Tampa Microtunnel

Tampa, FL


As part of a large design-build utility rehabilitation and capacity improvement project, a 60″ micro tunnel was dug under an interstate. The tunnel was approximately 40 feet below grade, and 1050LF. Due to the length of the tunnel, traditional grouts were unlikely to be successfully placed for the annular space grouting. Concerns with traditional grouts included flowability, carrier pipe buoyancy, and high pumping pressures, compounded by a local shortage of flash, which was a critical component of the planned grout.

The tunneling contractor reached out to CJGeo to see if cellular concrete would be a feasible product for the annular space grouting. The project was located near Tampa, Florida.



CJGeo proposed cellular grout to avoid the challenges associated with fine aggregate based grouts. To meet the 1,000psi requirement at 28 days, CJGeo proposed a 60lb/cuft CJFill-Standard, generated using Aerlite preformed foam, and continuous generation.  

Cellular concrete provided a few key benefits for this project:

  • material supply–cellular concrete does not require fly ash in order to be highly mobile and pumpable
  • low unit weight–by being less dense than water, cellular concrete does not cause the water-filled carrier to be buoyant
  • flowability–cellular concrete is very highly mobile
  • economics–the 400CY project volume would take two days


CJGeo mobilized a cellular concrete crew to the site. Using continuous generation and slurry from a local ready-mix supplier, CJGeo grouted the annulus completely. Completeness of fill was verified by uniform material venting from each of the vent and placement pipes at both ends of the tunnel.

Peak pumping pressure during grouting was approximately 8psi when grouted through the annulus.

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