Articles & Researchs
24
properties is usually significant and
catastrophic events could occur
following a failure. Shallow tunnels
are also prone to the creation of a
"chimney-like" failure mode, which
in turn could have unprecedented
consequences on the adjacent
and overlying structures, including
both underground (i.e. utilities)
and at grade (i.e. buildings).
From the analysis carried out by
[5] on the existing tunnel failures,
it is concluded that the majority of
them are demonstrating relatively
40% of the causes of underground
provides
information
in
the
low
overburden
which
vary
failures.
direction of validating the initial
from 2m up to 30m. This can be
As per the work carried out by
design assumptions and facilitates
illustrated in the following Figure 5.
[5], direct design errors (such as
further improvements and value
The cross-sectional area of the
those related to tunnel support
engineering activities.
tunnel
excavation
is
directly
dimensioning requirements) count
related to the development of the
for almost 30% of the examined
Tunnel Geometrical Characteristics
surrounding ground deformations.
cases. An increased level of safety
The distinct characteristics of each
The
volume
loss
determines
can be achieved through design
tunnel individually, play an explicit
the magnitude of the surface
optimization
and
value
role in the actual failure mode and
settlements and the extent of the
engineering with due care taken
type. These characteristics could
generated
settlement
trough.
on
satisfying
constructability,
include, but not Tunnel Failures vs.
The assessment of the size of the
safety, serviceability and meeting
Construction Method limited to,
failed tunnels (as included in the
all contractual requirements.
the size of the excavated area
work carried out by [5]) reveals
A particular area of interest
(cross-sectional area), the depth
that the majority of them feature a
with significant merits, yet in
of the tunnel axis (i.e. the height of
diameter ranging from 6m to 12m.
many
instances
undervalued,
the overburden ground cover), the
This can be better illustrated in the
is Instrumentation & Monitoring
horizontal and vertical alignment
following Figure 6.
(I&M). A well-engineered and
(i.e. curvature radii and gradient)
Another significant factor is the
implemented
I&M
scheme,
and others.
alignment of the tunnel, both in
constitutes the "eyes and voice" of
Shallow tunnels, primarily those
horizontal and vertical meaning.
Very steep gradients, sudden and
continuous changes in driving
directions and curvature radii
could impact the constructability,
compromise structural integrity
and lead to damages and failures.
Locality
The
location
where
the
underground structure is built
plays a diversification role on the
profile of a tunnel failure. Due
to current trend of urbanization
the project, as forms the only way
located in urban or inhabited
and the emerging demands
of obtaining real time information
areas can prove to be particularly
for infrastructure projects, more
about the structure's response
hazardous,
especially
when
underground activities are taking
and behavior. Hence, it allows
combined with overlying low-
place in urban areas and major
for realistic evaluation of the
bearing geological formations. The
cities. Nonetheless, a significant
existing insitu stability conditions,
exposure to the affected third party
percentage of tunnel works forms

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