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The Worlds Largest Cavern Hall For Public UseGjovik olympic hall Gjøvik is situated on the shore of Norway’s largest lake, Mjøsa, and it is the largest in-land city in Norway with 27 000 inhabitants. When Lillehammer was to be host for the XVII Olympic Winter Games in 1994 it was decided to place some of the arenas in neighbouring cities, one of which is Gjøvik.

The municipality of Gjøvik immediately seized the opportunity. They responded to the challenge by employing state-of-the-art techniques to construct a hall tailored for participant and spectator fulfilment. The hall was to be a multi-purpose arena useable for instance for ice hockey, figure skating, curling, track & field, and swimming as well as for conferences, exhibitions and fairs, though not all at once, and with a capacity for 5000 sports-spectators. And one thing more, such a structure would normally have dwarfed the surrounding buildings in a relatively small city like Gjøvik, so they decided to build the whole Olympic Hall as a subterraneous hall, in solid bedrock. The hall was built inside the Hovdetoppen mountain right in the centre of Gjøvik. The first drawings was made in 1989. The Contractor was Fortifikasjon A/S and the owner is the Municipality of Gjøvik.

Technical Specifications:

Dim.
Height : 25 m
Length: 91 m
Width: 61 m
Seating Capacity: 5,100
Net Area: 10,010 m2
Gross Area: 14,910m2
(including walkways etc.)
Stadium: 1,965 m2
Public Areas: 2,224 m2
Media Centre: 2,110 m2
Participant Facilities: 263 m2
Admin. & VIP Centre: 577 m2
Operations/Maintenance: 515 m2
Technical & Electrical: 638 m2
Additional Facilities & Storage: 1,100 m2
Total Cost: 135 million NOK.

The Idea
Norway is a mountainous country, with more than 50% of the land surface consisting of exposed rock. That is why the tradition of building underground constructions is deep-rooted. Just look at the more than 200 underground hydro electric power plants, or the more than 700 road tunnels. Norway has a number of underground sports halls and swimming pools, which double as air-raid shelters in case of war. The Municipality of Gjøvik was in fact one of the first in Norway to build a underground swimming pool (completed in 1974). So when Gjøvik was chosen as one of the locations for an Olympic arena it was only natural to consider building an underground ice rink. The idea was undoubtedly not brand new, but one episode is worth mentioning: The aforementioned swimming pool was designed by a firm of consultant engineers in Oslo. One day in the late autumn of 1989, Jan A. Rygh, an engineer and Technical Manager in the firm, and Municipality Engineer in Gjøvik, Helge Simenstad, had inspected some of the work the consultant company had carried out on the underground swimming pool. In the evening they shared dinner at one of Gjøvik’s hotels. During the meal, Simenstad revealed that Gjøvik was to host part of the upcoming Olympics with an ice rink arena. Rygh later said it felt like he had been struck by lightning. For several years he had longed to build a huge underground sports hall, and he was convinced that this was technically feasible. In answer to Simenstad’s news he exclaimed: “Let’s build a cavern in the mountain! What do you think?” The two engineers stayed at the table for along time that evening, drawing the first sketches for the Olympic Hall on a piece of napkin. It was the humble beginning for a long and tedious process. The municipality of Gjøvik was therefore faced with a difficult decision: whether to build an underground, or an outdoor ice arena. Naturally there were arguments going both for and against these alternatives, but on January 24. 1991, after thorough investigations, the local council reached it’s decision: “We’ll build and underground arena!” Thus the idea, which originated from sketches on a piece of napkin was to be realized.

Gjøvik municipality employed the finest experts and engineers to proceed with the planning of the project. A project which gained interest from both the Norwegian and foreign engineering community. Experts throughout the country, researchers, consultant engineers and architects, was involved in this first critical phase. Problems and questions arose, but by pulling together solutions were found, and answers come up with. The total project was led by the consultant engineering firm Fortifikasjon A/S.

The Rock
The rock is a gneiss, perhaps as old as 800 to 1100 million years old.
This rock type is quite suited for the constructing of caverns, but naturally a thorough pre-investigation was preformed before construction started. A very extensive geological investigation was begun, drilling for core samples to be tested in laboratories at SINTEF and NGI. In-situ tension in the rock mass was measured as well as many other geophysical test. Computer models of the cavern hall was made, so one could make predictions about how the rock mass in the vicinity of the planned cavern would react to the drilling and blasting.

The Norwegian-developed Q-method also came into play. This is an advanced method of judging rock mass quality, and proved invaluable in determining the need of rock support during the construction. A detailed model of the rock mass and the effects the excavation of the cavern would have on these was also preformed, later it was proved that the rocks actual behaviour and movement came within neglecting distance from these calculations.

Under the construction, a running surveillance of movement in the rock mass above the cavern was preformed. and the crown of the roof was measured to have settled about 8-10 mm, which was expected based on the model and calculations preformed in the pilot studies. This surveillance was done both via a number of pressure sensors in the roof of the cavern and by meticulous height measuring of the terrain surface on top of the hall.

Research
The research programme “Underground public arenas was an integrated part of the planning, construction and start-up process of the Gjøvik Olympic Mountain Hall. Without this programme the project would probably never been possible. The research was led by a control committee, consisting of representatives from all the participating companies, and was carried out by Norway’s leading research institutes. The programme was divided into four main areas, namely:
-Ventilation, energy, fire and safety.
-The environment, safety and documentation.
-Rock mechanics and engineering geology.
-Laws and regulations.
The programme also included the international marketing of Norwegian underground technology in general, and the publication of research results linked to the Olympic Hall in particular. The results from the project was continuously passed on to, and used by, the contractors during the construction phase.

The Blasting.
The blasting of the cavern required more than one point of attack to get the masses out fairly rationally. The first tunnel was situated about 10 meters below the roof level of the cavern-to-be. The blasting was done in sections along the hall, with securing work done along the way. In total 170 tons of dynamite was used in the blasting process. The vibrations made by the blasting was monitored continuously. In the beginning the rock masses was brought out via a transport tunnel which begun near the entrance of Brusveen Gaard in Hans Mustadsgate (southerly direction.)
This tunnel entered the main cavern hall approximately 10 meters below the planned roofline of the cavern. The roof area was then blasted free, one section of the time, and each section thoroughly secured by bolting before the next was begun. Only when the whole roof area was blasted free, and bolted, did the work downwards begin. The majority of blasted rock was brought out through the main entrance tunnel in Røverdalen. This blasted rock material was seen as an asset, not as a problem, and for instance was 100.000 m3 rock mass used to make a promenade and a park area alongside the lake Mjøsa.

The amount of explosives and the distribution of detonators were arranged with the normal criteria for shock waves in surrounding buildings and installations. Telenor’s installations in existing underground installations were assessed for acceptable shock wave levels from the blasting. All this meant that the surrounding settlements were exposed to shock waves in less degree than what would normally have been the case. The shock waves was measured continually, and all homes and buildings near by were studied in detail before work began. This to ensure that any specially vulnerable constructions could be shielded from the worst of the shock waves.

Architecture
The room layout of the 9 stories high hall is large and complex, having to accomplish a number of special requirements from the athletes, the media and VIP’s. It was also of great importance to make this Olympic Hall into an exciting and different architectural experience. The Olympic venues were after all designed to reflect Norwegian culture and character. The huge hall deep inside the mountain brings thoughts of the Hall of The Mountain King in “Peer Gynt” and the caves of the fairy-tale trolls with their gleaming hoards of treasure. The intention has been to play on this effect, for instance is the shotcrete used on the walls and ceiling deliberately dark and mysterious. The lighting allow deep contrasts, from the entrance tunnel which is dark with pools of concentrated light, to the magnificently lighted hall itself, which emphasises the enormous dimensions. The dark entrance cavern also allows the eyes of the spectators to adjust, so the main hall seems brighter lit than it actually is. The contrast between the dark and rough finish of the rock itself and the slender and delicate lines of the grand stand is also used deliberately, a contrast between nature and technology so to speak. The architects have strived to make a harmonious, classical amphitheatre, providing close contact between the spectators and the players. The choice of materials and colours was also influenced by the rock. A magnificent red rock, visible in few places in the hall, prompted the choice of red as the main colour in the hall, from bright and clear, to a deep, deep hue. The use of glass tiles is intended to give associations to ice. The shine metal used in the installations and energy saving equipment in the ceiling on the other hand represent veins of silver embedded in the rock. Architect Steinar Moe of architects Moe Levorsen A/S was responsible for this concept.

Safety
Safety naturally had a high priority in the design of the hall. Norway’s foremost experts on safety was involved and they collaborated with Statens Bygningstekniske etat, (National Office of Building Technology and Administration), in the procurement of safety specifications in the case of fire, to reduce and prevent personal injury. These specifications include descriptions of inflammable or fire-retardant materials to be used, fire sections, fire escape routes (fire ventilation) and the capacity of entrances and fire escapes, which are tailored to the number of spectators.

All specifications were included in the plans. An underground safety area, surrounding the spectators stands, has also been built, bringing in a new aspect to this concept. Should a fire break out in the spectator stands or in the arena, evacuation will take place to this safety area, where it is safe to remain until further notice is given on the PA system. The facilities are protected against the effects of nuclear and conventional weapons as well as poisonous gases, in accordance with the regulations of the Civil Defence.

The Opening, and subsequent use
The opening took place on Thursday 6. May 1993 and was celebrated by a huge show, televised on national television, and with over 5000 guests in the hall itself. The true test came with the Winter Olympics in February of 1994. During the Games, the cavern was the venue for 16 ice-hockey matches, including two quarter-finals and a semi-final. The cavern received a great deal of praise and carried off its baptism of fire with style and elegance. The municipality aimed for a increase in its long-term competitiveness by way of the Olympics. The status of the arena doubtlessly has helped in achieving this aim. The hall has also showed it’s true potential in the time that has passed since the Olympic Games, it is a multi-purpose cavern, offering opportunities for a long range of sporting and cultural events. It has been the host of venues such as exhibitions, trade fairs, festivals and conferences, as well as sporting events. The cavern can cater for events of a size and volume previously impossible in the area. And it’s own restaurant at the Mountain garden links the hall to the swimming pool and makes for an interesting scene for a dinner.