Why Tunnel vision requires flexible boring

United Utilities' ambitious West East Link Main has needed highly specialised tunnelling techniques. On behalf of Tunnel Engineering Services, Ian Clarke describes two challenging boring drives

Why Tunnel vision requires flexible boring

United Utilities' ambitious West East Link Main has needed highly specialised tunnelling techniques. On behalf of Tunnel Engineering Services, Ian Clarke describes two challenging boring drives

As part of a £125M project being undertaken by United Utilities known as the West East Link Main (WELM) (see WWT February), Tunnel Engineering Services (TES) recently provided five tunnelling machines for the completion of various tunnelling sections of the work.

The WELM is a pipeline that will carry water right across North-west England, from the Prescott Reservoir in Merseyside to the Woodgate Reservoir in Bury. The main contractor appointed to complete the works is J. Murphy & Sons.

The project will see the installation of some 54.5km of 1,200mm diameter welded steel pipeline which is designed to transfer up to 100Ml of potable water, in either direction between the reservoirs every day, to safeguard water supplies to the catchments at either end of the supply line.

Tunnelling and trenchless techniques were necessary because at various points the pipeline passed under various roads, motorways, rivers and railways. The route also crossed areas of contaminated ground and some of significant environmental concern.

One of the machines used, was a TES 1800. Earth Pressure Balance (EPB) TBM, owned and operated by B&W Tunnelling. TES can manufacture this type of machine in diameters from 1,200mm, to the power, torque and cutterhead configuration required by the client for specific projects.

Adaptability
The specification for the TES 1800 EPB TBM for the WELM project included the ability to set the machine up for an 1,800mm internal diameter pipejack, with an adaptation which would allow the erection of segment linings if required.

The machine was fitted with a carbide insert mixed-ground cutterhead and supplied with a spare rock head, push cans, gripper/anti-roll cans as well as the segment erection adaptation. The power of the machine was 195kW with facility to operate the cutterhead at between 0 to 9.5rpm. The machine was designed and manufactured by TES in 16 weeks.

Variable ground
Using the TES 1800 EPB TBM, the first drive on the WELM project required an installation of some 470m. The ground conditions on this drive comprised mainly mudstone and weak sandstone.

The carbide insert cutterhead was designed to handle these expected conditions. During the course of the drive, the machine unexpectedly encountered a more competent rock strata.

The TBM's high cutterhead torque and cutter power enabled the machine to successfully handle the harder ground conditions without the need to modify the cutterhead in the ground. It still managed to achieve up to 25m of advance in a 24-hour shift period.

The second pipejacked tunnel undertaken with this TBM was driven entirely through a solid rock mass. Knowing this, the TBM's cutterhead was reconfigured prior to the start of the drive, with disc cutters being interchanged for the carbide insert configuration used on the first drive. In this instance the drive length was 660m, with a production rate averaging some 20m in a 24-hour shift period. All drives undertaken on the project to date have been successfully completed.

TES managing director Geoff Clarke says: "Our design of the TES 1800 EPB TBM has shown its flexibility and durability throughout the course of the WELM works. The ability to interchange the cutterhead configuration for the varying ground conditions proved very useful for the second drive.

However, most pleasing from our point of view was the machine's inherent ability to handle the unexpected harder ground encountered during the course of the first drive, proving the underlying strength and power built into the basic design."

Steve Williams, managing director of B&W Tunnelling says: "I am delighted with the performance and reliability of the TBM. Tunnel Engineering has given an exceptional delivery on the machine and has the flexibility to ensure that the equipment was delivered on-site to our special requirements."

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