Cellular Concrete Tunnel Abandonment

Challenge:

In the early 1990s, a deep foundation pile was driven through a sanitary sewer line and floor drain pipe under the basement floor of a hospital.  At the time, nobody knew that the pipes were there, or had been compromised.

During a renovation of the basement area to expand the adjacent radiation treatment center, the sewer line was video inspected.  The camera ran into the pile.  In order to repair the pipe and route it around the column, two access pits were dug, and an 80′ tunnel was hand excavated to expose the break in the pipes.  New pipes were installed, and routed around the offending pile.

When the repair was finished, there was a 230 cubic yard tunnel to fill.

Limits:

Given the sensitive nature of the work area, there were multiple limits to meet on this cellular concrete tunnel abandonment job.

  • The tunnel ran under a radiation treatment room, so due to the potential for radiological exposure, all work had to be completed off-hours.
  • Time was tight; the tunnel access pits were in rooms under renovation for installation of additional radiological treatment machines.
  • There was a total of 230’ pumping distance, 100’ of which was inside, 20’ below grade.  
  • The designer wanted to minimize the weight applied to the pipes by the tunnel abandonment material
  • The material needed to be excavatable.

Solution:

Cellular concrete tunnel abandonment in Washington, DCLightweight cellular concrete was chosen for the void filling because it is easily pumped, is self-leveling and very light weight.  Cellular concrete is very flowable and doesn’t segregate.  This allows it to be pumped long distances and still be uniform at placement and during curing.  This isn’t always possible with flowable fill, which is also significantly heavier than cellular concrete.

Cellular concrete is self-leveling to within a few inches per hundred feet.  This allowed for filling the tunnel from a single placement location, which minimized the disruption to other trades.

Result:

CJGeo successfully placed 230 cubic yards of material in two lifts.  Once the cellular concrete tunnel abandonment was completed, the floor access holes were patched, the renovation activity resumed.