Civil Engineering Reference
In-Depth Information
23.3.7 Recommendations for the Construction of Tunnels in Swelling Rock
The lesson learnt from this case history is that a safe and economic construction of a
tunnel located in unleached Gypsum Keuper, well below the anhydrite surface, is pos-
sible if water contact with the excavated rock surface is avoided during construction.
Provided that the unsupported tunnel is stable, as can be expected, this can be accom-
plished by means of
- smooth excavation to avoid loosening of the rock mass (e.g. smooth blasting, excava-
tion by means of a road header or a combination of both),
- air flushing of blast holes,
- dust prevention measures,
- sealing of rock surfaces immediately after excavation by a thin shotcrete membrane
to minimize loosening and to protect rock from air humidity,
- sealing of the temporary face with shotcrete in case of shutdowns.
Under no circumstances should water be used for dust control. Also, rock bolts should
not be installed in order not to create paths for seepage water.
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