Yarl Hydracentre in conjunction with BAM Nuttall designed and manufactured the hydraulic power unit used to push the complete tunnel structure 50m from its construction site adjacent to the embankment. The technique is known as box jacking.  The completed tunnel structure sits on a low friction foundation which also forms the reaction block from which three sets of six hydraulic cylinders drive the completed tunnel structure forward into the embankment. As the tunnel structure moves forward the embankment material is excavated away.

Key attributes of the Yarl Hydracentre design were to provide a compact self contained power unit offering a number of risk reducing features. The jacking process had to be completed and this rail line, key to the UK rail network, had to be active again in just three days. At the heart of the power unit was just a single 37KW pump set capable of moving the vast 5000 Tonne structure alone. This was backed up by a second 37KW unit in case the first failed. A third 75 KW pump set was employed, capable of generating 700 Bar at the full flow rate of 40L/min. This unit was selected to generate additional force in the event of the embankment material closing in on the structure in mid push.

Yarl Hydracentre technicians supported the whole continuous 3 day and night box jacking process ensuring the structure maintained constant progress. We are please to say although many modes of failure were considered and the risks mitigated the power unit performed to plan only requiring the single 37KW pump set to generate the motion.

The power unit was design and manufactured at the Yarl Hydracentre facility in Barrow in Furness, The three sets of nine hydraulic cylinders used to generate the thrust had been used on previous box jacking projects and were reconditioned by Yarl Hydracentre. The complete power unit and cylinder set was tested in Barrow prior to shipping to the Tipton site.

For further information on engineering services from Yarl Hydracentre please contact    

Barrow 01229 845 560

Workington 01900 734 730

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