Gotthard base tunnel rock burst phenomena in a fault zone ...

stations in the MFS. No triggering of a micro tremor
could be identified. Based on above mentioned
aspects the case of a stress drop near a tunnel in the
MFS Faido has been accepted as a residual risk.
Since a residual risk cannot be completely excluded,
the owner of the tunnel, ATG decided to install
seismic measuring equipments and vibration sensors
in the linings of the tunnels in the MFS Faido for a
permanent seismic monitoring during operation.
6. CONCLUSIONS
During tunneling at great depth in geological
conditions as encountered in the MFS Faido micro
tremors triggering rock bursts are likely to occur.
The stress redistribution due to tunneling and
the stress concentration in hard rock in combination
with an existing zone of weakness (fault) favors the
occurrence of micro tremors.
The micro tremors did clearly correlate with the
excavation activities. After terminating the excavation
no more micro tremors have been identified.
Micro tremors cannot be avoided. During
construction precaution measures such as closing of
critical sections and flexible support consisting of
flexible rock bolts and steel arches are to be applied.
A seismic wave is deviated by a weak zone.
With the orientation of the weak zones in the MFS
Faido a seismic wave is deviated towards the tunnels.
The dynamic impact on a lining of a tunnel in front of
a weak zone and exposed to a more or less unhindered
micro tremor’s wave is considerably higher compared to the
impact on a liner of a tunnel in the ‘shelter’ of a weak zone.
The specification of the design micro tremor
for the MFS Faido is conservative.
Excluding the additional loading due to a
spontaneous ‘stress drop’ in the direct vicinity of a
tunnel there has been no need for improving
(thickness, additional reinforcing) the linings
designed for the static load case in the MFS Faido.
ACKNOWLEDGEMENT
The authors thank the AlpTransit Gotthard for the
permission to publish the paper.
REFERENCES
1. Hagedorn, H., Rehbock-Sander, M., Flury,
S.,Gotthard Base Tunnel: State of the works and
Special Aspects, Proc. Int. Symposium on
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2.
Construction and Operation of Long Tunnels,
Taipei, Taiwan, 7. - 10.11.2005
Rehbock-Sander, M., Rock Bursts Experience
gained in Mines and Deep Tunnels, Proc. 4 th Asian
Rock Mechanics Symposium (ARMS 2006),
Singapore, 8.-10.11.2006
3. ITASCA, UDEC – Manual, Theory and
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Heuze, F.E., Morris, J.P., Insights into ground shock in
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6. Harris, C.M., Crede, E.C., Shock and Vibration
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BIOGRAPHICAL DETAILS OF THE AUTHORS
Heinz Hagedorn completed his study
in civil engineering at the Swiss
Federal Institute of Technology (ETH)
with a M.Sc. degree in 1969. From
1970 to 1979 he was working at ETH
with the rock mechanics institute of
Prof. K. Kovari. The activity consisted
in developing a Finite Element
program designed for underground
structures and research activity in material testing and
field measurement. Since 1979 he has been working with
Amberg Engineering Ltd., Switzerland as a geotechnical
expert. For numerous large underground constructions
such as tunnels, caverns etc. in Switzerland and abroad he
provided geotechnical expertise and consulting for design
and during construction.
Rolf Stadelmann obtained his M. Sc in
Civil Engineering from the ETH
Zurich, Switzerland in 1992. He
specializes in general stability
analyses, temporary & permanent
excavation support systems, as well as
in structural design of all types of
tunnel lining. His core competence is
also in the quality management for
geotechnical analyses as well as in the development of
Contractor’s alternatives. He has in-depth experiences in
underground space design for all kinds of rock conditions.
Since 2003 he is Head of Geotechnical Department of
Amberg Engineering Ltd in Switzerland.