Environmental Engineering Reference
In-Depth Information
Table 6.3
Failure Mode Indices with Associated Confidence Range Values
Failure mode index
Slope instability
Piping
Back
ll washout
Overtopping leading to breach
Assigned condition
3.25
1.90
2.25
3.00
Minimum con
dence
2.30
1.80
1.80
3.00
Maximum con
dence
3.25
1.90
2.25
3.00
337kmof defence assets, representing awide range
of asset types and conditions, were inspected cov-
ering the whole of the Thames Estuary region.
Results fromthe use of themethod by a number
of experienced and non-experienced inspection
staff were very promising. The method was found
to be much more consistent in the attribution of
asset condition. There was little difference be-
tween assessments produced by experienced and
non-experienced staff - a significant improvement
over the current inspection method.
Overall asset condition was also found to be
assessed as being in better condition thanwith the
existing inspection method. This was to some
extent expected since the method is focused on
assessing likely performance based on visual con-
dition rather than purely the visual condition. It is,
however, a crucial and significant vindication of
the work. A primary motivation for the project
was the hypothesis that the existing inspection
method graded asset condition more severely
than was necessary due to its focus purely on
visual condition without explicit linkage to likely
performance. However, this improvement in asset
condition will need further research and trials to
establish its accuracy.
Critical feedback relating to the complexity of
inspecting composite assets and specific concerns
on individual flowcharts were also recorded and
will be used to further refine the method.
Overall, the results of this initial live trial were
encouraging and will provide feedback and expe-
rience for any future implementation of the meth-
od nationally by the Environment Agency.
cally assess the likely performance of an asset
under loading and is overly concerned with as-
sessing purely visual deterioration, which might
not significantly impact on performance.
A revised method has been described that
represents a measured step towards a more
performance-based assessment using visual find-
ings. This method draws upon recent research in
performance modelling and includes uncertainty
assessment and potential failure modes for key
asset types. The method is backed up through
flowchart-based guidance and has been deve-
loped in conjunction with leading industry prac-
titioners and researchers.
A number of case studies utilizing well-known
assets were developed to provide proof of concept,
and the method has been adapted and employed in
large-scale live trials as part of the TE2100 project.
Results from case studies and the live trial have
been very encouraging, and it is envisaged that the
method will form the basis for future inspection of
assets in the UK.
References
Environment Agency (2007) Managing Flood Risk: Con-
dition Assessment Manual. Document
reference
166_03_S001.
Halcrow (2004). NADNAC - National Assessment of
Defence Needs and Coasts. Halcrow in association
with HR Wallingford, 2004.
HR Wallingford (2003) Reducing the Risk of Embank-
ment Failure under Extreme Conditions.Defra/
Environment Agency Flood and Coastal Defence
R&D Programme.
HR Wallingford (2004) Performance and Reliability of
Flood and Coastal Defences. Defra/Environment
Agency Flood and Coastal Defence R&D Programme.
HR Wallingford & University of Bristol (2004) Risk
Assessment
Summary
The current method for the visual inspection of
flood defence assets in the UK does not realisti-
for Flood and Coastal Defence for
