Annular Space Grouting–48″ Force Main

Annular Space Grouting–48″ Force Main

Challenge:

Annular space grouting in a swamp. Three stretches of pipe required annular space grouting:

  • 1500 linear feet of 48″ HDPE inside of a 60″ RCP jacket,
  • 100 linear feet of 48″ HDPE inside of 54″ steel casing from directional boring under a stream, and
  • 30 linear feet of 48″ HDPE inside of 54″ steel casing directional bored under an 18″ gas pipeline

The general project was installation of a new 48″ collector main feeding a regional sewage treatment plant.

Limits:

The HDPE pipe manufacturer specified that the grouting pressure had to be below 5psi.  Due to the layout of the site, the cellular concrete had to be pumped more than 300 feet to reach the run under the gas main, which still had to be grouted at fewer than 5psi.  

Solution:

Cellular concrete was specified by the project engineer due to low injection pressure and ability to be pumped long distances.  Cellular concrete was an ideal solution for the annular space for a few reasons:

  • High flow.  Cellular concrete is exceptionally flowable; it’s self-leveling to a few inches in 100 feet.  This allows for pumping long distances at very low pressures.
  • Low installation pressure.  Because cellular concrete is so flowable, high pumping pressures aren’t required.  This leads to a safer jobsite and a lower risk of affecting plastic pipes.

Result:

CJGeo placed the lightweight cellular concrete to fill the annular space to the engineer’s specification.  Truck batch cellular concrete generation was used due to the need to frequently move injection locations.  In order to meet the project’s 100psi compressive strength requirement, CJGeo placed 30PCF wet cast density mix, which has an average compressive strength of 150psi.

Pumping pressures never exceeded the 5psi specified limit.  The installation was completed over a few days without disruption to other construction activities on the site.