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Launch Shaft Permeation Grouting

Fort Myers, Florida

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The Job

As part of a utility installation project, a 60″ MTBM was being launched from a shaft sunk in the middle of a nest of buried utilities, adjacent to an arterial roadway. Utilities included water, sewer, ITS, traffic signals, and others. The MTBM launch elevation was approximately 18′ below ground water.

The Challenge

The shaft installation contractor and adjacent open cut utility installations had experienced flowing sands, which had proven problematic. The tunneling contractor knew that without increasing the stability of the soils adjacent to 60″ hole they needed to cut in the sheet pile shaft walls, there would likely be significant loss of ground into the shaft, potentially damaging the adjacent utilities and roadway.

Soils excavated from the shaft were primarily fine sands, silty sands, and silt. Previous attempts at grouting the same soils with a prepolymer chemical grout had proven unsuccessful.

The Solution

CJGeo determined that acrylic grout would be the most appropriate to bind the soils together in order to make them stand vertically during cutting of the launch hold in the sheet pile wall.

Because acrylic grouts have single digit viscosities, they are able to permeate very find grained soils with ease, ensuring uniform stabilization.

CJGeo performed permeation grouting via holes cut in the sheet piling, and treated an approximately 8CY mass of soil. In addition to grouting the soils immediately adjacent to the launch hole, CJGeo performed leak stop grouting on numerous nuisance leaks throughout the joints of the sheet pile shaft.