As far as the single underground work (cavern or tunnel) is consIdered - instead of the whole structure that can have one of more tunnels - the physical features of the environmental impact are examined, why the social and economical aspects are not taken into account. Actually, an underground work gives some positive points environmentally friendly, in a way more incisive than other structures built on the territory; these key points are interesting to choose the underground solution:
the underground structure does not create physical barriers crossing the land; It is not exposed to the site, and only the two adits are visible; the operation is not influenced by atmospherical agents; it is not subjected to surface stability phenomena (apart those of the portals); less maintenance costs are required if compared to an analogous surface structure; the tunnel reduces the length of the way offering the conditions for energetic savings; (during the operation) the emission of noise, gas, dust are concentrated at the adits '
it is quite protected against the seismic actions. 1 he underground work presents also negative environmental features. which can decrease the level of acceptance.
Apart from the disturbs due to the construction phase when the land is occupied by operative services (roads. houses, trucks) - which are nevertheless reduced when compared to the open site works - one can have the noise dust gas vibration emissions, pollution Water, perturbation of' normal load traffic and surface uses, especially when located in urban areas; underground construction have also four other main environmental problems:
perturbation, pollution and drainage of the groundwater; selliements of the surface of the land; Waste rock disposal: uncertainties in the preventive definition (for example in the design phase) of the geological, geotechnical. geohydrological conditions of the underground, which determine the risk of collapse and consequently sink holes. On the other site the risk of delays and increasing of the construction costs: I These demanding 'subjects have been studied by the ITA (Internalional Tunnelling Associations) which created in 1995 the Working Group 15 under the name of "Underground works and environment". The main objective of this group is 10 help the economic agents that operate in the underground world to take advantage of the opportunities and to minimiqe the risks associated with the new environmental culture.
Environmental legislation has both positive and negative consequences on the different agents that operate in the underground world. But on the other hand, an increase in production costs and a major responsibility demand of the economical agents. As environmental legislation becomes more and more strict. underground works will take advantage of their advanced positionas compared to the superficial ones. The tunnelling associations of the countries participating in the survey hold varying opinions about the interrelations between underground works and the environment, although the totality consider that the increasing environmental sensitivity and legislation will have a positive influence on the future development of underground works.
