Actes du colloque - Volume 2 - page 795

1677
Technical Committee 204 /
Comité technique 204
4 TUNNEL MAINTENANCE AND INSTRUMENTATION
Three papers were assigned to this topic. The first paper
presents the general concept of inspection routines on
underground structures. The other two papers are about specific
instruments for monitoring tunnels.
In their paper “Engineering inspection and supervision of
tunnels and underground stations of urban metro systems”,
Katzenbach and Leppla
describe the negative effects of the
lack a proper regulation for inspection of underground
constructions. Both the general stability of the structure and the
life cycle costs are jeopardized without a proper inspection
routine. A concept with four different categories of inspection
was developed and applied to the Frankfurt am Main metro
system. Definitions of insufficiency and defect were stated and
put together to generate a grade for the underground
construction at the end of each inspection. The experience
shows that the defined modalities and continuous procedures
guarantee a sustainable preservation of the underground
structures by early identification of insufficiencies and defects.
Figure 11 presents an example of what was classified as the
main inspection of a tunnel.
Figure 11. One of the procedures for a main tunnel inspection (after
Katzenbach and Leppla).
Huang
et al.
present another study of the Taipei Mass Rapid
Transit (MRT) in their paper “Field monitoring of shield tunnel
lining using optical fiber Bragg grating based sensors”. A strain
monitoring instrumentation system was employed to confirm
semi-empirical designs and to monitor especially problematic
zones of the tunnel. Optical fibre was used to assess the strain
evolutions from the start of the concrete pouring of the segment
and to obtain results without disturbance by electromagnetic
interference.
The optical fibre Bragg gratings (FBG) were installed in the
centre of the reinforcement bars (Figure 12) and the readings
were recorded from pre-cast concrete section production until
installation and operation. The continuous readings enable the
analysis of the lining reaction to each construction phase. The
record also showed a strain fluctuation during the tunnel
operation that was associated with variations in the internal
temperature of the tunnel.
Figure 12. Placement of optical fiber in the reinforcement bar (after
Huang
et al.
).
Gay
et al.
present a part of a project to evaluate the
constructability and safety of cell preparation tunnels for
radioactive waste storage on Callovian-Oxfordian clays, in their
paper “Monitoring and Instrumentation of demonstrators
storage cells (CMHM)”. A set of innovative instruments were
designed to monitor these 40 m long, 0.7 m diameter prototype
tunnels. The devices enabled video footage associated with a
geo-referenced trajectory and optical zoom to detect cracks of
one tenth of a millimetre. Measurements of convergence,
temperature and relative humidity of the tunnel were also
recorded.
The metallic liner was also instrumented to obtain local and
distributed strains, temperature and relative humidity. For that a
series of laboratory tests was conducted to control the behaviour
of different optical fibres under mechanical and thermal
variations. Experiments are underway to simulate the presence
of waste CMHM packages, by thermally loading the tunnels to
90 °C. The results obtained until now show a great performance
of the instruments and could detect intriguing behaviours as
anisotropic convergence of the tunnels. A schematic drawing
and a picture of the convergence measurement device are on
Figures 13 and 14.
Figure 13. Overview of the device to measure the tunnel convergence
(after Gay
et al.
).
Figure 14. Picture of the device, inside the tunnel, to measure the tunnel
convergence (after Gay
et al.
).
The papers in this section present important messages for the
session. It is important that we enhance our design concept of
underground constructions beyond construction and early
operation. Accounting for the life cycle and associated costs of
the underground space, we can ensure technical and financial
feasibility of the whole service life of the structure. The paper
from
Katzenbach and Leppla
present a sight to that matter.
Huang
et al.
and
Gay
et al.
remind us that is always possible
to confirm design predictions for empirical designs and special
tunnel conditions by measurements. Most important it shows
how important it is to properly describe how field
measurements are obtained, which instruments were used and
how, so that the instrument’s associated shortcomings and
advantages are accounted for in the data analysis.
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