JOB
The slab floor inside of a manufacturing facility in Hagerstown, Maryland settled. This caused equipment that was installed on the slab to become misaligned, requiring industrial facility floor repair.
A geotechnical investigation revealed voids below the slab due to the settlement of the underlying soil. The affected area was built over approximately 10 feet of fill during construction. Engineering analysis showed that the soil was likely poorly compacted, but had consolidated with time.
THE CHALLENGE
Due to the sensitive electronic equipment within the work area, the repair had to be very clean and dust-free. Though analysis determined that the underlying soils had most likely completed consolidating, the owner’s geotechnical consultant recommended limiting additional weight placed on the fill material.
The repair area was also more than 100 feet from the nearest exterior access. The floor had started to settle before the equipment was installed. It was very important that the slab not be lifted during the void filling process.
THE SOLUTION
Geotechnical polyurethane grouting to fill the voids below the slab floor. Polyurethane grouting is superior to mudjacking in situations like this because it is considerably cleaner, much faster, and allows for immediate reuse.
The material used in polyurethane grouting is much lower weight than mudjacking grout. This reduces the weight applied to the underlying soil. Lower weight materials reduce the chance of resettlement.
A single CJGeo polyurethane grouting crew completed the industrial facility floor repair in less than a day, using CJGrout 20SDB. Due to the extreme sensitivity of the equipment to lifting, a specially-formulated plural component polyurethane grout was selected for undersealing without lifting.
Precision equipment was used to monitor the floor during undersealing. A movement of 0.02 inches was used to determine the completeness of fill. This was confirmed by extensive extrusion of polyurethane through the adjacent saw cut control joints in the floor. Rotary lasers are the most appropriate for monitoring floor elevations during grouting operations. It’s important to ensure that the base station is well outside the zone of influence of grouting.
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Grain Bin Floor Repair
THE JOB
The floor of a 105′ diameter grain bin settled. The floor had a bin sweep installed, that was mounted on the top of the unloading tunnel, which ran down the center of the structure. Where the slab floor butted up to the tunnel walls, the floor had settled 2″ on one half, and 3.5″ on the other half. This caused issues with operating the bin sweep because it was designed for a smooth, level floor.
The owner’s alternative was to remove the entire floor and pour a new floor. This would have been incredibly expensive and taken a very long time. The only access into the bin was two 2′ wide by 4′ tall doors, located 5′ above exterior finish grade, and 2′ above the bin floor elevation.
THE CHALLENGE
Due to the nature of the commodity business, mobilization and completion of the grain bin floor repair had to be fast. Additionally, the repair had to return the floor to its original profile, along with the turned-down ventilation trenches in the floor. The extensive turned-down ventilation troughs made this floor very susceptible to cracking. The floor was 6″ thick but then went to 24″ thick at the ventilation troughs. Slabs with non-uniform thickness require extreme care and attention to avoid differential lifting.
The design loads for the floor are approximately 3500psf. So, the material used for lifting the floor had to be relatively high strength.
THE SOLUTION
CJGeo proposed polyurethane grouting for filling the voids below the floor and lifting them back into place. The minimum bearing capacity of the proposed materials was 5500PSF, ensuring adequate bearing capacity even under full load.
CJGeo mobilized two polyurethane grouting crews to the site. The concrete lifting work was completed over a period of two days. CJGeo placed more than 7,000 pounds of polyurethane grout using three reactors running simultaneously. CJGrout 28FDL is optimal for differential settlement correction, and thus the primary grout. Secondary grouting using CJGrout 20SDB is optimized for undersealing, so chased any nominal voids left by the relatively low mobility CJGrout 28FDL.
Multiple reactors (pumps) helped to ensure thorough lifting of the slab and the ventilation troughs. The crews that completed this job have collectively performed millions of pounds of polyurethane grouting, ensuring the successful completion of this grain bin floor repair job.
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Warehouse Floor Lifting
THE JOB
25,000 square feet of the industrial floor at a military facility settled up to 4 inches and was affected by sub-slab voids. This warehouse floor lifting project also included 250 track feet of embedded rail, which was set in an independent, thickened slab section. The building had been used for warehousing but was being transitioned to light manufacturing/maintenance.
There were extensive voids below the floor. The voids were located with GPR, and confirmed with cores. Because the floor had cracked extensively as it settled, the designer called for a 4″ un-bonded overlay after stabilization.
THE CHALLENGE
The proposed repair method had to provide adequate bearing capacity for manufacturing and ensure complete void filling and stabilization.
THE SOLUTION
CJGeo provided a value engineering proposal to use geotechnical polyurethane instead of cementitious grout. The VE proposal was based on the following:
- lower unit weight, so less likelihood of causing additional settlement
- adequate strength to ensure uniform load transfer to the underlying soils
- simplified logistics into a secure facility (all material delivered in just two truckloads)
The specified grout had an in-place density exceeding 115 pounds per cubic foot. The proposed polyurethane grout, CJGrout 40NDV, has a constrained density of 5.5PCF, yet a bearing capacity exceeding 12KSF.
CJGeo mobilized three polyurethane grouting crews to the facility, with a combined pumping capacity exceeding 5,000 pounds per hour. CJGeo crews injected the CJGrout 40NDV through nearly 2,000 dime-size holes drilled in the slab to complete this concrete lifting project.
The cutoff criteria for void filling was cross-hole communication or 0.1 inches of lift. The settled areas of floor raised an average of three inches. The embedded track area raised up to four inches.
It took CJGeo fewer than 10 days to complete this warehouse floor lifting job. Because the material cures to 95% within a few minutes, the overlay preparation crew worked a day behind the polyurethane grouting crews.
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