Photo showing the world's longest road tunnel, the Lærdal tunnel,with a length of 24,509 metersconnecting Aurland to Lærdal, in Sogn and Fjordane County.
A tunneling rig in action in Norway.Recently, the focus has been on developing new and improved methods for mapping subsurface "problem zones" for the excavation of underground facilities.
There is a major focus on developing feasibility studies related to tunnel- and other underground constructions regarding the mapping of subsurface “problem zones”. The objective here is to prevent budget overruns and improve safety Much effort is focussed on improving feasibility studies prior to tunnel excavation. Photo from the new highway E39 between Trondheim and Orkanger, Sør-Trøndelag County. during construction.
NGU is cooperating with the Norwegian railways and roads departments in many tunnel projects.
NGU has several relevant datasets for feasibility studies for the construction of tunnels. In addition, NGU specializes in several alternative techniques that may be used in feasibility studies, and is therefore involved in developing improved methods for feasibility studies.
NGU has been involved in several tunnel projects, the largest and most extensive are briefly described below:
A multi-partner co-operative project during 2000-2003, financed by the Norwegian Road department (Vegdirektoratet), Norwegian Railway department (Jernbaneverket) and the Norwegian Research Council (Norges Forskningsråd).
NGU managed the sub-project “Feasibility studies”, documenting that new techniques can identify and characterize “problem zones” in the subsurface, and that these techniques are better and more economical compared with more traditional techniques. With such new techniques, locating and identifying “problem zones” may be easier and reduce costs while increase safety during tunnel construction. NGU has contributed to developing these “new” methods.
Rogfast is a planned sub-sea tunnel beneath the Bokna fjord in Rogaland County, from Harestad at Randaberg (Stavanger) to Arsvågen at Western Bokn (island). About halfway in the tunnel, a 2 km long arm is planned up to the island Kvitsøy, giving this island a connection to the main land, in addition to contributing to ventilation of the tunnel. Rogfast will replace the existing ferry connection between Mekjarvik-Kvitsøy and Mortavika-Arsvågen, where capacity constraint has been an issue during rush hours. This tunnel project will make the Bokna fjord ferry-free.
Related to this project and other tunnel projects in the area, extensive seismic surveys have been conducted. In addition, NGU has conducted air borne magnetometry measurements, and carried out a digital structural analysis of the entire Bokna fjord area.
Mapping of deep weathering
NGU had a priority program in the greater Oslo area (GEOS project) during 2002-2007. Within this program a method was developed to detect zones characterized by deep weathering. This deep tropical-type weathering occurred during the Triassic to Jurassic Period (more than 150 million years ago), when Norway was located further south under sub-tropical conditions (about 30oN). As part of the study so-called awareness maps were developed showing potential “problem zones” containing deep weathering in the Oslo region. Such knowledge is especially important when constructing tunnels and other underground facilities in the area.
Tunnels and groundwater leakage
Water can be both a pleasure and a plague. It is good to know the bedrock's water yield when drilling a well for groundwater or constructing a tunnel. Water leakage in tunnels increases the budget cost, due to extra cement injection, and increases the risk of unstable rocks. NGU's groundwater database provides information about groundwater in bedrock, and contains a national database for all water supply and energy wells in Norway.
The mapping of zones of structural weakness, such as faults and fractures, is important for registering specific properties that help to predict the extent, direction and width of these zones. Fault and fractures increase the permeability of the bedrock, and therefore increase the risk of water leakage and instability in tunnels, or, alternatively, increase the water yield of a well.
Äspö underground laboratory, SKB, Oskarshamn, Sweden. An example of an existing underground facility, used as a laboratory (www.skb.se). Underground facilities include parking garages, sports halls and storage/disposal sites.
of nuclear waste (SKB):
NGU participates in mapping bedrock properties at two potential underground waste deposit sites in Sweden, Forsmark and Oskarshamn (www.skb.se ). Sweden has two operating nuclear power stations and has therefore a need for safe disposal of nuclear waste.
NGU's contribution includes mapping zones of structural weakness, such as faults and fractures, based on field studies and core logging. Knowing the properties of such zones helps to predict the extent, direction and width of these zones.
Faults and fractures increase the permeability of the bedrock, which is critical with respect to potential mobilization of radioactivity. The mapping project was completed in 2007, and a political decision on which site is most suitable is expected by 2009.