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Murphy Pipelines Ltd uses Groundforce Rolling Strut to enable pipe installation
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Trenchless technology is no longer a novelty; everything from pipe re-lining to moling and micro-tunnelling is now routine in the utilities and related industries.
But that doesn't mean that progress has halted or that no further efficiencies can be gained, as Murphy Pipelines Ltd has discovered on its £23million Easington to Paull Gas Pipeline project for National Grid in East Yorkshire.
At 24 km in length, the Easington to Paull pipeline project is relatively short, however with 21 Major trenchless crossings & 4 Major Opencut crossings, & some 11km of difficult ground, the project has been technically challenging.
For Murphy Pipelines Ltd, construction is relatively straightforward: pipe sections of 12m and 18m in length are welded together into "strings" and then laid in a trench at 1.2m cover below ground level using sidebooms. Where the pipeline has to negotiate an obstruction, such as a road, river, existing service or in one case, a forestry plantation, Murphy Pipelines Ltd are using (along with other trenchless techniques such as Augerboring & pipe thrust) a "Grundoram"- a pneumatic ramming tool to drive pipe sections horizontally through the ground without disturbing the surface.
The ground in this part of Yorkshire's East Riding is soft alluvial clay, which Murphy Pipelines Ltd Senior Project Engineer Mark Gardner describes as "very soft - like butter". This makes for easy pipe-ramming (Mr Gardner says his team has achieved rates of up to 30m per hour on this project) but can present difficulties in supporting the sides of the excavations required to create the thrust pits for the pipe-ramming operation.
"The traditional options are to install a sheet-piled pit (cofferdam) or to batter the sides of the excavation to prevent the risk of collapse" says Mr Gardner. "Obviously the latter option is the fastest & most cost effective, but it's not always ideal and the soft clay doesn't react well with water, so we may well have had a problem if it had rained or we had encountered ground water" he adds.
But besides these two traditional options, Murphy Pipelines Ltd also had a third: to use a proprietary support system from specialist hirer Groundforce. This equipment, called the "Rolling Strut Double Slide Rail" is a modular unit designed for supporting deep excavations in difficult ground.
The system's single, moveable, strut allows maximum access for installation of long or large diameter pipes and maximum access for excavator buckets during installation, as well as affording good visibility for the operator.
Once installed, there is ample clearance beneath the strut, allowing for work to continue in the excavation without the hindrance of any obstructions."We had been thinking about using the Rolling Strut for some time" explains Mr Gardner. "We have several projects lined up where we think this may be a good option, but never had the opportunity to consider the system fully".
There were five obstructions along the route where ground conditions & crossing design suggested the use of the Rolling Strut Double Slide Rail to enable trenchless crossing. "So this was the ideal contract" says Mr Gardner.
Murphy Pipelines Ltd has used the Rolling Strut to enable pipe installation beneath four roads and one forestry plantation. In each case, four bays of Rolling Strut slide rails have been used to support a 19 m x 4.7 m x 5 m thrust pit. "The equipment is very quick and easy to use" says Mr Gardner. "Normally this kind of excavation would take four or five days to prepare using traditional sheet piled methods. It's finished in half that time using the Groundforce Rolling Strut."
Trevor Kendrick, technical sales representative for Groundforce in North and East Yorkshire, says the system is not only faster, but also cheaper than installing a sheet-piled cofferdam:
"I'm not just talking about installed costs, but up-front costs too. The equipment Murphy's are using at Easington costs roughly the same to hire as a hydraulic piling hammer.
If they were opting for a cofferdam, they'd have the cost of the sheet piles and bracing on top of that. I estimate the hire cost is therefore roughly half that of the traditional method".
Mr Gardner believes that systems like Groundforce's Rolling Strut Slide Rail will be more frequently specified in the future as clients demand more detailed temporary works design and method statements.
"These days we are obliged to provide our clients with all the designs and calculations for temporary works, so that we & they can be satisfied that we are constructing in a safe manner" he says. "Temporary works have become more important as safety continues to be the client's primary focus, & as a result they now get more involved".
Proprietary modular units such as the Rolling Strut Slide Rail are pre-engineered and far more straightforward than a bespoke cofferdam comprising many components. And of course, if a proprietary system can reduce the amount of work done on the site, that has huge benefits in terms of safety, as well as reducing installation times.
The pipe-ramming operation takes approximately 48 hours from start to finish, says Mr Gardner. Once the thrust pit is ready, the launch rails are installed and the Grundoram hammer welded to the first pipe section.
The pipe is then driven through to the reception pit which is opened up just before the pipe arrives; often no trench support is required here as the excavation is small and is immediately back-filled once the swan-neck has been welded onto the end of the pipe.
Murphy Pipelines Ltd has completed the 24 km pipeline in just twelve weeks, the project being mechanically complete during the last week in July. And according to Mr Gardner, the Groundforce Rolling Strut Slide Rails have been an unqualified success. "It's very quick, very efficient, and we've had excellent service from Groundforce. I'm quite happy to say it's exceeded my expectations" comments Mr Gardner
Contact Information
Lynn Campbell
TLC pr
Winslow House
16 Rumford Court
Rumford Place
Liverpool
L39DG
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