Hidden Aspects of Urban Planning : Utilisation of Underground Space

Maximising space in our urban towns and cities remains one of the great challenges of the future. As the need to protect existing green areas grows amid ever increasing demands for more homes and work places, mass transit systems and modern infrastructure, so new approaches must be found to better utilise space available. Improved use of underground space offers new and exciting opportunities for landowners, planners and developers, bringing many hidden benefits. However, underground development is not without its risks. This paper highlights some of the work of COST C7 Working Group D contained in their publication “Hidden Aspects of Urban Planning, Surface and Underground Development”. It describes some of the benefits and risks associated with underground construction, methods in which planning and control of underground space can coordinate and the potential in underground thermal energy storage. The key principles involved in underground construction are illustrated with examples of best practice from around the world. Figure 1. The underground entrance to the Louvre This paper summarises a few sections of the publication as a reminder that ground is not just a challenge, but a valuable resource that should be celebrated and protected. 2 BENEFITS AND CHALLENGES OF UTILISING UNDERGROUND SPACE The demands for space have resulted in cities that have spiralled upwards with towers and skyscrapers cluttering the skyline. However, while building upwards, we should not forget the resource that lies beneath our feet. Utilising underground space remains one of the great challenges for the future. The potential is to bury unsightly car parks, highways and shopping malls, and direct the surface space that this unlocks to other uses that improve the urban environment. The benefits of utilising underground space can be summarised as follows. Efficient land use and improvement of the environment: realising the potential of underground space in congested urban areas and releasing surface space for other uses such as parks and recreational areas. Construction of road tunnels relieves surface routes for cyclists, pedestrians, emergency vehicles and public transport. Aesthetic: removing unattractive structures such as car parks, roads and shopping malls from the horizon. Sustainable development: removing the need for external cladding and finishes leading to efficient use of materials and cost savings. Conservation of energy: using the ground’s natural insulating properties to absorb noise and energy, allowing more efficient heating or cooling systems or harnessing the ground for energy storage. Protection of people to extreme weather conditions. Security: e.g. bank vaults and bomb shelters. Ground works are often perceived as one of the highrisk areas of development and underground construction is not cheap. However, a study by the UK’s Automobile Association (2001) showed that through new technologies the cost of tunnel construction has been falling by around 4% each year. The cost of urban tunnels in the UK starts at around £50 (€80) million per kilometre and can be cheaper than surface building where acquiring land and moving utilities is expensive. The cost of tunnelling in other countries can be cheaper, particularly where there are good rock conditions and previous tunnelling experience. For example, rock tunnels for the Helsinki Metro were around €10 million per kilometre to construct (Vähäaho, 1999). Savings can also be made in other areas such as a reduction in need for external building cladding. Cladding and finishes typically account for about 15% of a building’s cost and providing a watertight exterior is usually one of the key milestones in the construction programme, on which many other activities rely. Typical curtain-walling costs in London range between £250 to £500 per square metre (€420 to €840). As a typical example, a recent contract for a two storey building was let at £0.9 million out of a total project cost of £5.7 million. The market in cladding is volatile and often over-heated, with demand outstripping the supply capacity of reputable subcontractors. This poses challenges for the procurement and design team, often leading to issues over quality and performance of the product, and the stability of the subcontractors in question. In comparison, building underground entails retaining structures where the costs and performance are more predictable. The potentials in underground development are best illustrated through the successful international examples that follow. Preserving historic areas: The Louvre, Paris, France The new entrance hall to the Louvre is a buried structure built in the courtyard of the historic Louvre Palace. The glass pyramids designed by IM Pei are the only sign above ground of the hall and new galleries, and provide an eye-catching entrance point and natural light to the space below. Locating the entrance hall below ground removed a large potential intrusion from the courtyard and allowed the designers freedom in choosing the best shape and layout for the hall (Figure 1). Figure 2. Viikinmaki waste water treatment works, above and below ground Underground cities, protection from the climate: Montreal, Canada Montreal has the world’s largest underground city containing 31km of passageways, 10 metro stations, a railway station, bus terminal, more than 1600 shops, 200 restaurants, 40 banks and 30 cinemas as well as hotels, offices swimming pools and theatres. Begun in the 1960’s, apparently based on an idea of Leonardo de Vinci’s, the “city under the city” grew as developers realised the importance of linking into the underground network and the metro system. The subterranean world protects citizens from the snow, rain, wind and heat, providing a climate that is “eternally spring” and an environment that is free from traffic and road-related accidents. Financing underground infrastructure through surface housing: Hong Kong In Hong Kong, underground metro stations are constructed with high density housing and shopping developments above them. The market value of space is such that these developments can offset the cost of metro construction. Underground industrial plants, protecting the environment: Helsinki, Finland Helsinki’s Viikinmaki waste water treatment plant is one of the largest underground spaces in the world, processing all of Helsinki’s waste water (Figure 2). Locating the treatment plant below ground and providing housing and leafy park areas overhead, was considered the only way to obtaining planning approval for such a large industrial plant. Burying this structure also reduces gas emissions and noise pollution and allowed the owners to expand the plant with minimum disruption to the community. The housing estate covers an area of 60 hectares providing accommodation for 3500 people. Improving mobility, the environment and economic growth: The ‘Big Dig’, Boston, USA Boston’s ‘Big Dig’ is the most ambitious tunnelling project in the world running at US$12.2 billion (€13.9 billion). Currently, six lanes of elevated highway run through the city centre carrying 190,000 vehicles a day. Congestion costs US$500 million (€570 million) a year and accidents are four times the average for an urban interstate highway. The new tunnels will free up traffic, create more than 150 acres of new parks and open up new spaces. Carbon monoxide levels are forecast to drop by 12% across the city. Innovative road tunnels: Versailles, Paris, France The final section of the A86 ring road around Paris is being completed near Versailles. Costs are radically reduced by building the tunnel for light vehicles only. Reduced ceiling heights (2.44m) enable two road decks, each with two lanes and a hard shoulder, to fit within a single 10.4m diameter tunnel. The project, involves nearly €1.6 billion and is being privately funded with toll collection in place when operational. Tunnel boring machines are being used to excavate the soil and with 90% of the construction underground, noise and vibration disturbance at the surface are imperceptible. Secure storage: National Archives of Sweden The National Archives of Sweden are housed in a six storey rock cavern with shelving space in the order of 80,000m. The collection ranges from Medieval documents to modern computer records. Storm-water storage to prevent flooding: The Snake tunnel, Stockholm, Sweden “The Snake” tunnel beneath centre of Stockholm is 3.7 km in length with a total volume of 35 000 m. Its purpose is to store storm waters at times of heavy rainfall, preventing the attenuation of water run-off