The Job
This Massachusetts cellular grouting project is located in Cambridge. It is part of a new commercial construction project. SECA Underground microtunneled under the MBTA Red Line tunnel with a 200 foot long, 63" diameter steel casing. Once the casing was in place, they installed four, 18" diameter forcemain pipes and two, 4" diameter pipes in the casing. To ensure long term stability, the design engineer called for the tunnel annulus to be completely grouted.
The launch shaft, after carrier pipe installation.
The Challenge
Managing carrier pipe buoyancy on multi-carrier tunnels can be really tricky. This tunnel had six different carrier pipes, and 3 different spring line elevations. Therefore, using heavy grout in multiple lifts would have been practically impossible. Even if the math all checked out for multiple lifts of heavy grout, with the number of spacers, it would have been very difficult to keep the grout at a uniform elevation in the tunnel without a ton of sacrificial grout pipes.
The Solution
The retrieval shaft.
To solve the carrier pipe buoyancy problem, and design effectively all grouting pressure out of the placement, CJGeo proposed 30lb/cuft CJFill-Ultra Lightweight cellular grout. The grout provides sufficient compressive strength, and at half the density of water, designed all buoyancy concerns out by simply filling the carrier pipes with water.
Using cellular grout on this project took what would be a very risky and time consuming flowable fill grouting adventure and turned it into an effectively risk-free, two hour cellular grout placement.
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