Tunnel Saved by Flyash

by Keith M. Swaffar, (M.ASCE), Proj. Engr.; Neyer, Tiseo and Hindo, Ltd., Detroit, MI,
Harry R. Price, (M.ASCE), Proj. Engr.; Neyer, Tiseo and Hindo, Ltd., Detroit, MI,

Serial Information: Civil Engineering—ASCE, 1987, Vol. 57, Issue 9, Pg. 68-70

Document Type: Feature article


When inspection early in 1986 showed that Detroit's Northeast Raw Water Tunnel was near collapse at one location, quick action and a unique use of flyash-cement grout or fill to temporarily support the tunnel from within prevented collapse. The flyash-cement-water material is 50% water by colume and only 5% cement. In 10-14 days it gained sufficient compressive strength (60-100 psi), when inserted at the subsidence location and between two bulkheads, to temporarily support the 10 ft interior diameter unreinforced concrete tube. Another unusual feature was the 10 ft diameter rubberized fabric bladders, filled with water, and used as the two bulkheads. The flyash cement grout was weak enough to be readily removed by clay spades when no longer needed.

Subject Headings: Fly ash | Tunnels | Hydration | Material failures | Grouting | Compressive strength | Coastal protection structures

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