Shani Wallis, TunnelTalk

Countries with the best infrastructure will have the best future - that could have been the theme for the tunnelling conference held in London this week (Tuesday, 29 Sept) where major urban projects were showcased. It was instead a statement by Martin Herrenknecht who opened the proceedings and illustrated how countries around the world are improving their national infrastructure systems using Herrenknecht TBMs of various sorts and sizes.

A slide show of major Herrenknecht projects illustrated the road through problems and improvements that have advanced the company's TBM technology arriving today at the machines designed for the challenges of the Lake Mead water intake tunnel in the United States (17 bar pressure design specification) and the Hallandsås railway tunnel in Sweden (100 litre/min water ingress at 13 bar pressure).

Alignment of Lake Mead's new intake tunnel

A most interesting slide came towards the end of the presentation when a map of the world with large circles drawn over the United States, Russia, Australasia, the Middle East and South America indicated the brightest spots for the company's foreseeable order books. Herrenknect explained that the US needs to invest heavily to improve their aging and under capacity infrastructure in all sectors - transport (urban and intercity), energy, water supply and sewerage; Russia, despite hard economic times recently, continues to plan major infrastructure projects across its vast territory; Australia and Singapore are investing actively in transport projects, and, quite astoundingly, 160 Herrenknecht TBMs are working currently in China with much more planned; Iran and the Emirates are busy in the Middle East; and South American countries, particularly Brazil, are beginning to sort out their economies, combat endemic corruption and put capital to work for the public good. No circle around Europe although Herrenknecht said in a teasing way; "This could change with Crossrail. It's up to you."

Lok Home was a fine foil to the Herrenknecht presentation - "We've had the soft, this now is the hard" - although Home stated that The Robbins Company is developing a range of soft ground TBMs to add competition to that rapidly growing market. In speaking about hard rock tunnels, it was confirmed that good, strong, competent rock comprises less than 5% of all 'hard rock' tunnels. More often the TBMs and their crews are having to deal with either loose, blocky or soft rock in the face, rock fallouts and overbreak in the crowns and sidewalls, and water ingress to flood proportions as experienced at the Parbati project in India.

Managing these issues was then matched to the different types of rock TBMs. Open main beam gripper machines have the advantage in that the rock can be seen and understood; the disadvantage being that supporting loose rock and applying support close to the cutterhead is difficult. A surprise admission from Home was that the distinctive finger shields of the Robbins grippers TBMs will be no more. They are often ineffective and frequently torched off by customers. Instead, a system of installing steel rebar rods into hollow channels in a TBM shield and strapping these back to the tunnel profile as the TBM advances has proven to be a much more effective system. Developed by Canadian contractor McNally for working through the blocky shale of the Toronto region, the system is licensed to Robbins and has been applied to good affect on the difficult Olmas project in Peru, described as being as, or more, difficult as the Gotthard tunnels with severe rock bursting problems under an overburden cover of up to 2,500m.

Using Olmas as an example, TBM tunnelling was still said to be the best choice over drill+blast - yes progress is only 4-5m/day in the bad reaches but drill+blast would not be doing better than that and the TBM turned in 600-700m/month in the better reaches. News of the Niagara tunnel was that better progress was being made now that the alignment has risen into the better sandstone that was encountered on the project's initial decline to get under the buried glacial gorge. The Arrowhead project in California was mentioned with the firm belief that it should have been a rock TBM project with the ability to provided easier access for drilling ahead of the face for water control grouting. Home also stated that all rock TBMs should be using 20in cutters. "They last longer and perform better that 17in cutters which should be retired."

Robbins 12.4m diameter TBM for Jinping

In speaking about Jinping in China, where Herrenknecht has one machine and Robbins has two including a 12.4m diameter TBM that launched recently, Home admitted that the rock support on the machine was not right and that modifications have been required on site. Against recommendation by Robbins to remove the ring beam erector, the client insisted that it be modified and retained. As part of the modifications Robbins also incorporated a pair of booms from which workers can better access the large diameter profile and apply immediate support more easily. But in speaking of ring beams Home was adamant. "Please, no ring beams in diameters of 8m and more." They are much too difficult to install and their effectiveness as rock support is minimal to nothing in such large spans. NATM support elements of rockbolts, mesh and shotcrete were said to be more effective and easier to apply.

Of the two shielded type TBMs Home said he is not a fan of single shield machines preferring instead the double shield system. Despite being shorter and providing for a quicker launch, single shields can only push off the lining and present little flexibility. Grippers in the double shields provide the option; allow for cutterhead pull back; and make possible concurrent lining and boring when using the grippers. The disadvantage is that probing is too far behind the face. These pros and cons lead to news that the Robbins team is working on development of what is the holy grail of tunnelling - an ACT - All Condition Machine. Details understandably were scant but an illustration showed a half shield, half open gripper type TBM with a wide 'free space' in front of the grippers to allow easier application of support and as close as possible behind the cutterhead.

To close, Home made a plea. "Let us please have better dialogue between consultants and TBM manufacturers before machine requirements are specified. A TBM specification is about six lines in a contract document, achieving it in practice can be impossible."

The programme moved next to detailed discussion of NATM or SCL tunnelling with some revealing information of its own. Alun Thomas spoke thoroughly about the design of SCL structures blowing first of all the "myth" of having to design for the full overburden pressure. Graphs of in-situ stress measurements confirmed that the load on a lining is never more than 70% of the full in-situ stresses. The discussion moved on to the economies of spray concrete final linings. With costs of about £45/m3 for in-situ concrete and about £110/m3 for spray concrete, the material costs are high but the savings are accrued in time, with substantial savings on project programme, and in materials consumption. If a single shell, load-sharing SCL final lining is adopted, a conventional reinforced in-situ concrete lining of some 600mm (300mm primary support + 300mm final lining) is reduced to a total 400mm single shell SCL permanent lining.

Ross Dimmock continued with the prospects for removing lattice girders as aids for controlling profile in SCL tunnels. A photo of the Hindhead SCL road tunnel in southeast England was used to illustrate how the profile was maintained to ±30-40mm on an 11m span without using lattice girders. The advance of shotcrete robots was reported with the holy grail here being the ability of the robot to spay to the profile as well as minimum thickness to compensate for uneven excavations. Spray-on waterproofing systems were highlighted as an extra tool in the arsenal for designing cost effective, quality long-term underground structure. The bonding of the spray-on linings to the primary lining and to the final lining was said to be the major advantage with effective surface preparation the key to the success.

An SCL alternative for top down excavation of escalator shafts presented the SCL option offering a flat invert across part of the excavator profile and an almost vertical face on the side as the incline goes down in rounds. A final consideration was for the use of shotcrete as the architectural finish of underground spaces with illustrations of glass cladding to side walls of a metro station, allowing the shotcrete to remain on show, and the shotcrete surface in another metro station being used as a canvas for local folk art.

Volker Wetzig of the Hagerbach Test Gallery in Switzerland spoke of the work being undertaken to develop new shotcrete techniques and materials, describing how mixes had to be designed to withstand 8hr travelling times on the Gotthard Baseline railway tunnel headings and application, once there, on rock surfaces with temperatures of more than 40°C. Wetzig also presented news about a polymer additive that will reduce rebound of shotcrete by up to 50%. This raised considerable interest but time was moving on and the presentation ended with emphasis of operator training and promotion of the EFNARC system of nozzlemen certification.

The entire session after lunch was dedicated to Crossrail, most of the 180-strong audience eager to know the latest. Chris Dulake, Client Package Manager with Crossrail Ltd for Tunnels, Shafts and Portals set the scene and Bill Tucker, Director, Tunnels, Shafts and Portals for the Bechtel, Halcrow, Systra Project Delivery Partnership describing in detail the procurement strategy. The most interesting points in Tucker's presentation included the following points:

• Tenders for the two big tunnel contracts under London (C300 Royal Oak Portal at Paddington to Farringdon and C305 Farringdon to Pudding Mill Lane Portal and Victoria Dock Portal) are to be invited by December 2009 and the contracts awarded by March 2010.

Crossrail's central underground route

• The first TBM is programmed to start on 15th Nov 2011 from the Royal Oak Portal at Paddington.

• Expressions of interest for the two big station contracts for C410 Bond Street and C420 Tottenham Court Road are to go out by December 2009, with tenders invited in March 2010 and award by June 2010.

• The intention is to have the station caverns complete for a 'walk' through of the TBMs when they arrive. For this reason Bond Street Station on the C300 tunnel contract is the critical path.

• Proposals from contractors to build both the Bond Street (C410) and Tottenham Court Road (C420) stations as one and with illustrated cost savings would be considered.

• A question from the floor asking if a proposal to combine the two first stations - C410 Bond Street and C420 Tottenham Court Road - with their linking tunnels contract C300, to avoid interfaces issues between different contractors, prompted a reply from Tucker that all possibilities were open to discussion but that

• the intent is to award the two big tunnelling contracts to different contractors.

• C805 is the one large muck haulage contract for transport by barge of all the central tunnel contracts from loading points along the Thames to a licensed disposal site on Wallasey Island in the Thames Estuary.

• There will be a separate contract for rehabilitation of the existing Connaught rail tunnel for incorporation into the project and this will be advertised in mid to late 2010.

• Invitation to tender the Thames River Tunnel to Woolwich at the same time as the two station contracts has been deferred to better suit project cash flow and capital draw down.

The schedules for bidding the other large underground elements were presented but furious note-taking failed to get the information scribbled down before the slides disappeared.

Bob Hogetts, Construction Manager, Tunnels, Shafts and Portals, explained that Crossrail has decided to specify the type of TBMs for the project. This follows the lessons learned on the earlier CTRL and JLE projects where some TBMs were "inadequate in power and performance". Hogetts explained that:

• EPB TBMs are specified for the central London tunnels with slurry TBMs for the Thames Tunnel.

• The EPBMs will be required to operate in full EPB mode at all times. No open mode operation.

• Two EPB machines are envisaged for the central contract C300 from Paddington to Farringdon Street Station and six EPBMs are needed on the largest contract of the project, C305 for the tunnels east from Farringdon to Liverpool Street and Canary Wharf.

• There will be no prequalification of the TBM manufacturers rather there will be a set of minimum requirements for power and performance.

• A two-part annular grouting gel is specified to be injected via a through the tail shield system.

• Steel and polypropylene fibre reinforced segments are being considered for the segmental linings.

Neil Moss, Crossrail Tunnelling Engineer, followed with a presentation about the requirements for monitoring ground movement over the underground excavation. Some 2,500-4,000 buildings lie within the corridor of influence. C701 is the contract to be awarded for managing data systems and run a central control room. Arup Atkins are currently working on the plans and specification of the needs.

Preparing a skilled workforce for building the Crossrail project and other major tunnelling projects, in the London and UK region, is the task of the Tunnelling Academy that is being sponsored significantly by Crossrail. Paul Chatten, Director of the Academy described how it will function and operate from its new base to be built in the East London borough of Newham. Some 14,000 workers will be employed on Crossrail at peak with some 3-4,000 of these involved on tunnelling and underground space contracts.

After a packed start of the day, three equally interesting and engaging presentations closed out the day. A paper about avoiding contractual disputes and claims by Michael Stokes and Garry Crossley was followed by a comprehensive report on the design and on-going construction of the 46km long Line 9 project for the Barcelona Metro. Engineer Nicola Della Valle described in particular the method by which the station platforms are built into large diameter running tunnels. The tracks and the platforms sit one above the other with an adjacent access shaft, of significantly smaller proportions than an open cut station box, providing access to the surface.

The final presentation was an engaging telling by Colin Eddie of the ups and downs of the Croydon cable tunnel project by Morgan EST. From the need for special consideration to avoid disturbing ground water aquifers, to no escaping a down hill drive of 10km long, to the incredible inflow a 100litre/sec of ground water through a fissure in the chalk geology that needed control by intense pumping to get through the water inflow reach into a reach where the water disappeared as quickly as it had appeared. The drive was successfully completed and the tunnel is now being fitted with the 400kV electric cable and a man-rider car that travels the 10km cable tunnel on a monorail attached to the crown.

The Lee Tunnel is the first of the Thames Tideway tunnels to bid

As well as the fast moving conference sessions there was an exhibition of some 20 stands representing major suppliers and service providers to the tunnelling industry. During a coffee break among the stands, and while there was a lot of anticipated excitement about Crossrail, there was also concern about the delay in awarding earlier tunnelling projects. Colin Eddie for example, explained that Morgan EST had submitted tenders for about £1 billion of work during 2009, include the Lee Tunnel for the Thames Tideway CSO sewer project in London and other cable tunnels, none of which have been awarded. Eddie also explained that once the company's job in Belfast, Northern Ireland holes through in the coming weeks, it will be the first time in 50 years that the company is not actively excavating a tunnel. Finishing off tunnelling contracts yes, but not actually operating a TBM or advancing SCL work.

Much hangs on maintaining the momentum of Crossrail and getting the contracts awarded to keep a tunnelling capacity in the UK. The hope is that next year, when a similar conference might be co-sponsored by the BTS (British Tunnelling Society), there will be more to celebrate and more tunnellers in town and working on London and UK projects.

References:

Lake Mead Intake No 3 - TunnelTalk, June 2008
Crossrail management mobilized - TunnelTalk, May 2009