Contractor PBF Drainage was initially tasked with carrying out a CCTV survey for a client due to sewage showing at ground level on a treatment works.
On completion of the survey, it was discovered that the short section running under a concrete chamber housing multiple electrical cables and some additional pipework was in urgent need of repair.
The client excavated on the first initial location which was approximately 6 m in length and 4 m in depth. Initial inspection showed the pipe obvert had completely disintegrated. The pipe walls were about 10 mm thick from around the 9 o’clock to 3 o’clock positions. The CCTV survey showed that the pipe obvert in the unexcavated section was also at serious risk of collapse due to missing sections.
Due to the severity of the condition of the pipe, a fast reliable and strong repair was required. PBF Drainage was tasked with finding this solution. Excavation was not an option as the use of Vac-Ex equipment, could not reach over the initial excavation safely and the use of any sort of heavy equipment meant that the pipe beneath would be likely to collapse.
Measurements taken of the pipe and inconsistencies in size and shape meant the contractor needed to offer a solution that would be suitable.
Along the pipe length, the diameter varied from DN450 to DN375 which was the original size and the size of the upstream section which was of Vitrified Clay pipe construction.
After speaking with its supplier, Terry Ingleby of S1E in Barnsley, PBF Drainage found that Quick-Lock, a localised repair system, suited the project requirements.
Quick-Lock is an entirely mechanical, seamless assembly system for localised repairs inside pipes ranging from DN 150 to DN 800 (and over 2 m on request) in any common wastewater, well or drinking water pipe system.
Quick-Lock units are a specially manufactured stainless-steel shell and EPDM rubber seal. The stainless-steel shell has a special locking mechanism which is located in a corresponding slot that has teeth cut into it, which acts as a ratchet. The shell is placed over a high-pressure inflatable bladder that runs on wheels. This bladder is pushed or pulled into place along with the Quick-Lock unit, monitored by CCTV equipment. Once in place, the bladder is inflated between 3 and 5 bar locking the shell into place, sandwiching the EPDM seal between the stainless shell and the pipe wall. The Quick-Lock units are available in a range of sizes from DN100 to DN2000 with different installation methods being used for the Quick-Lock Mini and the Quick-Lock Large products.
It was decided on this occasion that a series of Quick-Lock units would be installed, each within a pre-liner to prevent any over expansion due to the size changes within the pipe. This also meant that PBF Drainage could marry the repair up to the upstream section of pipework which had been replaced at an earlier time.
During the cleaning process a small section of subsoil fell into the pipe. This back fill contained stone, rubble and other hard objects which caused issues with the pre-cleaning process but with the use of suction equipment and low-pressure, forward-facing jetting equipment the contractor was able to remove this debris. A single patch repair was installed through the section of pipe where the obvert was missing this prevented further issues with collapse. Once secure and the PBF crews was happy with the pipe, the pre-liner was pulled into position. Once in place the initial Quick-Lock was installed from the down-stream chamber and locked into the pre-liner and pipe.
The rest of the Quick-Locks were all installed over a single 10 hour shift with a total of 28 separate Quick-Locks being installed on site by a small 3 person crew. Each Quick-Lock was overlapped with its predecessor to make sure there was a good seal and the additional strength that was required. The use of CCTV equipment and pulling the Quick-Lock and packer through the pre-liner by use of rope meant that the work could be completed very quickly and easily, reducing the risk of any further collapse of the pipe. The use of the pre-liner meant that installation through the excavation reduced the requirement to install new pipework which was necessary due to the potential risk of collapsing the existing downstream section. The void between the pipe wall and Quick-Lock repairs was filled using an injection grout that prevented and movement of the repair. Once completed the pipe was back filled correctly and re-instated into service.
The use of Quick-Lock and its mechanical sealing properties meant that there was no curing taking place which would all have added to the time on site and the risk of further collapse. The units’ strength meant that they could withstand the ground pressure and any backfill that was placed onto them.
PBF Drainage expressed thanks to Terry Ingleby and the project client for their trust to get the works done in a timely manner with the minimum of disruption, as well as cost effectively. PBF Drainage Services has developed a reputation across the UK for its high quality, diverse repair methods, working in sizes of 75 mm to 2,200 mm using the latest equipment and materials. Website: www.pbfdrainage.co.uk