Articles & Researchs
23
IMIA WGP48, 2006 and Munich Re
on the tunnel's behavior during
as standalone or in a combined
Group, 2006. All the foregoing data
construction.
manner. From the work carried out
has been used in the work carried
by [5], it can be seen that most of
out by Konstantis, Konstantis and
Tunnel
Failures
vs.
Ground
the commonly used construction
Spyridis, 2016. Extensive reference
Conditions
methods exhibit failure events,
and use of that paper is made in
Tunnel failures can be manifested
including the most sophisticated
this contribution.
in many ways, most prominently
ones
(such
as
mechanized
as face instability and collapse. In
tunneling). Figure 4 below (as
Geology ­ Ground Conditions
the analysis carried out in [5], it was
extracted from [5]), provides an
The physical and mechanical
estimated that almost half of the
properties
of
the
geological
incurred failures can be attributed
Failure Types in relation to Ground
medium where the underground
to face instabilities. One fifth of
Conditions
structure will be constructed is of
the cases have been related
overview
of
tunnel
failures
utmost importance to the safety
to insufficient and inadequate
distribution in relation to the chosen
and integrity of the project. The
excavation support. These results
construction method.
behavior of the structure during
can be seen in Figure 2 below.
A
deeper
examination
of
the construction period and its
A further investigation into these
these failures has revealed the
interface with the surrounding
results also reveals the role of the
differentiating role of soil-like
ground are also very much
ground nature. The vast majority
ground conditions. Due to its
dependent upon the selected
of all failures, irrespective of failure
reduced physical, mechanical
construction
sequence
and
mode are related to the existence
and deformational characteristics,
methodology, in the degree
of soil-like conditions. This is
occurrences such as excessive
that these are stipulated in the
illustrated clearly in Figure 3 below.
deformations
and
excessive
design and realized during the
exerted stresses are more probable
constructionphase.However,there
Construction Methodology
are some ground characteristics
Each construction methodology
to occur, which in turn pave the
that could be considered a more
carries
its
own
specific
way for a failure event to happen.
"responsible" instigator for tunnel
characteristics
subsequently
failures than others.
affecting and altering the risk profile
It has been estimated (refer to [5])
of a tunneling project. Various
that almost two thirds of the tunnel
methods could be selected and
failures
happen
on
soil-like
used, subject to ground conditions,
conditions in contrast with rock-like
project
location,
previous
conditions, as it` can be shown in
experience
of
the
involved
Figure 1 below.
parties, plant and equipment
An exacerbating factor, especially
availability,
geometrical
in the case of fractured rock and
characteristics of the project, etc.
soft soils, is the underground water.
Indicatively, some construction
Variances in its level and pressure
methods are TBM, NATM, Drill &
can have a detrimental effect
Blast, etc, and can be adopted
Design
The success and progress of a
tunnelling project starts with the
design.
Adequacy and suitability of the
design provides the solid base
for a riskmitigated and successful
project.
Errors,
omissions
or
misinterpretation pose significant
threats to the project, jeopardizing
its safety and integrity. As per
Reiner, 2011, design errors comprise

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