Penstock Void Grouting
The Job
This penstock void grouting project is located near Hopkinton, New Hampshire. It is located at a small hydroelectric power plant that has been in service for more than 40 years.
The Challenge
This hydro-electric plant’s two original parallel penstocks are wooden. Sometime after original construction, 6.5′ ID steel liners were installed inside the original wooden penstocks.
Typically, when pipes are slip lined, the annular space between the ID of the original pipe and OD of the liner is grouted. However, in this case, the annulus was left open.
The steel pipes are nearing the end of their service life, and require rehabilitation. Plans called for installing a shotcrete liner. Specs called for a cementitious grout with 30 minute working time placement behind the steel pipes prior to spraying shotcrete.
The Solution
The marine contractor performing the shotcrete lining reached out to CJGeo about performing the annular space grouting with cementitious grout. CJGeo’s engineering & operations teams evaluated the project documents and site conditions and determined that there was a very high risk of grout escaping the annulus and making it to the adjacent waterway. This was due to the unknown condition of the original wood penstock, minimal cover over the pipes, and unknown, but potentially open graded backfill material.
CJGeo proposed an alternative, using CJGrout 22SHV geotechnical polyurethane grout to perform the penstock void grouting. CJGeo’s alternative material proposal was accompanied by load calculations from our geotechnical professional engineer confirming that despite strength significantly less than the specification requirement, that CJGrout 22SHV provided multiple factors of safety beyond the actual loads the annulus would see.
Upon approval by the owner’s consulting engineering team, CJGeo mobilized a confined space polyurethane grouting crew to the site. Over two days, the crew successfully grouted the annular space between the steel and wood penstocks. The following day, the contractor began installing reinforcement and prepping the steel pipe surface for shotcrete application.
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Ohio Polyurethane Grouting
The Job
This Ohio polyurethane grouting project by CJGeo was for a short line railroad near Scio, Ohio. The railroad received numerous complaints from motorists about a settled grade crossing. The settlement of the precast grade crossing was great enough to also require a speed restriction for rail traffic.
The Challenge
When this precast grade crossing settled, the clips holding the rail to the crossing panels broke. This allowed significant differential settlement between the various panels. The differential settlement was up to two inches.
In order to install new clips, the panels generally have to be within 3/8-inches of the adjacent panels’ elevation. If any debris has accumulated between the rail foot and bearing surface of the precast panels, which in this case were Oldcastle’s StarTrack.
The Solution
Having repaired multiple precast crossings for this short line, they reached out to CJGeo about performing this Ohio polyurethane grouting project. CJGeo proposed CJGrout 40NHL geotechnical polyurethane grout to the railroad. CJGrout 40NHL is formulated for high dynamic loading environments, and is excellent for different settlement correction of thick pavements.
CJGeo mobilized a polyurethane grouting crew to the site. Due to relatively low traffic on the line, the customer was able to provide an eight hour window for the repair, and the DOT allowed a complete road closure, as the settlement affected both lanes, with the centerline being the worst spot on the crossing.
CJGeo crews used mechanical assistance to address some of the worst differential settlement. Cleaning the accumulated debris between the rail foot and panels was key to facilitating complete correction of the differential settlement. After CJGeo wrapped up the polyurethane grouting, the railroad’s maintenance-of-way crew installed new clips, replaced the boots, and patch the adjacent asphalt.
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Flooded Shaft Grouting
The Job
This flooded shaft grouting project by CJGeo is located outside of Washington, DC at a data center site. As the 60″ microtunneling machine was entering the retrieval shaft, a piece broke off of the secant pile wall, and tore the seal. This resulted in water infiltration of around 600 gallons per minute into the shaft. The machine was recovered, but the shaft filled with nearly 15 feet of water in a matter of hours.
The casing crown has roughly 20 feet of cover, and is about 15 feet below the ground water level. The ground in the area is a mix of clays and sands. The tunnel is primarily in the underlying fractured rock. For the last 30 feet of tunnel before the secant pile receiving shaft, the tunnel is in a mix of weathered rock and sandy clay.
The Challenge
Having used CJGeo in the past to address high volume leaks into shafts, the tunneling contractor reached out to CJGeo for this flood shaft grouting problem. The primary constraints were:
- time – the project was already behind schedule
- water management – any groundwater was considered contaminated
Typically, grouting a leak such as this would be as simple as throwing bigger pumps into the shaft, dewatering it, then grouting the leak from inside the shaft. However, because of the costs associated with treating potentially very high volumes of water at this site, this wasn’t an option.
The Solution
CJGeo proposed, and then successfully performed, a two stage grouting program. Primary grouting was done using CJGrout 35NHV61 geotechnical polyurethane on a Saturday. The CJGrout 35NHV61 was installed immediately behind the secant pile wall through three holes drilled from the surface to intercept the over cut. Grout injection through these holes resulted in grout return to the retrieval shaft. Off gassing also showed up at the launch shaft. This indicates that the rapid inflow of water during the flooding event had washed out some of the mud in the over cut.
After completion of the plural component primary seal injection, CJGeo dye tested the primary grouting program. This was done through Tube-A-Manchette grout pipes installed using sonic drilling along the tunnel alignment, further out from the shaft. No dyed water returned to either shaft.
The following day (Sunday), CJGeo performed permeation grouting using colloidal silica through the TAM grouting tubes. This secondary grouting program served two purposes:
- seal any rock fractures that weren’t penetrable by the higher viscosity plural component polyurethane grout
- replace any overcut mud washed out during the initial flooding event
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RCP Joint Sealing
The Job
This RCP joint sealing project is located near Charlottesville, Virginia. The polyurethane grouting work was subcontracted to CJGeo as part of an on call contract for stormwater structure and dam maintenance with a municipality.
The Challenge
Pavement distress of an asphalt roadway over a small dam prompted an inspection of the triple barrel 48 inch RCP structure passing through the dam. Upon inspection, significantly less water was flowing through the pipes than was flowing through the downstream spillway.
On each of the three pipes, water was flowing out of the endwall around the RCP inverts. There was relatively little cover on the pipes. This would make open cut replacement relatively simple. However, the roadway is the primary access to a neighborhood. Thus, a trenchless grouting repair to address the joint failures and piping was optimal.
The Solution
CJGeo worked with the on-call contractor, and owner’s dam engineering consultant to design a grouting program that not only addressed the piping and joint leaks, but also the voids in the fill material between the pipes and roadway.
Over the course of two days onsite, a CJGeo polyurethane grouting crew grouted each of the three pipes using CJGrout 35NHV61 geotechnical polyurethane. 35NHV61 is provides adequate bearing capacity for typical roadway loading, performs identically in flowing water and dry environments, and is certified for potable water contact.
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North Carolina Annular Grouting
The Job
This North Carolina annular grouting project is located in Havelock, North Carolina. Havelock is home to Marine Corps Air Station Cherry Point. US 70 passes through Havelock, providing a critical link between New Bern and the coastal beaches of North Carolina.
The Challenge
As part of North Carolina DOT work to upgrade the capacity and increase safety of US 70, a number of wet utilities were upgraded and relocated. This required a number of jack and bore crossings of the existing roadway to avoid disrupting traffic. NCDOT requires annular grouting for jack and bore crossings of wet utilities, for anything with less than a 100 year design life.
The Solution
This project had two crossings needing annular space grouting. One was 120 linear feet of 42″ steel casing with an 18″ ductile iron pipe water line. The second was 86 linear feet of 42″ steel casing with an 18″ ductile iron water line.
A CJGeo cellular grouting crew successfully filled each of the two casings with CJFill-Ultra Lightweight cellular concrete in a few hours in a single day. Carrier pipe buoyancy was not a concern due the low density of the grout.
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Bridge Approach Grouting
The Job
This bridge approach grouting project is located near Lexington, Virginia. It is on Interstate 81, which has some of the highest truck traffic in Virginia. The Virginia Department of Transportation maintains this section of Interstate 81.
The Challenge
Settlement over time caused voids under three lanes of approach slab at an overpass structure. During precipitation events, the voids became saturated, and then act as diaphragm pumps. The high dynamic loads from the heavy truck traffic effectively pump the fines out of the saturated base materail.
Over time, this resulted in extensive deterioration of the adjacent asphalt pavement, along with distress of the concrete approach slabs.
The Solution
Working with the local bridge maintenance group and their on-call maintenance contractor, CJGeo proposed a polyurethane bridge approach grouting program to restore stability to the slabs. Previous repair attempts had used flowable fill to attempt to fill the voids below the pavement. This generally doesn’t work very well, and proved to not be suitable in this case, either.
Primarily constrained by maintenance of traffic concerns, CJGeo undersealed all three lanes of the approach over two nights. Grouting was done using CJGrout 40NHL, which is optimized for heavy loads, wet environments, and is capable of lifting settled pavements.
Because 40NHL cures to 95% within a few minutes, by the time the injection holes are patched, treated slabs and soils are ready for traffic as usual.
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Electric Bore Annular Space Grouting
The Job
This electric bore annular space grouting project is located in Norfolk, Virginia. As part of significant work at the Port of Virginia’s Norfolk International Terminal, an electrical contractor installed seven jack & bore crossings of various roadways and railroad lines within the port.
The Challenge
There are seven bores, ranging from 85 feet to 362 feet. Each bore is 36″ steel casing, with eight, eight inch conduits. Most conduits are for electrical lines, some are reserve, and some are for communication and data.
The designer’s specification call for annular grouting of all the conduits, with a minimum 1000psi grout. There was no thermal conductivity requirement.
The Solution
CJGeo proposed a 60lb/cuft CJFill-Standard cellular grout in order to meet the 1000psi requirement. Buoyancy control was achieved through water filling of the conduits, along with a conduit & casing spacer design which presumed some buoyancy.
The customer filled each of the conduits with water prior to grouting. Due to the relatively low volume of grout per bore (ranging between 16 & 57 cubic yards), CJGeo used a local ready mix supplier for paste, and the wet batch generation method. CJGeo successfully performed the electric bore annular space grouting work over two days.
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Railroad Bore Annular Space Grouting
The Job
This railroad bore annular space grouting project is located in Winchester, Virginia. As part of a new development, three parallel stormwater pipes were bored under a CSX right of way.
The Challenge
The railroad requirements include annular space grouting. The three casings (80 feet long each), are 48″ by 0.725 wall thickness steel. The carrier pipes are 30″ N-12 pipe, with a 35.50″ outside diameter.
This annulus requires about 16 cubic yards of grout per bore. One of the challenges of double wall HDPE drainage pipe is that it is exceptionally light. This can make uplift management during grouting particularly challenging.
The Solution
In order to manage buoyancy during the annular grouting, the boring contractor installed longitudinal blocking on each of the carrier pipes during installation. To reduce the uplift by six times compared to flowable fill, CJGeo proposed a 30lb/cuft cellular grout for the annular grouting.
Between the blocking and the very low density CJFill-Ultra Lightweight cellular grout, single lift grouting was possible without damaging the new carrier pipes. Single lift grouting eliminates the risk of trapped air pockets or partial fills associated with multi-lift grouting.
Due to the relatively low volume, and to reduce heat of hydration, wet batch generation using slurry from a local ready mix plant was used. Cellular concrete is also referred to as low density cementitious material.
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Tunnel Adit Fill
The Job
This tunnel adit fill project is part of the Purple Line project outside of Washington, DC. Specifically, the adit is located at the pedestrian connection between the Purple Line project and WMATA’s Bethesda station on the Red Line.
The Challenge
Plans call to connect the Purple Line to the Red Line using an adit constructed during the original construction of the Red Line. The adit is approximately 30 feet wide by a 35 foot tall arch. During preparation to blast from a shaft dropped adjacent to the station, a fault was identified passing through the adit.
The construction and design teams were concerned about stability of the adit during blasting operations as the Purple Line access tunnel was excavated towards it. The team determined that filling the adit to plug and stabilize it during blasting would be the most risk appropriate move.
Filling the adit would fulfill the design challenge of stabilizing the rock during blasting. However, it created the following challenges:
- the tunnel adit fill material would need to be removed after blasting was completed
- the adit is approximately 100 feet below grade
- there is very limited space up top
- material couldn’t segregate, and had to be pumped approximately 250 feet in addition to the 100 foot drop
The Solution
The tunnel engineer of record recommended CJGeo to the contractor. The EOR is familiar with CJGeo’s cellular concrete generation and placement expertise, and thought that cellular concrete would be the lowest risk way to fill the adit, while facilitating excavation and removal afterwards.
CJGeo took five days onsite to fill the adit, in lifts up to eight vertical feet. Due to the potential dead load from the rock cover, 400psi CJFill-Standard was the material of choice. By using our colloidal mixing dry batch process, the material set off quickly, ensuring that it would not consolidate during cure as lower energy mixing methods can suffer from.
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New Jersey permeation grouting
The Job
This New Jersey permeation grouting project is located in Elizabeth, New Jersey. It is at a large wastewater treatment plant owned by the JMEUC.
The Challenge
During installation of a new building on site, a large excavation was required. Primarily comprised of H piles and wood lagging, it crossed a 24 foot wide influent conduit. The influent conduit is a double barrel box structure, cast in place on 12 inch thick bed of open graded stone.
During test pitting to the bottom of footing elevation, the test pit appeared to be tidally influenced. The site is immediately adjacent to a creek that feeds into the Elizabeth River. At high tide, and due to the permeability of the stone layer, inflow into the test pit was not controllable, and was higher than the footing elevation.
Specific challenges here included:
- potentially high velocity water flows due to tidal influence
- 12 foot minimum spacing of grout holes due to structure wall locations
- potential fouling of bedding stone with fines
The Solution
The general contractor reached out to CJGeo about grouting the stone bed. The structure is 24 feet wide, but only has a single, eight inch wall down the middle.
CJGeo proposed that a coring contractor drill a two inch core down through the center and side walls from the surface. This gave us three access points to place grout from at each location.
Due to the large grout hole spacing, CJGeo selected acrylic grout. Acrylics are excellent for this type of application because they are exceptionally low viscosity (pump & flow pretty much like water).
A single CJGeo chemical grouting crew performed the acrylic grouting over two days onsite. Afterwards, infiltration into the excavation was down to a submersible garden hose pump. The use of acrylic grout ensured that:
- coverage was uniform despite the large distance between placement points
- any fines fouling the bedding stone were uniformly bound together, immobilized & made impermeable
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