Geoscience Reference
In-Depth Information
Figure 15.1b A directional drilling is completed
Tunnels under waterways were originally constructed in open excavations
reaching a depth of 25 m. The required groundwater drainage caused significant
damage in the surroundings (settlements, desiccation) and the method was
abandoned. The immersion method (Fig 15.2), applying prefabricated caissons,
which were floated to their location, was successfully used and further improved.
In urban areas the cut-and-cover method, applying watertight screens (diaphragm
walls) and a 'roof' on which the daily life continues, is used, but disturbance to
traffic and living, and damage induced by partial groundwater drainage, even with
a recharge system, is always there, usually reaching an additional 10% or much
more in unexpected situations, above the planned construction cost.
open excavation
immersion
TBM
cut and cover
tunnel boring
Figure 15.2 Tunnel techniques
During recent decennia shield-boring machines have come in use to construct
underground tunnels with less disturbance at the surface. Here, the challenge is to
keep the tunnelling process stable and efficient in the soft and variable soil with
high water levels. At present, about 30 of these complex transportation crossings
have been constructed in the Netherlands, with a length varying from 300 to 6500
m, the longest reaching a depth of 60 m, and they function well.
Search WWH ::




Custom Search