Wilkinson Environmental - Drain and Sewer Obstruction Removal of Circular Steel Pile

  • Client: Wilkinson Environmental
  • Service: Drain and Sewer Obstruction Removal
  • Industry: Civil Engineering
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Whilst most drain and sewer blockages are dealt with using water jetting, on occasion the obstruction is too difficult to remove simply by hydroblasting and requires an advanced cutting solution.

In this instance, RGL were tasked with removing a 300mm circular steel pile from inside 375mm diameter clay sewer. With the obstruction lying 20 metres from the nearest access point, it called for an ultra high pressure water jetting unit (2,800bar) and bespoke abrasive water jet cutting nozzle, mounted on a self-locating hydraulically powered manipulator to reach the workface.

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This project posed a very difficult and unique challenge to all involved. The pile had been driven through a clay sewage main, and had to be removed in order for the works to be completed. The pile had been driven through a clay sewage main, and had to be removed in order to restore sewage flow. Access points being 20 metres from the obstruction upstream and 60 metres away downstream. Abrasive water jet cutting method had been selected for its ability to cut thick composite materials. It is a heat and spark free process so there would be no risk of explosion, should volatile gas be present and the equipment could be operated by remote control, making it an ideal solution to this complicated cutting task.

The challenge for the RGL Technical Team was to develop custom tooling which would enable remote control cutting of the pile without causing further damage to the pipe. The design and development team consisted of the Development Director and Technical Support Engineer who adapted an existing system which RGL use to cut circular piles internally in marine applications. The new equipment needed to be smaller in size to fit in the sewer main. Further adaptations were required to enable the flow of cutting abrasive and UHP water to travel horizontally to the work face. The sewer pipe had sustained significant damage where the pile had been driven through it. Once cut the loose pile section was to be recovered by the Wilkinson Environmental Team using HP Drain Jetting and mechanical winching.

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The Cutting Nozzle had to be set carefully at the correct angle to ensure the pile; together with the concrete inside, would be cut without causing damage to the fragile clay sewer pipe.

Following camera surveys which were previously conducted by Wilkinson Environmental, the exact position of the pile was established and a plan of action was agreed.

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RGL worked with Wilkinson Environmental to formulate the program for the works; work was undertaken during night shifts (10pm-4am). This was due to the works taking place on a busy road within Coventry. Once the approval had been granted from the Highways Agency and all traffic management had been arranged, the works were ready to begin.

On the first night of the project RGL arrived on site to familiarise themselves with the working area, and proceeded to set up all the required equipment including the ultra high pressure jetting unit, fuel and water supply. They also ensured that the temporary over pumping of sewage flow was working adequately. Due to the limited working hours available there was inadequate time remaining to feed the abrasive jet cutting manipulator into place. It was agreed the cutting works would start the following night.

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The second night saw work commence at 11pm, and due to the preparatory works of the previous night, RGL were able to immediately start lowering the cold cutting unit into the sewer with the help of Wilkinson Environmental. The manipulator was then pulled along the sewer approximately 20 metres (from the upstream manhole). Once positioned next to the encroaching pile the unit was secured into position using the hydraulic stabiliser; this meant there would be no movement of the rig during the cutting work as, in order to achieve the cut, the water jet head must traverse in one continuous and smooth motion.

To offer greater accuracy it was agreed that the CCTV Camera would be fitted to the cutting unit. This would enable the operator to watch the cutting in real time and achieve a high level of accuracy. The camera enabled RGL to fine tune the amount of grit feed, stand-off distance, nozzle traverse rate and proximity of the cutting head.

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During this first shift of cutting a partial cut was achieved.

During the fourth night the complete cut was successfully made with total penetration through the steel pile casing and concrete infill. RGL removed their cutting equipment and Wilkinson Environmental used a high powered drain jet to dislodge the cut section of pile. They verified by CCTV that the section was loose and had been suitably dislodged.

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With the pile now cut RGL left site. Wilkinson Environmental then continued with their work to remove the cut pile and install a structural patch repair over the damaged pipe section. As can be seen in the adjacent photograph the finished repair restored a virtually complete full bore to the pipe. Despite the challenging nature of the work the project was a great success.

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