WET News

12 WET NEWS november 2015 A difficult 'pipe eating' project was undertaken recently to replace a 300mm diameter sewer with a 600mm diameter pipe – the ex- isting sewer was under capacity for its present requirements and was causing flooding upstream. The project, for Scottish Water, with Pipeline Drillers as the specialist contractor working for George Leslie, was located in Kingsknowe Crescent, Edin- burgh. The length of the section of pipe that needed to be replaced was 60m, with the existing pipe running at depths between 3.5m at one end and 6m at the other. Ground conditions comprised very stiff clay with boulders. The terrain also banked up and down along the full pipe length with the surface being mostly wooded, which added significantly to the access difficulties. The woods are also used by a special needs school under supervised access. Any works needing major surface access to the woods would have prevented use of the woods by the school for the duration of the project and for some time aŽer to allow the grass and woodland to re-establish. Access to the site was difficult with one end limited by the close proximity of a canal and a railway line whilst at the other end was the school. Taking these factors into account it became obvious that only relatively small size construction equipment could be used to complete the works. At the planning stage various options for the completion of the works were considered including Open Cut, Horizontal Directional Drilling (HDD), Standard Pipe Bursting and Auger Boring The Open Cut method was not an option as the location and route of the pipeline was more than 6m deep for part of its length and would have required the removal of trees. Also, there was potential for massive local disruption and environmental damage that such an operation would create. Overall, this meant that the cost of the open cut option was also highly prohibitive. HDD was also a non-starter because of the limited access and footprint at the installation site, which meant that there was little space for an HDD rig and its support equipment. Standard Pipe Bursting, whilst somewhat similar to the technique ultimately used, was not suitable because of the limited size of the equipment that could physically be used on site. A very large auger rig would probably have accomplished the drive but with weights in excess of 3,000kg and large excavations required, this option was also discounted. 'Pipe-eating' augers well for pipeline work ONSITE asset management The team opted to utilise an innovative combined auger boring rig and pipe burst rig assembly to complete a 'pipe eating' replacement technique. At one side of the run, where the existing pipe ran at 3.5m deep, a Perforator PBA150 auger boring system with 150t of thrust was used. At the reception end of the run there would be a Hammerhead 100t capacity HB100 pipe bursting rig, weighing just 1.3t, provided by U Mole. Struggled The maximum size of excavator that could access the site was a small 14t unit, which in the ground conditions sometimes struggled to achieve its operational requirements. The process of bursting the old pipe and replacing it with the new larger pipe is 'Assisted Pipe Eating'. With both the auger boring unit and the bursting rig positioned, a series of upliŽ pulling rods were passed through the existing pipe to connect the machines. The pipe-eating head was attached to the lead pipe of the jacking rig which also had a cutting ring on the front edge to aid passage of this pipe into the ground. The jacked and pulled pipe was a 762mm diameter steel pipe, which was to act as a permanent sleeve. With the new pipe and the U mole HammerHead Hb100 pipe bursting rig in position in the pulling shaft • replacing a 300mm diameter sewer with a 600mm diameter pipe in edinburgh soon turned into a challenge, with difficult site access putting equipment selection high on the agenda. 'Pipe-eating' replacement became the technique of choice. projEcT SpEcS replace a 300mm diameter sewer with a 600mm diameter pipe select appropriate trenchless technology TEchkNoW • a combined auger boring rig and pipe burst rig assembly was used to complete the 'pipe eating' replacement technique • the pipe-eating head was attached to the lead pipe of the jacking rig • a series of uplift pulling rods was passed through the existing pipe to connect the machines • the jacked and pulled pipe was a 762mm diameter steel pipe, which was to act as a permanent sleeve MoaNS & GroaNS • site access was difficult because of the close proximity of a canal and a railway line at one end and a special needs school at the other • the logistics were "nightmarish" because of the limits on equipment ThE VErDIcT • the carbon footprint of the works was reduced because of the trenchless technology • the innovative use of the combined jacking and pipe bursting systems brought success to a very challenging situation Confined access on site led to significant logistical difficulties throughout the project

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