Large Upsize Pipe Replacement Beneath the West Highland Railway

A view into the deteriorated clayware culvert being replaced.

A HammerHead HB125 static pipe-bursting system, provided by U Mole (a division of Vp plc within Groundforce) was recently utilized by rail contractor Carillion to undertake an interesting and challenging project to replace a 450 mm i.d. clayware sectional culvert running beneath the main railway line between Crianlarich and Oban.

Running at around 5-m depth the 450-mm existing culvert needed to be not only replaced but also up-sized to 630 mm with the replacement pipe being HDPE. While the project at first appeared to be a straight replacement job, with the need to utilize a 730-mm diameter expander behind the bursting head, an equivalent up-size of over 250 mm diameter, the installation of the new pipe was not going to be easy.

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Although the contractor had used the Hammerhead HB125 on an earlier section of works on the West Highland rail route, given the massive up-size required for the new installation, operator training of Carillion personnel was completed by U Mole engineers prior to the works on site at project site at Taynuilt.

The new HDPE pipe being prepared for the bursting run. Inset: The bursting head and expander shell.

Other parts of the challenge on the Taynuilt site over and above the up-size required, was access and site preparation. To achieve the replacement installation site works were undertaken for 14 days before the bursting work could commence. This was because ground conditions at the site proved to be soft which meant the footings for the pipe bursting system had to be correctly constructed. The site also required the removal of a line of trees in the rail embankment. These site preparations of the launch and burst site had to be completed with imported stone etc. Also required was the environmental protection of local waterways in case of any hydraulic leaks etc.

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Once the site prep was completed the job could be started. Carillion’s workforce was ultimately delighted at the ease of operation of the bursting system once set up. The bursting works, including machine set up were completed over the course of just two days. The actual simultaneous burst run and new pipe installation were actually completed in less than half a working with day no disturbance to the railway line on the embankment above. Looking ahead to a series of future bursts beneath the railway line members of the crew commented that they were looking forward to once again using the HB125 system.

In terms of the site setup, another complication that was faced by the contractor was ensuring that launch pit face was able to resist the pulling forces of the bursting rig. Carillion’s Section Engineer for the works, Glen Henderson, had to develop a temporary jacking face system that was capable of distributing the pulling force of the rig against the relatively soft railway embankment. Henderson said: “Due to the added resistance caused by the expansion process when bursting the existing pipe, the pit face had to be very robust. The set-up ultimately consisted of driven sheet piles with 13-mm (½ in) thick steel road plates.”

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Works were carried under the normal working times of the trains. RETB tokens of the OBN2 line between Dalmally station and Connel station were taken and pipe pulling operations to install the new pipe took place between trains. The contractor also continuously monitored the cant and level of the track so that the works could be stopped at the first sign of any movement. The depth of the fill between the pipe installation and the track allowed sufficient consolidation through the embankment such that during the operation no track movements occurred.

Henderson went on to say: “Due to the depth of this culvert below the track level, the traditional deep excavation and replacement would not have been feasible. With guidance and training from U Mole, we were able to exploit the benefits of trenchless technology. We were able to cut down on our material usage in terms of not requiring substantial amounts of backfill and we minimized our wastage by having no excavated material to dispose of. Any opportunity where we are able to keep the railway open to traffic while undertaking this type of work puts us ahead of our competition and allows us to achieve a more economical and sustainable end result for both Carillion and ultimately Network Rail and the service’s customers.”

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The new pipe entering the now burst clayware pipe during the bursting run.

The Hammerhead HB125 static pipe-bursting system offers contractors one machine that is versatile enough to replace a wide range of water, sewer and gas pipelines ranging from 150 mm (6 in) to 500 mm (20 in) diameter. Designed with production in mind, the HB125 offers 113 t (125 ton US) of pulling force.

A simple one-man operation, with on-board rod basket and 19 second rod payout, the HB125 has five hydraulic stabilizers for leveling and rear jack adjust to place the machine on grade and aligned with the existing utility. Adjustments can be made during the burst as conditions change without stopping the bursting process.

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HammerHead uses a heat-treated alloy rod. The API-style joint handles thrust loads encountered when pushing around sweeping bends and encrusted or collapsed pipes compared to loose joint rod designs, which can buckle in such conditions.

The Hammerhead® HB125 bursting machine set up and operating at the launch site during the bursting run. Note the reinforced thrust wall at the face of the launch pit.

While not used on this particular project, Carillion’s HB125 unit also has the facility to utilize rotational torque assist which can be a key to the success of many schemes. The HB125 is the only pipe-bursting machine that offers the combination of thrust and rotational torque during payout to allow operators to push and rotate a drill head or lead rod through collapsed or encrusted pipes.

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Other features on the HB125 include a rod lock device which places constant tension on the pipe string eliminating rod rebound thereby increasing production. An auto rod spinner also quickly makes and breaks joints with and helps to increase overall production.

For equipment supplier U Mole, Frank Gowdy, sales and marketing director said of the Taynuilt project said: “This is exactly the sort of project the Hammerhead HB125 is designed for. Its power and versatility is precisely what was needed for this type of replacement job. The machine capacity is now being well proven on replacement works under the West Highland line and, as on an earlier project, the additional availability of the rotational component to the rod insertion phase can enable this unit to handle particularly challenging circumstances. While it was not needed at Taynuilt, it was always good to know that the capacity was there should it be required.”

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The bursting head emerging at the launch pit at the end of the burst run which took less than half a working day to complete.

U Mole, a division of Vp plc company Groundforce, is the direct factory UK and Ireland distributor for Earth Tool equipment offering the company’s full range of products for trenchless installation and pipeline replacement. This range includes impact moles (earth piercing tools), pipe ramming hammers, twin capstan winches, static rod pipe bursting systems and the portable cable-based, hydraulic pipe burster range.

U Mole also supplies a full and extensive range of trenchless and limited dig equipment including: Suction/vacuum excavation systems (including MTS systems alongside Vac-Tron systems) and surface coring equipment for the ‘Keyhole’ excavation of utilities and services with minimum disruption to the local area and minimum damage to the buried service. Other trenchless related equipment available includes the market leading Robbins SBU equipment, Pipe to Site coiled pipe trailer range, pipe fusion systems, Reed Tools and a complete range of accessories such as Cobra flexible rodding, towing heads, cable socks, pipe pigs, swivels, breakaway connectors etc.

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This article was supplied by U Mole, based in Cambs, United Kingdom.

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