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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Coke Gas Pipe Fill
The Job
This coke gas pipe fill project is located in Middletown, Ohio, at Cleveland Cliff’s Middletown Works facility. Middletown Works determined that the coke plant would be more costly to repair than to replace, so elected to demolish the plant.
The Challenge
A demolition contractor working to dismantle parts of the onsite coking plant had to remove approximately 350LF of coke gas pipe. The work area is located in the basement of the coking plant.
Coke gas residuals will spontaneously combust when exposed to the air, but the pipe had to be cut into roughly 3′ pieces to remove it. The pipe fill grout had to:
- completely fill the pipe
- coat the residuals to minimize air exposure
- cut easily
- add as little weight as possible to the pipe sections
The Solution
CJGeo proposed using CJGrout-20SDB to fill the pipes. 20SDB is a 2lb/cuft rigid polyurethane foam, specifically formulated to flow long distances before setting.
CJGrout 20SDB is generated onsite by special polyurethane grouting rigs. The rigs have hoses up to 400 feet long, which convey the material from the grouting rigs to the placement area. For this coke gas pipe fill project, the crew had to run hoses approximately 250 feet into the building, down multiple stair cases. The hoses are lightweight and about 2 inches in diameter, so this isn’t a problem.
One of CJGeo’s polyurethane grouting crews was onsite for two days to complete the project. Once the coke gas pipes were filled, the demolition contractor cut them into 3 foot long pieces with traditional band saws bagged the sections, and removed them from site.
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Lightweight Temporary Dam Foundation
The Job
This lightweight temporary dam foundation installation was part of flood proofing project a nuclear power plant. The temporary dam can be quickly installed between two large structures in the case of anticipated storm surge. This is to keep flood waters from inundating a sensitive area.
The Challenge
The cooling water pipes for a reactor pass under where the dam goes in the case of a predicted flood. If placed, the dam exceeds the design load of the underlying cooling pipes.
The Solution
The designer elected to excavate 3′ of fill from above the pipes and replace it with 25lb/cuft CJFill-UL . Removing 3′ of 120lb/cuft material and replacing it with 3′ of 25lb/cuft, reduces dead load by roughly 275lb/sqft. The 25lb/cuft material can float, however. So, to address buoyancy, given the minimal cover (2″ of asphalt), geogrid cast into surrounding high density flowable fill acts as a hold down.
CJGeo poured the lightweight temporary dam foundation in two lifts. To void being in a cold joint, the geogrid was placed on sewer bricks. This ensures at least 6″ of embedment in the top layer of CJFill. To assess the readiness of the CJFill-Ultra Lightweight for paving, CJGeo cast a test slab for the customer to run heavy equipment over prior to loading the production area.
This was the first project where CJGeo utilized geogrid for buoyancy control of cellular concrete.
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Industrial Basement Abandonment
The Job
This industrial basement abandonment project is located in Southside, Virginia. As part of an adaptive reuse project of an abandoned industrial site, the former onsite power plant’s stacks were being rehabilitated. Multiple tunnels and basement rooms had to be completely filled.
The Challenge
Due to safety concerns, nobody could enter the basement. No as-builts were available. Camera inspection through holes cored in the ceiling showed significant numbers of passageways and obstructions. The fill material had to be:
- exceptionally mobile,
- placed in deep lifts,
- and as light as possible.
Fill density was a concern because the basement was up to 15′ deep. 150lb/cuft traditional flowable fill would have caused too much anticipated settlement. Settlement of the basement structure could potentially cause settlement or movement of the adjacent smoke stacks.
The Solution
CJGeo proposed 25lb/cuft cellular concrete for the lightweight fill material. Using onsite colloidal batching, CJGeo can place material up to 20′ deep in a single lift, without consolidation. Because CJFill-Ultra Lightweight is so lightweight, the entire 15′ deep basement fill dead load was the same as from just 2′ of traditional flowable fill. For this application, Aerlite-iX was the most appropriate cellular concrete foaming agent.
CJGeo mobilized a 150CY/hour dry batch plant to the site after staging 300 tons of cement onsite using our in-house cement pig & trucking operation. Over four days onsite, CJGeo place 2700CY of CJFill-Ultra Lightweight material to complete the industrial basement abandonment.
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Power Station Pipe Abandonment
The Job
This power station pipe abandonment project is between Richmond & Lynchburg, Virginia, along the James River. Dominion’s Bremo Bluff Power Station was taken off line in 2019. As part of complete decommissioning, demolition and site restoration took place in 2022.
The Challenge
Power stations typically have extensive pipes for cooling water circulation. At Bremo Bluff, the buried cooling pipe network consists for four, four foot diameter pipes, connecting to a junction box. Total linear footage of the forty-eight inch pipes is about six hundred linear feet.
Due to the remote location, the demolition contractor knew that it would be difficult to get timely deliveries of the nearly 40 loads of flowable fill needed to fill the pipes.
The Solution
The demolition contractor reached out to CJGeo for consultation on the best type of flowable fill for the pipe abandonment work. CJGeo recommended 25lb/cuft CJFill-Ultra Lightweight. 25lb/cuft CJFill-Ultra Lightweight has a 28 day compressive strength (ASTM C495) greater than 50 psi. This met the owner’s requirements.
25lb/cuft CJFill-Ultra Lightweight is nearly 80% air content. Therefore, each twenty-five ton load of cement delivered to the site turns into nearly 150 cubic yards of finished product. Due to this on-site expansion, instead of needing nearly 40 loads of ready mix flowable fill, the work only needed two loads of cement.
CJGeo generated and placed approximately 300CY of CJFill-Ultra Lightweight cellular concrete to fill the junction box and pipes. CJGeo made all of the material over a few hours onsite, using dry batch generation.
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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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NY Thruway HDD Annular Space Grouting
The Job
This HDD annular space grouting project is east of Buffalo, New York, under the New York Thruway. As part of distribution improvements, National Grid’s contractor bored 830LF through rock using HDD. The bore was 30″, with a 16″ HDPE casing, carrying three, 4″ HDPE conduits.
As part of the installation, the NY Thruway Authority call for casing back grouting, and the casing pipe’s annular space grout filling.
The Challenge
The proposed back-grout had to be:
- pumpable 830LF at very low pressure,
- dense enough to displace the 10 pound per gallon drilling mud, and
- provide sufficient strength to meet Thruway requirements.
The proposed annular space grout had to be:
- pumpable 830LF at very low pressure,
- light enough to not apply excessive pressure on the conduit pipes, and
- also provide sufficient strength to meet Thruway requirements.
The Solution
CJGeo proposed two different grout mixes to meet the project requirements. 85lb/cuft CJFill-Under Water casing backgrout for the displacement of the 10PPG (75lb/cuft) drilling mud. And 25lb/cuft CJFill-Ultra Lightweight annular space grout within the casing.
CJGeo’s crew mobilized to the site, and successfully performed the back-grouting and annular space grouting in a single day. A tremie pipe strapped to the HDD casing was used for the back grouting. By pumping the 85lb/cuft (11 pound per gallon) CJFill-Under Water to the low point, the drilling mud was floated out of the reamed hole annulus.
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Coal Pier Sinkhole Grouting
The Job
This pier sinkhole grouting project by CJGeo is located at the mouth of the Elizabeth River, off the Chesapeake Bay. With an annual throughput capacity of 48 million tons, Norfolk Southern’s Pier 6 at Lamberts Point in Norfolk, Virginia is one of the largest coal trans-loading facilities in the world. As an around-the-clock facility built around precision logistics, there’s little tolerance for disruption or downtime.
The Challenge
When two sinkholes opened up at the end of Pier 6 adjacent to the bulkhead, railroad personnel reached out to an onsite maintenance contractor. Steel plates were installed to provide temporary protection while a long-term solution could be implemented.
The Solution
CJGeo performed DCP testing at the site in order to quantify the depth of voids below the pavement adjacent to the sinkholes. The DCP testing showed that in addition to large voids visible from the sinkholes immediately below the pavement, there were large pockets of voids down to 15’ below the surface.
CJGeo crews then used CJGrout 35NHV61, a hydro insensitive, NSF-certified geotechnical polyurethane to fill all voids and restore stability to the area. The grouting work took five hours onsite to install 3400 pounds of material, with zero disruption to operations.
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Acid Drainage Grouting
The Job
This acid drainage grouting project is located in West Virginia. A 72″ CMP stream diversion pipe under a coal stockpile at a coal mine in West Virginia was experiencing acidic water infiltration. This was causing bypassed stream water to become acidic, so regulators required all of the stream flow to be pumped to treatment ponds and treated. This was expensive, and the flow volume was greater than the design capacity of the treatment system.
The Challenge
Access was quite challenging. The pipe was either 700LF or 1300LF from the nearest access points to the farthest grouting location. Additionally, the infiltrating water was pH 2.
Due to location, all personnel had to be MSHA 40 hour trained, and the company registered as a mine contractor with the state.
The Solution
CJGeo recommended a hydrophobic prepolymer chemical grout with an extensive performance history in high acidity environments. CJGeo crews sealed a combination of 20 joint leaks and point infiltration sources using the prepolymer chemical grout.
To address acidic water migrating through the stone dust backfill outside of the pipe, CJGeo crews then grouted an in-situ cutoff wall in the trench just downstream of the lowest leak using permeation grouting. Permeation grouting is optimal for creating small footprint cutoff walls because it typically doesn’t require large equipment. The mine operator installed two dewatering wells immediately upstream of the cutoff wall to intercept and pump out the acidic drainage, to keep it isolated from the stream water.
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Tub Crossing Repair
The Job
This tub crossing repair was done for a short line railroad in New Jersey. The sandy soils of South Jersey are great for growing produce and mining pure silica sand. While most of the produce is shipped by truck, a lot of the silica is shipped by rail. The rails inevitably cross the roads, and many of the crossings are at grade.
The Challenge
A short-line railroad was experiencing significant settlement and pumping of multiple precast modular crossings in the Vineland & Millville areas. Each crossing saw significant truck traffic, primarily from aggregate mining, and also significant heavy haul rail traffic from transporting sand.
Voids below the panels were holding water due to poor drainage. Each time a truck or train passed over the panels, they deflected downwards. This deflection pumps base material out from under the crossing, causing settlement.
The Solution
Working with a rail maintenance contractor, CJGeo performed polyurethane grouting on a total of four precast tub crossings in the area, using CJGrout 40NHL. Each crossing repair took a single day. Polyurethane grouting allowed for the immediate resumption of automobile traffic, and rail traffic. Th CJGeo crew installed supplemental bolting to address the deterioration of the panels resulting from the extensive movement of the panels.
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