25 metres of solid concrete drilled out of deep drain

Remote cutting system avoids renewal of residential drain

Brandwells, a UK regional groundworks contractor, started work on a new residential development on a brownfield site. Some of the existing foul drain connections on the site had not been capped and concrete from the new foundations found its way into the main 225mm clay drainpipe in the street and set, causing several major obstructions. Originally contracted to clear a single known blockage, Tube Tech successfully cleared the drain run of three concrete obstructions using a specially-designed and configured system, without any damage to the clay pipe.

When the site was cleared not all entry points to the existing foul drains had been recorded and sealed.
As the contractor began pouring concrete for house foundations other properties in the road started experiencing problems with their drains.
The drains were investigated with an inspection camera to ascertain the nature and extent of the problem and a large amount of concrete was found.
Initially only one obstruction was located - 17 metres long and 84 metres from the access point.
Tube Tech were originally contracted to clear this one obstruction but three partial or complete obstructions of set concrete, measuring 17, 8 and 4 metres in length were eventually discovered in the 225mm i/d drain.

Of the two manholes in the drain run only one offered suitable access for a large pressure hose to be introduced into the drain and be able to move freely.
In addition it was preferable for the operators if they could work on the surface rather than 3 metres below ground which would require them to wear breathing apparatus and safety harnesses.
Even so, the contractor had to reduce the access hole to make this possible.
From the modified access hole, it was 84 metres in one direction to the first obstruction and 70 metres in the other direction to the second.
A specialised system was devised and assembled at Tube Tech's head office and the mobilised to site.
A series of roller guides at the manhole ensured that the large pressure hose fed into the drain without snagging and helped reduce operator fatigue.
Thanks to careful matching of the low-pressure, high-volume system with the right pump, all the concrete was removed without damaging the clay drain pipe; in fact it was not even scratched.
There was supposed to be no aggregate in the concrete obstructions but the largest piece removed measured 1.5 metres in length and was full of aggregate, which increased the challenge for the removal head.

Scott Donson, Technical Sales Manager: “The Brandwells team were delighted – they had been faced with the prospect of replacing 200 metres of foul drain and re-housing the occupants of the 50-60 properties connected to it while the work was carried out. Replacement would have also required the permission of the water authority, which was likely to be difficult to obtain. All in all, this job was just the kind of challenge we relish and our reputation for solving such problems is growing all the time.”