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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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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Facing a similar challenge? Give us a shout or shoot us a text. Click the state marker for the location of your project for contact info for the appropriate rep.
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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Facing a similar challenge? Give us a shout or shoot us a text. Click the state marker for the location of your project for contact info for the appropriate rep.
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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Facing a similar challenge to this power station pipe abandonment project? Give us a shout or shoot us a text. Click the state marker for the location of your project for contact info for the appropriate rep.
