West East Link Main

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West East Link Main

Shaft Construction and Tunnelling works

Principle Contractor: Murphys

Client: United Utilities

ATL Scheme Ref: 284

 Click here for a feature on West east link main

Summary

Numerous road, rail & river crossings are required along the length of the new 56km, 1200dia West, East link water-main, being installed by MPL. To prevent disruption & aid in the ease of installation of the water-main, some of these network crossings are to be constructed by installing a reinforced concrete sleeve via pipe-jacking methodology. The water-main is then pulled through the sleeve from one side of the crossing to the other. To enable the pipejack works to be carried out, deep, concrete, segmental shafts are constructed either end of the drive by caisson sinking or underpinning methodology.

Active tunnelling has carried out the following Specialist Tunnelling works to date on the WELM scheme:-

Segmental Shafts

ATL have sunk three number segmental shafts, all 7.5m diameter, varying between 19m-26m deep, using both caisson & underpinning methodology. This has been through varying ground conditions, from clay, to running sand to very hard rock & at times a high water table to deal with.

Long reach excavators with clamshell grab attachments where used where possible and excavators where lowered into the shafts with breakers, when rock was encountered. The shaft works where serviced via 50ton crawler cranes for raising & lowering equipment & muck skips to & from the shaft formation.

Pipejacks

Due to the hard nature of the ground to some of the pipe-jack crossings ATL were called upon to use their own specialist "road-header" tunnelling shield to dig out the rock/ mudstone at the face of the tunnel, whilst using traditional pipe-jacking methods to push pipes behind. To date ATL have carried out two successful tunnels using this method & are currently half way through another. The first crossing was just over 200m in a mudstone/ sandstone strata, with the second crossing being 175m in very hard clay. We are encountering rock & mudstone on the current drive, which will be an impressive 365m long when complete.

Strongford STW 1500, 1800 and 2100 mm ID (Black and Veatch)

The work consisted of linking 4nr insitu concrete tanks together with 4nr 1500mm diameter pipejacks and a 2100mm diameter pipejack. The average length was 40m.

The second phase was to mitigate a deep opencut and maintain access within the works. The work consisted of a 2100mm pipejack 180m long in mudstone. ATL utilised their own 2100 backactor to carry out the work to programme and within budget.