Trenchless Repair of a Broken Sewer
The storm-water drain that starts from the street near the Mattox’s driveway, runs between our houses next to the Mattox’s path, and ends up in the ravine, has been broken for many years. Twice Fulton County said they had repaired it but in fact all they did was replace washed-away soil. Eventually enough soil had washed away that a sinkhole appeared in Dan & Leigh Ayn’s yard and we noticed our terraces had begun to collapse. We are now part of Alpharetta City – no longer part of Fulton County, so Dan called the folk at the City Municipality and, after someone came out and looked at things, they said they would fix it. Things seemed to stagnate but then two-or-so weeks ago huge trucks parked outside and their crews washed and cleaned out the drain.
This morning a convoy of trucks converged on the road outside. Amongst these was a refrigerator truck, an air-compressor, and a truck containing a steam generator. The steam-generator truck pulled into the Mattox’s driveway and they set to work.
The refrigerator truck contained a resin-saturated felt tube. The chilling was necessary to delay any curing of the resin until the tube had been laid. The workers cut a hole into the side of this tube toward the beginning and attached a coupling to which a hose from the compressor could be attached. This end of the tube was then folded inside-out back over the tube and mounted in a small jig. With the resin providing lubrication and a clamp on the rig making a seal, as high-pressure air was introduced the tube was pulled from the refrigerator truck and down the sewer pipe.
Eventually the other end of the tube appeared. I had expected it to be sealed but while it was closed there was room for air to escape. As one of the workers explained to me the tube was now half-way down the sewer and they would use the high-pressure air to force the second half through the first, but the end was open as they did not want the tube to expand right then – just move down.
Finally the tube reached the manhole at the bottom end of the sewer and was guided upwards by ropes and finally popped out and was blowing in the wind.
At this stage both ends were clamped hard shut and more compressed air was forced into the tube to expand it against the walls of the sewer. Excess resin would be forced into any cracks in the sewer walls. The action of forcing the tube against the walls of the sewer was why the sewer had to be washed out and cleaned first.
The steam generator was now coupled into the compressed-air hose and hot steam was fed down the tube to cure the resin. The steam was allowed to escape through a valve at the far end of the tube. Once the resin had cured the tube was as firm and rigid as a PVC pipe and the excess lengths at the start and end of the tube were cut off and discarded.