Due to an oversight during construction, acidic groundwater at a coal mine in West Virginia was causing deterioration of 7′, 9′ and 10′ CMP bypass pipes adjacent to a coal stockpile. The pipes had been installed to bypass streams below the surface elements of the mine, but high iron content and low acidity of water entering the pipes caused the mine to have to treat the water which was supposed to be bypassed.
The pH of the water affecting the metal pipes was as low as 2.1. While typical chemical grouts have excellent histories resisting chemical attack at low pHs, low pH can affect the initial reaction. The owner and geotechnical consultant were also concerned about leak stopping work on the pipe causing water to flow outside of the pipe downstream to other areas which were yet unaffected.
CJGeo worked with multiple potential grout suppliers to identify a grout which would not be affected by the acidic environment. A 120cps high expansion prepolymer was chosen due to its ability to react properly in low pH environments, and also for its low viscosity to help ensure good coverage.
A CJGeo chemical grouting crew completed leak stopping on 31 joints and 25 point leaks throughout 600LF of pipe over a period of two weeks, in addition to grouting a 1200CF cutoff wall to stop water migration outside of the structure.
The asphalt parking lot over a 300′ run of 54″ RCP culvert kept collapsing. The public works department of locality determined that the joints between the 4′ sticks of pipe had not been properly gasketed or seated during installation. The pipe saw continuous flow of a small stream, entering at an end wall and discharging into a box culvert which crossed a public street. The drop inlet at the downstream junction between the RCP culvert and box culvert also had a failed 18″ RCP culvert feeding it, which had to be repaired multiple times using open trench excavation.
The municipality was looking for an affordable, proven, and non-disruptive solution. Replacement would have required removal of a structure, and prevented adjacent businesses from using their parking lot during the work. Relining was not practical due to multiple sewer and water utility lines crossing through the pipe. Significant joint offsets would have also made lining difficult.
Extensive voids were identified around the pipe through an inspection. Much of the water flow from the stream was passing under/outside of the pipe, causing the erosion and collapse of the overhead parking lot, and the floor of a storage building built over the pipe. Previous attempts at sealing the joints and filling voids around the pipe with concrete had failed.
Polyurethane grouting to fill voids around the pipe and seal the joints between the individual pieces of pipe, end wall and drop inlet. And, chemical grouting to treat a curtain at the upstream end to reduce subsurface flow, and at the downhill end to stabilize a joint in the failed small diameter RCP culvert entering the drop inlet.
CJGeo polyurethane grouting crews placed 50 cubic yards of NCFI high density, hydroinsensitive polyurethane and 45 gallons of polyurethane resin chemical grout for an upstream grout curtain over a period of three days to complete the repair. The repairs were all completed without disruption to the adjacent businesses or streets.
A 6′ deep sinkhole opened up adjacent to a stormwater manhole structure. The manhole was in an easement between two single family homes, and maintained by a municipality. Two misaligned joints were visible from the manhole, and were the cause of the sinkhole.
The two misaligned joints were under up to 8′ of cover. The repair had to seal the two misaligned joints and fill the extensive voids around the pipe that resulted from years of erosion.
Chemical grouting to seal the joints in the pipe. An internal form was used to minimize entry of chemical grout into the pipe.
CJGeo large diameter pipe repair crew installed chemical grout to seal the two misaligned joints and fill voids. The repair was completed in less than two hours, with no service disruptions.
Two underground stormwater sand filters at an apartment community wouldn’t hold water. The structures, which were assembled from 10′ diameter metal pipes needed to pass a water loss test before the property could come off bond. Previous repairs attempted included installation of internal joint rings and seals, which did not stop enough flow to pass the water loss tests.
The proposed repair had to accommodate multiple layers of previous repairs. The joints included four different materials–aluminized metal, galvanized metal, neoprene, and polyethylene. The structures were bedded in washed #57 stone, and were connected to the stormwater drainage system, so subject to live flow.
Sprayed high density polyurethane/polyurea hybrid to seal the joints internally. In addition, chemical grouting for joints which had been repaired previously using internal bands and polyethylene seals. The chemical grouting repair was designed to minimize loss of chemical grout into the surrounding stone beds. The previously-installed internal seals and bands were left in place and encapsulated in the joint sealant.
CJGeo large diameter pipe repair crew installed chemical grout to seal the leaking joints. Immediately after the sealing was performed, the structures were tested by the municipality. Neither structure leaked any water after CJGeo sealed the joints.
A sinkhole opened up in a drainage easement maintained by an HOA. The cause of the sinkhole was identified as an improperly-seated gasketed joint between two 24″ HDPE stormwater pipes. The sinkhole was large enough that a few minutes of digging with a shovel exposed the entire joint.
Chemical grout injection into the joint from the outside of the pipe to grout the annulus between the ID of the female and and OD of the male end of the joint.
Single component chemical grout injection successfully sealed the entire circumference of the joint. Visual inspection via injection holes was used to confirm complete travel of chemical grout around entire area of joint.
A sinkhole opened up in a drainage easement maintained by an HOA. The cause of the sinkhole was identified as an improperly-seated gasketed joint between two 36″ HDPE stormwater pipes. The pipes were approximately 5 feet below the surface, where there was a 3′ diameter sinkhole. The pipe had been poorly installed, so it suffered extensive ovaling due to compression of the top during compaction without lateral support.
Chemical grout injectioninto the sinkhole from the surface to fill the sinkhole and seal the pipe joint.
The stormwater pond in a neighborhood was not holding water. Geotechnical investigations of the lining material showed that it was adequate. The developer determined that outlet structure grouting may be required to address water loss around the buried structures.
Due to a very tight site, the pond was designed to release water through two structures feeding manifolds. While the pond was equipped with a well and pump to make up for water loss, the pond would still not stay at level. The inlet and two outlet structures were identified as potential flow paths for water exiting the pond, causing the level to drop.
The township engineer told the developer that if they could not get the pond to hold water, they were going to have to install a liner system, which was very expensive.
The repair had to be done without impacting water quality, well operations, or create large disruptions to the residents. Because the exact pathway of water flow around the structures could not be determined, the repair had to address water flows through various seepage paths around the structures.
CJGeo successfully performed chemical grouting to stop water migration through the stone beds on two outlet structures and an inlet structure. The work was completed in a day.
A large sinkhole opened up in the parking lot of a manufacturing facility. The sinkhole was adjacent to a cast-in-place stormwater drop inlet structure. The structure was 14VF deep, and was fed and discharged by 54″ HDPE pipes, requiring HDPE pipe joint sealing.
Facility maintenance personnel had been monitoring the sinkhole and noted that it was growing rapidly. Inspection of the pipe revealed that there were joint failures at the first joint out from the manhole, and deterioration of the parging. The parging between the HDPE and concrete pipe had failed to the point of significant amounts of soil washing out during rain events.
The repair had to be done without disrupting traffic in the parking lot. It also had to provide a long term solution to the failed pipe joints.
Along with gently filling the voids around the HDPE pipe without deflecting or damaging it, the repair material had to have enough expansive force to thoroughly seal the small cracks and leaks in the parging between the HDPE pipe and concrete structure walls.
Chemical grouting was chosen for injection through the joints of the HDPE pipe. Prepolymer chemical grouting uses single component polyurethane grouts with exceptionally long gel times. This virtually eliminates localized expansive pressure, which could further damage the HDPE pipe, which was already out of round.
Plural component structural foam was used for void filling the large sinkhole that extended from the bottom of the structure to the surface.
Prepolymer chemical grout was injected through the joints in the HDPE pipe. This successfully sealed the bell and spigot joints without causing further deflection of the pipes.
The large sinkhole void was grouting using plural component polyurethane grouting. A low exotherm structural foam was chosen due to the very large size of the void. Structural foams are important in situations where there are very large voids in areas subject to traffic loading.
Dam outfall pipe seep grouting, Fairfax, Virginia
A 36″ RCP outfall pipe for a dam terminated at an end wall. As part of a dam rehabilitation, small seeping leaks at the end wall/pipe joint needed to be stopped. The leaks had to be stopped so the wall could be resurfaced.
The engineer specified chemical grouting.
Access to the area was quite difficult. It was more than 150 feet from the closest vehicle access, which was only accessible by 4×4 vehicle down a steep slope.
While unknown during the planning of the chemical grouting repair, what was thought to be 36″ RCP was actually larger diameter RCP that had been lined with steel casing pipe. An interior poured-in-place concrete liner had been installed afterwards.
Super low viscosity prepolymer chemical grout was selected. This was for two reasons: 1) the ability to easily pump more than 150LF from the lay-down area. and 2) the ability to seek out and stop leaks through very tight cracks in the structures.
Prepolymer chemical grouts are water-reactive, so can be injected into active water flows. The grout expands when it comes into contact with the water, which seals of the leak.
The initial grouting plan was to install the chemical grout through the pipe wall starting beyond the first joint in. However, because the pipe had been cased, placement had to be done through the end-wall structure only. Multiple injection holes were drilled through the end wall structure, and the chemical grout was pumped through the end-wall structure.
Extensive catalyzation was used to first seal the leaks at the end wall and then chase the water flow pathways up along the outside of the pipe. The job was messy due to the forced proximity of the injection points and the leaks. But all the leaks were successfully stopped.
The roof of a rails to trails tunnel started to collapse. In the worst area, a 150 cubic yard cavity opened up at the tunnel crown. Previous rock bolting slowed, but did not stop the collapse. Due to the unsafe conditions, the tunnel was closed. Trail users had to use a 1.5 mile bypass to go around the tunnel.
GeoBuild & Gannett Fleming teamed up for the design build repair of the tunnel. After choosing a structural steel plate lining system for the repair, they turned to CJGeo to provide a back grouting solution. The tunnel is approximately 850 feet long, and 30′ in diameter, with an annular volume of approximately 2300 cubic yards.
It’s believed that the original tunnel was unlined, with bare rock surfaces. Over time, various lining materials were placed, starting with timbers. Some time after the timber lining was placed, concrete lining was installed. The concrete lining was up to 2′ thick in places. A contributing factor to the deterioration of the concrete liner was water accumulating in the timber lining, freezing and expanding behind the concrete lining.
The daylighting of an adjacent live railroad tunnel also posed challenges for the safety of the pedestrian tunnel. The haul road for disposal of the daylighting spoils passed over the top of the pedestrian tunnel. Approximately 1.5 million cubic yards of spoil were hauled over the roof of the pedestrian tunnel.
The biggest limit on this tunnel back grouting job was access. The tunnel was located 2 miles from the nearest paved road, down a single lane bike path. Once at the site, a 20 ton weight limit bridge stood between the staging area and tunnel. This effectively ruled out using low slump grout as the grouting material. Altneratively, low slump grout would have to be pumped 300 feet over the weight limited bridge to the portal and then another 850 feet through the tunnel. This is an exceptionally long distance to pump very low slump grout safely. Low slump grout is the typical grout recommended by the SSP liner manufacturer, Armtec. Minimizing cost was also important; the customer was a non-profit trail maintenance organization.
Cellular concrete was also considered as an option. Cellular concrete is primarily comprised of atmospheric air by volume. This would cut down by 80% the number of trucks needed to deliver grout to the site. However, cellular concrete is also exceptionally flowable. This posed problems in that the SSP plates are not designed to have water-tight joints. Given the tunnel size, there were nearly 20,000 linear feet of joint which would have to be water tight in order to use cellular concrete. Another limit of cellular concrete on this project was the very high potential for fouling the drainage system.
While contemplating using polyurethane grouting to seal the joints in the SSP liner to facilitate cellular concrete grouting, we thought “why not grout the whole thing with polyurethane.” For this project, polyurethane grouting offered a number of key benefits:
- Logistics; the entire 2300 cubic yard annulus would only require three truck loads of material delivered to the site. This alleviated concerns about bridge capacity & truck traffic on the bike path.
- Speed; CJGeo’s in-house polyurethane grout placement capacity exceeds 100 cubic yards per hour. This allowed the job to be completed in a timely fashion.
- Fast cure; the selected polyurethane grout completed expansion & cured within three minutes. This alleviated concerns about leaks through the joints in the SSP. It also allowed for deep, successive lifts.
- Strength; the selected material had a bearing capacity of 3700PSF, despite only weighing 2PCF.
- Cost; while the raw material cost was higher for polyurethane grout than cellular concrete, the savings from speed, insensitivity to joint leaks & logistics made polyurethane grouting the economical choice.
CJGeo placed 120,000 pounds of polyurethane grout in two weeks to complete the tunnel back grouting. In addition to the annulus, approximately 250 cubic yards were placed in the roof collapse cavities. Polyurethane grout was also used for bulk heading the ends of the annulus. CJGeo’s use of polyurethane grout was an unquestionable success.
Because the chosen polyurethane grout only weighs 2 pounds per cubic foot, it wasn’t necessary to perfectly balance injection across sides. This facilitated continued traffic through the tunnel for other activities associated with the relining.
Infrared inspection was used to confirm complete fill, in conjunction with visual inspection of joints & extrusion of polyurethane grout through vent holes.