Planning the Metro
In planning the Metro, priority was given to completing the project rapidly and in an environment-friendly, financially favourable manner with as little inconvenience to the city as possible.
Before the actual construction work on the Metro could begin, it was necessary to relocate many utility supply lines.
A year before construction work started, Copenhagen City Museum undertook a series of archaeological surveys. During the excavations, traces of Copenhagen’s medieval fortifications were found. Copenhagen City Museum will also be following the construction work on the Metro during the rest of the construction period, so that archaeologists can intervene if anything of archaeological significance is found.
Important to prevent lowering of the groundwater table
Performing construction work twenty metres underground poses several problems. Avoiding harmful groundwater lowering is paramount, because a lowered water table could cause the surrounding buildings to settle. In some parts of Copenhagen, building foundations were made according to old piling methods using wooden piles that are under water.
A lowering of the water table would expose these foundations to air, and at worst they would disintegrate in a few years as the result of fungal attack. The construction method used in making the tunnel stations prevents harmful groundwater lowering from occurring. To monitor groundwater levels, a number of bore holes have been drilled along the entire Metro. The groundwater level in these holes is continuously checked.
Built from the top down
The tunnel stations are built from the top down. The basic procedure starts with the establishment of a watertight outer wall surrounding the station box. Next, the actual construction pit is excavated within the reinforcements. This ensures that the construction work occurs in a stable, dry pit that is impervious to water penetration.
Adjoining walls of concrete piles The outer walls of the station are concrete secant piles that are so tightly placed they form a cohesive watertight wall. The secant piling method was chosen because it is environmentally acceptable. Noise and vibrations are less than under conventional construction methods, such as sheet pile framing.