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Unique JCB machines keep Tyne Tunnel project on target

Leading North-East contractor, Holystone Ltd, has bought two purpose-built JCB tracked excavator models with unique boom and dipper configurations, to carry out specialist groundworks on the new Tyne Tunnel Project in Newcastle-upon-Tyne.

Wallsend-based Holystone Ltd has been awarded the earthmoving contract by the project’s main construction firm, Bouygues UK. In order to carry out the complex work, it has purchased a 46-tonne JCB JS460 tracked excavator with a Kocurek telescopic dipper and 1.5m³ clam-shell bucket and a 24-tonne JCB JZ235 zero tailswing model with a shortened Kocurek boom and dipper. The two machines’ unusual configurations were specified by Holystone and developed in conjunction with dealer Scot JCB Ltd and Kocurek.

Following the construction of the original Tyne Tunnel, which was opened in 1967 and which is used by up to 38,000 vehicles each day, this second vehicle tunnel is due for completion in 2010 and will run between Howdon, North Tyneside and Jarrow, South Tyneside.

The material the JZ235 excavates is collected by the JS460 - which is positioned above, at ground level. This larger machine uses its telescopic dipper to reach vertically down to depths of up to 20m and gather the excavated material in its clam-shell bucket which it then raises and empties into dump trucks to be taken away from the site.

Holystone Ltd’s Managing Director Kieron Geoghegan said: “Without these two tailor-made products, we could simply not meet the main contractor’s timelines for the project. Given the depth and space constraints of the working area the only alternative would be to lower skips into the open cut area using a crane. This method would have been far less efficient and would not have met the strict deadlines requested by Bouygues UK. Working in tandem, the two JCB’s are managing to remove an impressive 600m³ of earth per day.

"We have had several JS460 models before in harsh quarrying and waste management environments so we are aware of the machine’s excellent capabilities. The JZ235 is proving an excellent addition and our operators are raving about its performance. The reduced boom and dipper lengths combine to produce an incredibly powerful and productive machine while zero tailswing was a prerequisite for this role given the extremely confined working area.”

The two JCB machines are working in tandem on the north approach section of the project which will be constructed using a technique known as “cut-and-cover”. This will involve diaphragm walls being constructed underground, in order to create a supported space within which the tunnel excavation can be made. The diaphragm walls will comprise of two parallel, continuous, concrete underground walls. Once these are cast, the area between them will be excavated in a phased manner by the JZ235, and temporary struts placed between the walls for support. The short boom and dipper on the JZ235 create a reduced machine height of 4.7 metres which means it can safely work beneath the five metre high horizontal support struts.

The tunnel will then be constructed in situ, using base and roof slabs to provide lateral support. The temporary support struts will be removed as each base slab is put into place. Once the tunnel has been constructed, soil will be used to backfill the space above the roof slabs to create the necessary ground level above.

Part of the Holystone Group – which also boasts plant hire, waste and recycling and demolition divisions – Holystone Ltd specialises in a range of services including: drainage, road building, wet well construction, shaft sinking and tunnelling, pumping station construction, concrete structure construction and hard landscaping for leading civil engineering companies and local authorities. The Group operates a fleet of 30 excavators, 28 of which are JCB machines including mini excavators, JS220, JZ140 and JS460 models.