The Job
This TBM intervention permeation grouting project is located in Virginia. It is part of a highway tunnel installation project to increase capacity on a bridge tunnel.
The Challenge
During mining, the TBM, which is more than 40′ in diameter, began to pull pieces of sheet pile & wire rope through the face. To prevent further damage to the machine, tunneling was stopped. The machine encountered the debris approximately 250 feet short of the exit structure, underneath a constructed island.
The island is built out of relatively loose beach sand that’s commonly available in the area. The crown of the machine is approximately 25′ below grade, with the invert of the machine being about 70 feet below grade. Mean high tide is also about 25′ below grade.
In order to facilitate a hyperbaric intervention, the contractor needed a solid plug in front of and around the machine face. The criteria for the plug included:
- easily excavatable, to prevent issues for the TBM upon resumption of mining, and also to ensure that divers doing the hyperbaric intervention wouldn’t have issues removing grouted material in the case of grout entry into the machine face.
- low viscosity, to ensure uniform permeation into the soils in front of the machine, though they were relatively course (only 1% fines)
- readily available, in order to meet the incredibly short schedule requirement
The Solution
CJGeo proposed permeation grouting to create the plug using acrylic grout. Acrylic grout is:
- readily available through the mining supply chain
- very low viscosity, so well suited for permeating sands
- forms a stiff gel that’s stable, but still easily hand-excavatable
To perform permeation grouting up to 75 feet below grade, CJGeo proposed sonic drilling to install Tube-a-Manchette (TAM) pipes.
Due to the compressed timeframe, CJGeo subcontracted a sonic driller to install 86 different TAM wells, ranging from 25 to 75 feet deep. Once the first 10 TAM tubes were in place, CJGeo started placing acrylic grout through up to 10 simultaneous TAM pipes, using straddle packers and a PLC-controlled grouting system.
CJGeo was onsite within 10 days of the first call. Then, over 23 calendar days, CJGeo successfully installed more than 85,000 gallons of acrylic grout, at rates of nearly 15 gallons per minute.
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