Crossrail sets up for first drives from the east
Jul 2012
Patrick Reynolds for TunnelTalk
- Last week saw the cutterhead and screw conveyor fitted to the first of the two Herrenknecht EPBMs that will undertake the longest of the Crosrail running tunnel drives below east London. At the same time production was gearing up at the casting yard for supply of segments for the 6.2m i.d. tunnels to the Dragados/Sisk JV Contract C305.
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Main Limmo launch shaft
- To the west of the capital the second of a pair of Herrenknecht machines, working from the Royal Oak portal near Paddington, has just got under way for the BAM Nuttall/Ferrovial Agroman/Kier JV for Contract C300. TBM 2, Ada, has just started, while TBM 1, Phyllis, has progressed almost 400m since its launch two months ago.
- Back at Contract C305, Dragados/Sisk will lower and launch the first of its TBMs, Elizabeth, from shafts built at Limmo, construction of which recently reached the temporary bottom levels. At that depth a pair of approximately 8.6m high x 8m wide tunnels are being excavated between the 30m wide permanent shaft and the 27m diameter auxiliary shaft to hold each TBM, bridge and 10 gantries.
- The 7.08m diameter Herrenknecht EPBM is to be launched in November, to be followed a few months later by its sister machine, Victoria, which is scheduled to arrive at Limmo for assembly following shipment from Germany and transfer from Tilbury Docks. After launch the larger shaft will be completed to its full depth of 44.8m.
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Fig 1. Plan of the Contract C305 TBM drives
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Fig 2. Crossrail's longest Drive Y tunnels ready to start
- The combination of two shafts allows for an "efficient launch" of the TBMs, said the client's C305 Project Manager, Peter Main. Most of the back-up will be in place, enabling continuous driving along the alignment near the river.
- The shields will bore the project's longest 8.3km long Drive Y tunnels (Fig 2), taking them west through the Canary Wharf Station, Stepney Green junction, and then on to Whitechapel and Liverpool Street Stations before terminating at Farringdon Station (Drive X, Fig 1).
- Works are also under way at Limmo to construct the reinforced concrete slab to hold delivery of segments for the 6.8m o.d. segmental lining. These are being manufactured at a dedicated casting yard in Chatham on the Medway River Estuary in south east England. Seven of the 300mm thick segments plus a key will form each 1.5m long ring. The production facility came online in early July, a little ahead of schedule, said Main. He added that full production is to be reached next month.
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Assembly of TBM Elizabeth at the Limmo job site
Photo by: Patrick Reynolds - Dragados/Sisk has had early access to the Canary Wharf box station to prepare to receive and pull through the TBMs next year. Early access to the station was possible as construction of Canary Wharf is months ahead of schedule.
- Once relaunched, the shields will reach and transit through the Stepney Green box structure next year. The box is approximately 60m long x 15m wide and is to be expanded to form the turn-out junction between the Y Drive and the 2.72km long Z Drive branch off to the Pudding Mill Lane portal, which leads on to Stratford (Fig 3).
- Almost two-thirds of the 35m deep junction box has been excavated, and within the next few months the contractor will start break-out to construct large, 30m wide x 17m high interlocking SCL caverns that will form the junction space. The primary lining will be 200mm-250mm thick shotcrete and will stand alone for about two years before casting the secondary lining, which is to be up to approximately 170mm thick.
- To be excavated in clay, such rail junctions in London would have been constructed as step-plate junctions in decades past. A major reason for the possibility of using SCL for such significant tunnelling in an urban setting is the advances in measurement control in recent years, explained Main. He added that the SCL works provide the most flexible float within the C305 construction programme.
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Fig 3. Drive Z Pudding Mill to Stepney Green
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Fig 4. Short Drive G tunnels finish C305 TBM bores
- The TBMs that will bore the Z Drive will be launched at Pudding Mill Lane portal. Works at the site are currently slowed, as planned, due to the Olympics. The machines will terminate in the caverns at Stepney Green junction in the second half of 2014. The first machine removed will be reused to bore, in turn, each of the 930m long G Drive tunnels between Limmo and Victoria Dock portal (Fig 4).
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Base slab at Limmo built to hold tunnel segments
Photo by: Patrick Reynolds - Separately, the Stepney Green caverns are planned also to remove the 7.1m diameter cutterheads from TBMs Elizabeth and Victoria after they terminate at Farringdon. The TBM shield parts and backups are to be taken back to Limmo for recovery.
- The various stretches of running tunnels along the C305 package are to be linked by 10 cross passages, seven of which are to be lined with SGI rings, and three constructed by SCL. Five of the cross passages will have sumps, and the section will also have a niche sump.
- Two 30m deep ventilation and access shafts are to be constructed on the Stepney Green to Pudding Mill Lane branch, at Eleanor Street and Mile End Park. Contract C360 for these works was awarded in May to the Costain/Skanska JV.
- Contract C340 for construction of the Victoria Dock portal was recently awarded to Vinci Construction.
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Maiden Crossrail TBM to launch sets off - TunnelTalk, March 2012
Herrenknecht begins roll out of Crossrail orders - TunnelTalk, December 2011
All Crossrail TBMs in the Herrenknecht basket - TunnelTalk, September 2011
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