Martin Knights provided the first of two presentations given to the British Tunnelling Society on 17 January 2002. Brown & Root (now Halliburton KBR) was awarded the role of Engineer on package 3 for the current CERN upgrade. Knights gave a brief introduction to the project, which was founded in 1953 and is funded by 20 European states. The new LHC project provides additional tunnels that link into the existing LEP (Large Electron-Proton Synchatron), which is an amazing 9km diameter ring. The current upgrade is to allow for the world’s most powerful particle accelerator to be constructed.

There are three packages of work within the civil engineering construction programme, with the third package sub-divided as shown in table 1. Martin went on to describe the tunnelling packages in which his company was engaged and to compare some of the different aspects between the roadheader excavated tunnel and TBM driven tunnel.

The geology of the area in which both tunnels are located consists of 2m-50m of moraine (quaternary glacial deposits of clays, silts, gravels and sands with occasional blocks of rock) overlying molasse (alternating sub-horizontal lenses of tertiary sedimentary material ranging from sandstone, 15MPa-35MPa, to soft sensitive marls of 16MPa compressive strength). In the moraine the water table is generally only 2m below the ground surface. The molasse is really impervious but some water and hydrocarbons are found in the sandstone parts.

The T12 tunnel was excavated using an AM-50 roadheader and the excavation was supported by a sprayed concrete and rockbolted primary lining followed by an in situ concrete steel shuttered final lining. The T18 tunnel on the other hand was driven with an open-type Robbins 116/189 rock TBM. In this tunnel about 55% was sandstone, around 35% was sandstone/marl mixed and the remainder was marls and superficial deposits. Primary support consisted of crown arches hung on Swellex rockbolts with localised steel lagging and, where required, sprayed concrete was also used. The final in situ concrete lining was similar to that for tunnel T12.

The graph shows the comparison between predicted and actual progress for each drive. Although for more than half its drive the TBM progress rate is double the typical roadheader rate, for the first five or six months they were quite similar. The problems encountered in this period were local heaving in the invert, shoulder spalling and crown instability requiring additional primary support. Applying the primary support behind the machine proved difficult and slow.

The FIDIC-based contracts were changed from the standard form to drastically reduce the programme and cost authority of the Engineer. This was because members of the main board of CERN represent 20 nations and only they had the authority to agree amendments to cost or time. However, there were many scope changes during the project because the scientists’ specifications for CERN were continuously changing. One result of the scope changes was a cost escalation of 42% in the first year. At this stage the Engineer was asked to develop a Supplemental Agreement as an incentive for the Contractor to reduce costs arising from scope changes. An open-book target-cost scheme to share cost savings (70/30) was developed where the Contractor’s overhead and profit were protected. Value Engineering workshops were used as the basis for agreeing the savings. The underlying spirit of co-operation since introducing the Supplemental Agreement has resulted in about 16% underspend compared with the targets, demonstrating the effectiveness of a collaborative agreement when the detailed workings are managed with care and sensitivity.

Lastly, Knights talked about some of the surprising benefits that CERN research has given the world. These included such things as the Internet, health research equipment including improved X-ray machines and TV technology.

Alpine approach

Paul Hoyland’s talk began with an explanation of his management of the tenders for Lötschberg and Gotthard Base Tunnels contracts on behalf of Balfour Beatty as part of a four-party joint venture with Marti (Swiss), Walter (German) and Porr (Austrian). He also explained how the Swiss terrain and weather had led to transport solutions predicated on tunnels with lengths which had dictated rail solutions.

To put the new tunnels into some context Hoyland briefly described the locations, dates and construction methods of the existing Gotthard High Level, Lötschberg High Level and Simplon Low level Rail tunnels.

The new AlpTransit (see T&TI November 2001) Lötschberg and Gotthard Base Tunnels will be 35km and 56km long, respectively. They will avoid the need for driving half way up the mountain (and half way down) with the shorter high level tunnels. The primary purpose is to provide faster transportation across the Alps, reducing the present level of road traffic and catering for future demands. It is estimated that the journey time will be reduced by about an hour. In conjunction with restrictions and tolls on foreign lorries, much of the freight should shift from road to rail. Paul then went on to discuss the Lötschberg Base Tunnel project in more detail.

There are two running tunnels for most of the route but at this stage, because of financial constraints, much of the western tunnel will be left “unequipped”. This includes omission of the secondary lining. The geology is generally good to moderately good quality crystalline rock but because of the great depth (up to 2km) there are high stresses and high temperatures to be overcome. The project is split into five contracts, with four main tunnel contracts.

The four-party JV (Arge Matrans) won both the Steg and Raron contracts by offering efficiencies from combining the two contracts. Each contract comprises a main TBM drive and a shorter length of drill+blast tunnel and both are due for completion in 2005. There are also cross-passages at 330m spacing between the running tunnels. The efficiencies of combining the contracts were summarised as:

  • all drives uphill;

  • more mechanised drill+blast;

  • eliminated interface;

  • combined spoil transfer from one portal by conveyor;

  • better use of equipment;

  • reduced offices and staff.

The type of contract was based on a traditional but very detailed re-measurement Bill of Quantities (B/Q), with the project being fully managed by the client and designer. The designer even specifies and designs all temporary installations (including underground batching plants) which have to be priced in considerable detail. Key interfaces are also specified. Each type of geology and ground support has to be priced; if the geology is different the programme gets modified. The B/Q also includes options (such as arches or rockbolts and shotcrete) which must be priced, with the decision on which is used resting with the client.

The TBMs are 9.4m diameter Herrenknecht side-gripper rock machines, each using sixty 17-inch traditional disc cutters. Each machine weighs 1,450t and has a back-up train 150m long. There are mechanised facilities for erecting mesh and arches and mesh is installed for worker protection, irrespective of the geology, for the whole of each drive.

The Steg progress has been quite close to that predicted being about four weeks behind with two-thirds of the drive complete at the time of the presentation.

The contract organisation follows European lines with site management reporting to a technical board which itself reports to a contract board. This has proved to be somewhat bureaucratic with decisions being slow. The site staff totals 42 people covering the 24-hour, seven-day working week for three drives. There are two working shifts and one maintenance shift per day. The workforce numbers 102 people including the 14 men per shift on the TBM.

Total spoil from the Lötschberg tunnel amounts to about 600Mm3. The spoil removal system for the TBM drives uses an extensive array of conveyors to feed the material to the existing railways to minimise the environmental impact of the cart-away process. Spoil is stockpiled in two tents to reduce dust and material wash-away. There are two conveyors feeding out underneath the stockpiles using a high-pressure air system to transfer material to the belts. The spoil is ultimately fed into a loading hall where the trains run through for loading.

An unusual feature for British tunnellers in the drill+blast drives is the hanging backup system. Rockbolts are used to provide hangers supporting the two overhead rails on which the backup runs. The benefits of the hanging backup were summarised as:

  • enabling faster production;

  • allowing all services to move forward with the face;

  • minimising tunnel construction traffic, providing greater safety;

  • allowing invert construction to be taken off the critical path;

  • allowing cross-passage construction to be taken off the critical path;

  • eliminating portal crusher, giving a simpler portal arrangement.

A track-mounted German crusher with a capacity of 450t/h is used within the tunnel. The crusher feeds to a conveyer in the hanging backup. Outside the portal, spoil is taken across a river to a reprocessing plant via an enclosed conveyer. Aggregate is produced in the reprocessing plant and taken back across the river on a lower belt within the same enclosed conveyor. In this way about 30% to 40% of the spoil is used as aggregate in the works. Some of it goes to a precast factory to make the precast concrete tunnel invert segments, the arch and crown final lining being by robotic placed sprayed concrete.

Paul closed his presentation with a summary of the “The Swiss Approach” to tunnelling. He said that the government is dedicated to providing a more extensive and efficient railway system with integrated transport solutions being considered for both the construction and operational phases of these routes. A traditional but fair style of construction contract is adopted with a considerable degree of detail, thereby reducing conflict.

High-tech methods are used where appropriate and this is facilitated by a positive attitude of being prepared to spend money initially in order to save money overall. With more sophisticated methods comes improved performance and reductions in the numbers of personnel. However, those employed are required to be multi-skilled. Prefabrication and recycling are maximised within a context of being fully environmentally aware and maintaining an interest in preserving the peace and beauty for which the country is so well known.

Related Files
Cross Section – Lotschberg Tunnel