The Job
This remote annular grouting project takes place near Roanoke, Virginia, for a trenchless crossing of the Appalachian Trail as part of an energy transmission project. The grouting location lies approximately 3 miles from the nearest road crossing, with slopes reaching up to 30%.
The project uses a 42″ steel product pipe within a 56″ tunnel through competent rock. Pipeline installation crews removed the tunnel’s casing for corrosion protection. Theoretical grout consumption for the 620 foot tunnel was 178 cubic yards.
The Challenge of Remote Annular Grouting
Initial planning for this crossing was to leave the casing in place with an ungrouted annulus. However, the decision to remove the casing, and therefore need to grout the annulus, was made a few weeks before final testing and gas on. This presented multiple challenges:
- Due to the remote location, the crew had to bring the grout in dry and mix it on site.. Any onsite ‘expansion’ would be beneficial to reduce the amount of material to haul to the placement location
- There was no opportunity to install sacrificial lines into the annulus, so all grouting had to be done in a single lift.
The Solution
CJGeo worked with the microtunneling and general contractors to design a grouting program that eliminated transportation and logistics risks and allowed for a single placement.
Working with the microtunneling and general contractors, CJGeo designed a grouting program and mobilized the necessary equipment, including two bulk cement tankers, a dry batch cellular grout plant, and a support truck.. The pipeline contractor then dragged all equipment to the placement location over two days and flew CJGeo’s crew in by helicopter. After completing all prep work, the crew successfully placed all the grout in approximately 1.5 hours. Uniform 30lb/cuft CJFill-Ultralightweight cellular grout venting from a 12 o’clock port on the far bulkhead confirmed the successful, complete fill.
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