Long base railway ambitions in Switzerland Mar 1994

The predominant underlying message delivered to Germany's STlNA conference in Hamburg in November 1993 was that Europe must build tunnels faster and cheaper. While the statement is something of a truism, it takes on greater significance when applied to Switzerland's current plans for long base line railway tunnels through the Alps.

Although improved tunnel design, together with fierce competition and increased automation, is tending toward more efficient use of more highly qualified labour and has induced more cost effective tunnelling over recent decades, it is the size of future projects and the impact of their construction period on project funding which renews calls for greater speed and efficiency. There is also increased concern for the health and safety of labour given rising costs of compensation.

Lower set of grippers on the 7. 64m diameter Wirth TBM launched on the Zugweld tunnel of the Vereina railway tunnel project in Switzerland

Alpine base lines

Switzerland's Neue Eisenbahn Alpen Transversale (NEAT) or base line railway strategy to improve the rail services on the St Gotthard and Liitschberg/Simplon rail lines is motivated politically to preserve the country's 28t limit on road freight against the standard 40t of European Union (EU) neighbours. The plans call for up to 95km of tunnels on the Gotthard line and another 40km of tunnel on the Lotschberg/Simplon line. The longest tunnel will be the St Gotthard at more than 50km from portal to portal, followed by the Lotschberg at 35km; the Ceneri at 12km; and the remainder at between 2km and 8km.

At present, the preliminary design and feasibility studies for the project have been completed resulting in a treaty of federal government approval signed in 1992. Engineering groups are now tendering for the detailed design lots which are expected to be announced in Spring 1994. There are 14 engineering lots for the two lines in total, five of which are for detailed tunnel design. To handle the enormous scope of the NEAT task, Switzerland has opened its otherwise largely protected domestic construction market to international competition. Some 300 engineering groups submitted prequalification documents for detailed design. Those accepted can submit a tender for up to four lots. A short list of five tenders (70 groups) will then be called for discussions before each design lot is awarded.

Although approved in principal, local communities, which have a right to oppose the scheme, are consulted during the detailed design phase. For this reason, the final location of portals and therefore the number, alignment and length of tunnels involved is still far from confirmed. Contracts on the Gotthard line are with the Swiss National Railway Authority, SBB, and with the Bern-Lotschberg-Simplon Railway on the Lotschberg route.

The feasibility and preliminary design work for each Base Tunnel has been undertaken by two engineering groups. Swiss consulting firms Amberg AG, Electrowatt AG and Lombardi SA worked on the Gotthard. This same group has now tendered for four of the five detailed tunnel design lots. The Lotschberg/Simplon line studies were carried out by the Emch & Berger AG, IUB, Bonnard & Gardel SA, Schmeller, Schmidhlter und Ritz AG group.

While there are some fundamental differences between the tunnelling required on each line, the basic engineering philosophy and principal concerns are applicable to both. A visit to Switzerland in December 1993 provided the opportunity to interview Mr Felix Amberg, chief engineer of Amberg AG and son of the company's founder, who discussed some of the more challenging aspects of the project with reference particularly to the St Gotthard line and tunnel.

The base line railway links are motivated principally by environmental and political rather than economic reasons. Although rail carries a higher percentage of freight in Switzerland than France and Austria (about 10- 15%), Swiss railways operate, like most, in the red and are heavily subsidised by the government. Economically, the project will bring a huge back payment on investment which rail companies will find difficult to support on current income. The cost estimate for the St Gotthard Line alone is SFlO billion using 1991 as a price base and excluding inflation and financing costs. Of this, the estimated turnout cost for the 57km long Gotthard tunnel is SF5 billion excluding inflation and financing. Swiss bank lending rates in December 1993 were 7-7.5% which do not present a very attractive proposition if it takes 60 years or so to recoup the enormous costs. There is also doubt about the revenue base given the shift in the principal axis in Europe back to an east-west rather than a north-south bias since the reunification of Germany and the collapse of Communism.

The viability of the project therefore depends on maintaining the 28 t road freight limit and ensuring that heavier freight goes by train. A referendum in February 1994, proposes forcing all transit freight onto the railways. If passed, this will greatly improve the viability of the project and generate greater interest from financial institutions, but will result in a more complex position of Switzerland in its negotiations with the EU. Having approved the project in 1992, the Ministry of Transport set a target opening date of 2007 for the St Gotthard Base Tunnel. This squeezes tunnel excavation, the most time-consuming portion of the civil works, into a tight 11 year schedule with tunnelling starting in 1996. It is on this that all project planning and scheduling is being based.

TBM tunnelling

By drawing on current tunnelling expertise, it is agreed that most of the tunnelling through the gneiss and granite rocks of the Alps will be by full face hard rock TBM. While drill+blast will be more applicable in some sections, particularly those expected to present the most difficult geological conditions, TBMs can progress faster than drill+blast in favourable rock, require less labour, and TBM tunnelling costs are easier to forecast and schedule.

Fig 1. Switzerland NEAT railway strategy is designed to improve the rail freight and passenger services across the country between its EU neighbours by excavating long base tunnels through the Alps on the St Gotthard and the Lotschberg mountain pass routes

Even so, the project takes TBM tunnelling to a new dimension. There is a high content of quartz in the granite and gneiss, the rocks have unconfined compressive strengths of up to 250MPa, and work will progress under extremely high overburden of up to 2,500m. "Cores of up to 850m deep taken from the surface indicate that there will be severe rock stability problems with high deformation and rock bursts and the potential for very high volumes of groundwater ingress, probably at high pressures," said Mr Amberg. "Natural gas is also a possible problem in the Lötschberg tunnel, but not in the St Gotthard."

There are three major zones in the Gotthard base line tunnel where extremely difficult ground conditions are anticipated, the worst of which is the Piora Mulde, an unstable sedimentary rock. An advance geological investigation tunnel is currently underway to examine this zone in particular (see yellow box). So far, some SF100.150 million has been spent on preliminary site investigation work for both lines, excluding the SF40 million investigation tunnel contract.

Given all these concerns, as well as discussions about subsequent operating safety, it was decided that the long tunnels would comprise two single track tubes with intermediate crossover facilities and without an associated service tunnel. This gives the tunnelling machines an outer diameter of about 9m. A double track, single tube configuration would have required TBMs of 11.5-12m diameter. Discussions with major TBM designers confirmed that at more than 7-8m diameter, the TBMs will require the most advanced TBM technology anyway and that using larger diameter TBMs on this project, while perhaps technically possible, would involve enormous risk. It was agreed that, had a double track, single tube configuration been acceptable on other levels, all tunnelling would have been by drill+blast. As it is, the TBMs will have to be designed and equipped to install efficient immediate support measures as well as provide maximum reliability and performance.

Single shell lining

Greater viability of the project also hinges on proposals to adopt a single shell shotcrete lining in the tunnels. Traditionally, hardrock tunnels in Switzerland, particularly those excavated by drill+blast, have been finished with an in-situ concrete lining, often reinforced and designed to carry the entire anticipated load. All immediate or primary support was considered temporary and therefore sacrificial.

Attitudes and technology have changed in the meantime. A final lining is now installed mainly for aesthetic purposes and to protect a waterproofing membrane system. It is often unreinforced and could be thinner than the minimum 25-30 cm thickness but for current pumping and vibrating technical limitations.

The new philosophy is to make the primary support and lining meet the requirements for the permanent support and finish. This not only reduces costs significantly, but also reduces the civil construction period dramatically. "As a rough estimate, we believe the single shell approach could be 25-30% cheaper and up to 20% faster than the previous double lining techniques," said Mr Amberg. "To build these long base line tunnels within the available time and budget, a single shell lining is the only solution."

Single shell shotcrete linings in hard rock tunnels were first used in Switzerland in the late 1970s, and early 1980s, for military facility caverns designed to be shock proof using the more flexible primary support and lining of rockbolts, shotcrete and wire mesh.

However, the single shell proposal presents its own specific problems. The durability of primary support elements has to be guaranteed. The Gotthard base line tunnel is expected to be designed for a 100-year life without major repair. The short and long term performance of rock bolts remains a question for debate for many.

Another problem is water control. Concrete of any kind is not watertight. With a single shell of shotcrete, long term water control is more critical and many studies are on-going to develop more water-resistant mixes, additives to improve the impermeability of shotcrete, and methods of using plastic membrane waterproofing systems with shotcrete linings.

The back up of the Vereina Tunnel TBM has been specifically designed by ROWA to accommodate the application of the immediate and permanent support

Furka tunnel

Many primary concerns about the NEAT project arise from the experience of the 15km long single track Furka railway tunnel excavated by drill+blast beneath the Alps between 1976 and 1980. Although now an important link in Switzerland's national railway, the Furka Tunnel has become legendary for its catalogue of troubles and rising costs. The original 7 year construction period became a harrowing 9 years of despairingly difficult tunnelling and the unrealistically optimistic cost estimate of SF74 million in 1970 figures (excluding inflation and financing costs) rose to a final turnout cost in 1981 more than three times higher at SF225 million, or SF300.4 million with inflation.

Originally, some 90% of the 15km long tunnel was expected to pass through good quality rock with only minimal or no lining. In actuality, extremely difficult wet and unstable rock conditions were encountered under the maximum cover of 1,500m and 90% of the tunnel needed lining. Amberg AG was instrumental in reviewing the troubled project and estimating the cost of seeing it to completion.

With no lining expected in 90% of the tunnel, the cross section as already excavated was too narrow to accommodate an in-situ concrete lining. In-situ concrete would also be very time consuming and costly. A single shell system of rockbolts, wire mesh and shotcrete, with steel arches where necessary, was the only option. As such, a great deal of rapid research and development was required to meet the demands. Epoxy resins were developed for corrosion protection of steel rebar rockbolts, and corrosion-proof fibre glass reinforced bolts were introduced for the first time.

At the time, only dry mix shotcrete would meet the design specifications, and expensive ventilation systems were needed to keep dust within health and safety regulations. In preparation of the NEAT tunnels, the limitations of shotcrete technology are being studied in great detail.

For health reasons as well as technical advantages such as significantly less rebound and higher production capacity, wet mix shotcrete is preferable to dry mix. However, until two years ago, the only way to obtain good quality, high strength shotcrete of up to +30N/mm2 and more was with dry mix shotcrete. Wet mix was providing only 15-20N/mm2 strengths by comparison. But dry mix has a low performance capacity of about 5-6m3/h, too low for large scale projects.

The need to improve wet mix shotcreting technology and overcome the compromise on low early strength quality has seen shotcreting become a highly competitive and sophisticated sector of the tunnelling industry. A great deal of shotcrete research is taking place at the Hagerbach test gallery established near Sargans in Switzerland 25 years ago by Dr Rudolf Amberg (see yellow box). Tenants using the test tunnel, including Aliva, Sika, Sakret, MBT and others, have access to the facility's mechanical and laboratory equipment, its 15 strong permanent staff and its extensive services. Through recent development of shotcreting hardware and new chemical additives, it is possible to produce wet mix shotcrete of between 45-50N/mm² after 28 days with production capacities of between 12-16m³/h.

Vereina tunnel

Once laboratory tests confirmed these high quality results, Amberg used its authority as tunnel design engineer to change all shotcrete specifications from dry to wet mix on the Vereina tunnel project, another major railway tunnel project in Switzerland which is being considered as a testing ground ahead of the larger NEAT base line tasks. The 19km long single track Vereina tunnel, with the shorter Zugwald tunnel (2km), is being excavated by both drill+blast and TBM methods. An anticipated 6.5km of drill+blast is advancing from the south portal by a group led by Zschokke. On the north side, a group led by Stuag has assembled a 7.64m o.d. Wirth TBM to complete the short Zugwald tunnel before undertaking some 12.5km of the Vereina tunnel to junction with the drill+blast.

Like Furka before it, and the NEAT tunnels to come, the Vereina tunnel is designed with a single shell shotcrete lining. Rockbolting is systematic using between 6 and 15 glass fibre bolts/m which are fully bonded with single speed resin. The wet mix shotcrete specifies a early strength of 10N/mm² after 12 hours and a minimum strength of between 30-40N/mm² after 28 days.

Particular attention has gone into the design of the TBM's backup system manufactured by Rowa. Through collaboration between Ambergas the tunnel designer, Wirth the TBM manufacturer, Robert Walti the back-up system designer, and Stuag as the lead contractor, the TBM and its trailing gantries has been equipped especially to handle the installation of the immediate and permanent single shell lining. Rockbolts can be inserted from work stations at 5m or 50m from the face. Special erectors have been fitted to install steel arches immediately behind the cutter head and within 3m of the face if necessary. Shotcrete can be applied immediately behind the head also, but will usual take place from a 20m long working station between 40m and 60m behind the cutterhead. A special cleaning system has been incorporated to lift rebound off the invert and tip it onto the muck conveyor. A CIFA dense stream, pumped shotcreting system with a maximum 20m³/h capacity and a normal working capacity of about 12m³/h has been installed on the backup. Wet mix shotcrete will be transported from the near-portal hatching plant.

Waterproofing remains a problem when using a single shell lining. Much can be done to limit ingress by grouting up fissures using modern chemical grouts, and design of the shotcrete mix can improve water resistance. At Vereina, the wet mix specification requires that water must penetrate less than 20mm into the surface of a shotcrete sample when exposed to 1bar water pressure. Studies ongoing at Hagerbach are researching chemical waterproofing agents that can be either painted or sprayed on to the shotcrete or added into the mix to increase water resistance. In the meantime, the degree of waterproofing desired or required in a rail tunnel is also being discussed. As Mr Amberg explained: "Water ingress into a tunnel spans a wide spectrum, and complete water sealing with a full system waterproofing membrane may not be necessary. The need to control water ingress in the Gotthard Base Line Tunnel is principally because of its corrosive nature. This in turn is a function of the humidity in the air. Flowing water once channelled can be drained from the tunnel but high humidity has proven to be a serious problem in the Furka tunnel. A higher temperature of about 30°C with a lower humidity of about 60% is better for resisting corrosion that a lower temperature of about 25°C with a high 80-100% humidity.

Under the high 2,500m overburden in these long tunnels, the ambient temperature of the rock will rise to 40-45°C. During construction, a cooling system will be required to maintain the working environment at the face at the statutory 25°C. Once in operation, the piston effect of the trains will contribute up to 80% of the necessary ventilation. A ventilation system however will be required principally to deal with the event of a fire in the tunnel, but the system could also be designed to help control the air condition to reduce corrosion of fixed equipment. An important test being conducted at Hagerbach will monitor the performance of shotcrete against the hot rock surfaces.

Rows of shotcrete test panels line the floor of the Hagerbach Test Gallery awaiting their turn for detailed attention in the Gallery's geotechnical laboratory

Health and safety

The health and safety of the workers involved on these long tunnel projects is a major concern, particularly for SUVA, the national health and safety executive of Switzerland which also runs the country's industrial workers' compensation insurance scheme. With claims for compensation now running at record levels, particularly in Switzerland where compensation awards are generous, SUVA is anxious to control job related disabilities, particularly those that occur as progressive damage such as silicosis, the chronic fibrosis of the lungs caused by inhaling dust.

A meeting with Mr Hermann Egli, Director of Occupational Safety in the Civil Engineering sector of SUVA, explained concerns about shotcrete and its extensive use in the long, single shell tunnel projects. "The most dangerous particles in dust from shotcrete are the silicate in the sand which is less the 5µ in size. These cannot be seen in the air. They can only be monitored by instruments. The dust you can see in the air is not as dangerous since these particles are larger than 5µ and can be exhaled by the lungs. They do, however, damage the fine hairs of the respiratory tract adding to respiratory problems. The particles of 5µ or less cannot be exhaled and so accumulate in the lungs, causing fibrosis. "

"To control fibrosis, the content of silicate in the air (dust particles of less than 5µ) is limited by law for workers engaged in a potentially dusty environment for 8 hour shifts. Where silicate in the dust is between 0-1% the legal limit is 6mg of dust/ms of air. For 1-4% silicate, the limit is 4 mg of dust/ms and 0.15 mg/ms where silicate is more than 4% of the dust. If readings exceed these limits, the job is shut down until necessary steps are taken to rectify the situation."

"When using dry mix shotcrete where shotcreting continues for 2-3 hours in an 8 hour shift, it is not possible to meet the statutory restrictions. The wet mix technology has reduced the problem significantly and we have been working with various firms to improve wet mix performance further. Surprisingly, dense stream wet mix creates more dust than the thin stream wet mix as produced, for example, by the Aliva Duplo system. After several trials we found a reason why. As the dense stream mix is picked up, the high pressure air stream causes the mix to peel away from the larger aggregates and forces the fine particles of silicate into suspension. Introducing compressed air at the hopper and accelerating the mix along the full length of the hose overcomes this problem."

"In addition, additives can also help to limit dust. Sika's Sika-Tell 200, for example, is a reactive cohesion agent which could positively influence rebound and dust emission. "The best control of dust is adequate ventilation. In Switzerland, the law requires a minimum 1.5ms of fresh air/minute/man when working underground. This increases dramatically when working with dust or under the threat of natural gas. When working with diesel driven equipment, the legal requirement is 4ms/minute of fresh air for every 1kW of diesel power employed. However, there are technical limits to forced air ventilation systems as well as limits on the amount of money allocated to ventilation services. Limiting the creation of dust must go hand in had with developments in ventilation systems."

"Before any civil construction project starts in Switzerland, the contractor must submit a method statement to SUVA and have its ventilation and emergency evacuation procedures approved. At present my department has 35 inspectors to monitor health and safety requirements on all civil construction projects in Switzerland," said Mr Egli. "In 1993, two tunnelling jobs, one a roadheader operation and the other a TBM drive, were shut down due to air quality infringements. When the NEAT project starts, we will need another five inspectors to fulfil our policy of visiting each working site once a month. In the meantime, we are working closely with planners, designers and machinery manufacturers to ensure that health and safety concerns are addressed adequately."

Switzerland has a long tradition of advancing the art of tunnelling through the Alps. With the prospect of drawing on national and international expertise for the successful realisation of the NEAT scheme tunnels, Switzerland will help advance the science of large scale, hard rock tunnelling well into the next century.

Fig 2. The 50km twin tube St Gotthard base line tunnel will be excavated in 11 years using at least eight full face hard rock TBMs from two intermediate access points and the south portal with drill+blast or roadheader excavation from the bottom of the Sedrun access

Plan of attack for the St Gotthard tunnel

At least eight and possibly nine or ten TBMs of 8.9-9.1m diameter are expected to be used to excavate the two parallel tubes of the 57km long Gotthard base line tunnel for the NEAT project. At the northern end, an extra 14km of tunnel (2 x 7km on each tube) is added to initial proposals to pass the railway 200-300m inside the mountain and avoid the environmental opposition to having the line run through the valley at grade.

To achieve excavation within the 11 year construction period, the tunnel length is divided by three intermediate adits, the locations of which are determined by accessibility in the mountainous topography. The first is a 1.7km long horizontal adit about 7km from the north portal. The second is an 800m vertical shaft about 20km from the north portal. The third is a 2.6km 12˚ inclined adlt about 40km from the north portal or 17km from the south.

Tunnel excavation will be divided into three to five or more construction contracts, each with a 6-7 year construction period. These will start progressively, with the tunnelling beginning well in advance of surface works.

The most critical section in the Gotthard tunnel will be the middle 20km between the vertical shaft (Adit 2) and the inclined access (Adit 3). The shaft is expected to meet the tunnel alignment in the Tevetscher Zwischen Massiv (TZM), a series of sedimentary rocks which are expected to present difficult tunnelling conditions. After sinking the shaft, the tunnel tubes will be advanced north and south for a total of about 4km through this difficult zone using either drill+blast or roadheaders. Deformation of up to 50cm is expected in this area.

Elsewhere, two TBMs are expected to advance south from Adit 1 and progress about 12km toward the sedimentary rock but without entering into it. Another two TBMs will advance north from the decline (Adit 3) to meet the drill+blast or roadheader advance from the shaft.

Three TBMs are expected to work from the south portal. The first will be a 4.5-5m diameter pilot tunnel driven on the main tunnel drive. This pilot is needed to provide a haulage route to transport muck away from the TBMs advancing north from the declined adit since there are no muck disposal sites near the entrance. A large percentage of the spoil can be used for shotcrete aggregate. Two larger TBMs will then excavate the main tunnel tubes from the south portal breaking into the decline adits operation.

The short 7km section between the north portal and the first adit is not on the critical path and so both tubes could be completed by one TBM. The region around the north portal is a sensitive residential area and therefore it is expected to be unlikely that tunnelling will progress from the north portal. The TBM should therefore progress north from Adit 1 toward the portal.

Construction of the St Gotthard base line tunnel is programmed to commence in the second half of 1995 starting with the vertical shaft access. Regular cross passages will link the two running tunnels together for emergency evacuation for subsequent safe operation of the long rail tunnels.

SUVA is interested in seeing these cross passages installed at 500m intervals, but the discussions go on.

Fig 3. The 5km long tunnel is designed to investigate the presence and quality of a possible section of unstable sedimentary rock known as Piora mud

Tunnelling for geological investigation

The most difficult section of the St Gotthard tunnel is expected to be the passage through what is known as the Piora Mulde. This is a deposit of very granular sedimentary rock which looks and feels much like sugar. This rock is evident on the surface some 1,700 m above the tunnel alignment. Samples of the material have been taken back for testing and analysis at the Hagerbach laboratory. These reveal that the material is very poor with a low compressive strength and a high porosity of up to 40%.

The question is, does the Piora Mulde extend down to tunnel level, and if so, how wide is it? It is important to answer these questions as accurately as possible. If the deposit does extend to tunnel alignment, it will most probably have a high water content which could well be under the full 1,700m of hydrostatic pressure.

There is also the likelihood that this deposit is linked to other sedimentary rock deposits in the area, some of which have an influence on the foundation of large dams and reservoirs high in the mountains. To obtain more information about this zone, SBB, the client has authorised the excavation of a geological investigation tunnel. From the most suitable access point, a 5.2m diameter Wirth TBM has started driving a tunnel into the mountain toward the Piora Muldezone about 300m higher than the base tunnel alignment.

When, and if, the tunnel meets the sedimentary rock (a minimum advance of about 5km), the TBM will be withdrawn and a chamber will be excavated. From within the chamber, a series of core drills will be taken to confirm if the Piora Mulde does extend to tunnel level and if so, its quality and thickness.

If it is at tunnel alignment in significant quantity, a 300m shaft of 5.6m diameter will be sunk to the main tunnel level. From within this, a dewatering system will be established to lower the water head in the rock and grout injection will be carried out if considered necessary to stabilise the material in-situ. Several tests have been conducted at the Hagerbach to examine the quality of the Piora Mulde material and its ability to be stabilised with various injection materials and methods.

The SF40 million investigation contract was awarded in Summer 1993 to a Swiss joint venture of Mancini-Marti, Murer, Locher and Zschokke. The 5.2m diameter Wirth TBM started arriving on site in late 1993 and tunnelling started in January 1994. To early February 1994, the TBM had advanced some 200m and is progressing through good quality granite. Its most interesting work will begin when it reaches the expected interface with the zone of poorer sedimentary rock.

The information gathered from the investigation programme will be invaluable in preparing the methods needed to excavate the main tunnels through this difficult zone and mitigate the risk of extensive and expensive delays.

Where previously it was rockbolting systems which received concentrated research and development at Hagerbach, today it is the turn of shotcrete, particularly the wet mix techniques which were specified for use on the Vereina tunnel and will also be used on the long NEAT base line tunnel projects.

The Hagerbach test gallery facility

The Hagerbach test gallery near Sargans was started 25 years ago by Mr Amberg senior and the Swiss company SIG. The facility is one of few test galleries in Europe established as a dedicated test site. It is not an old disused mine, but rather provides the ability to perform tests in real tunnelling conditions.

The local Canton granted permission for the excavation of the gallery providing it remains purely a scientific laboratory. Amberg and SIG were the two original private promoters with a 60% and 40% shareholding respectively. All necessary funding for the operation of the gallery is collected as fees from those companies working in the facility as tenants. The gallery employs 15 permanent staff, owns a range of tunnelling equipment and operates a well equipped laboratory. There is a large blasting chamber able to withstand the shock and suck waves of blasts created by 50kg of TNT as well as a modern lecture room, well equipped dry rooms and bathrooms, and also a restaurant, all within the underground complex.

Mr Amberg senior, who spent much of his early career as the technical director of a large iron mine, was most enthusiastic to establish the test facility, realising that tunnelling would become a more important sector of the civil engineering industry in the future. When the mine closed in 1965, he turned to civil tunnelling. This then grew into the present Amberg consulting practice and other associated companies and interests including the Hagerbach facility.

The site at Sargans was selected particularly because it allowed exposure to two distinct types of rock. There is hard competent limestone of up to 250N/mm² in unconfined compressive strength and a deposit of softer dark shales of 40-50N/mm². The facility currently comprises a network of about 3.5-4km of tunnel. The extension of the network is not a priority, and advance only takes place if a new work area is needed or excavation techniques are being tested.

"The history of the facility illustrates the development of the industry," said Mr Felix Amberg. "Originally, it was drilling and blasting techniques which were being perfected. Then there was a period of intense rockbolting development including most recently, the glass fibre bolts. The glass fibre bolts of the Weidmann system were extensively tested in the gallery as were many of the new epoxy bonding resins. Epoxy resins have shown an unaltered state after 12 years in-situ when resin grouted bolts have been overcored and examined."

Today, there is a great deal of research in the field of shotcreting, both in developing new units and in perfecting new admixtures. Frequent core holes in the tunnel walls show the extraction of both rockbolt and shotcrete samples. Once applied, shotcrete is often blown off the walls to achieve a clean rock face for the next text. This is cheaper than excavating new headings.

During the recent visit to the gallery, a small heading was being heated to ambient temperatures likely to be encountered in the NEAT tunnels at depth to analyse the performance of wet mix shotcrete against hot rock.

The test gallery provides realistic conditions for the testing of new techniques without disturbing an actual job site and with the advantage of a fully equipped rock and materials testing laboratory on site for speedy and convenient analysis. In addition to providing facilities for the tenants, the laboratory also conducts quality control services for on-going projects. The facility has the ability to be involved in a project from the earliest geological studies, to establishing materials and design specifications, through to final quality control of the finished structure.

"The tests and results of individual tenants are confidential," said Felix Amberg, "but the gallery does create a forum for wider discussion about the type of developments now required to meet the challenges ahead. When new techniques are developed at Hagerbach, the Amberg consulting practice can write the technical parameters into the specifications for tunnelling projects on which it is engaged. This does not promote products by name, but ensures that new developments are introduced to the industry sooner than might otherwise be the case. Without compromising the confidentiality of tenants, the Hagerbach centre is open to sharing its research experiences and invites others to collaborate in the development of new and more effective solutions to problems faced by the tunnelling industry as a whole."