Environmental Engineering Reference
In-Depth Information
overturning). When inspectors override assess-
ment of PFs they should note the reasons for this
in their inspection record.
The standard approach to the calculation of the
FIs could be performed during or after inspection.
are some similarities between them. The guidance
(flowcharts and tables) provided attempts to reduce
this problem by highlighting any distinguishing
features for each.
If a particular failure mode is self-evidently
occurring or is known to dominate for a given
asset, the inspector has the option to ignore this
step and move straight onto step 2 taking the
'Override' option. This allows the inspector to
override the condition indexing process where
there is an obvious failure occurring. This elim-
inateswasted inspection time in the assessment of
performance features that will not be needed to
identify the asset CI.
As with the current inspection method, the
inspector should also be encouraged to add recom-
mendations or notes onto the inspection record.
This could be additional detail regarding the con-
dition or confidence assigned to a PF, potential
actions or maintenance work that is required, or
notes regarding the conditions under which the
inspection was carried out.
Calculation of the asset condition index
This can be done on site or after inspection and be
easily automated as with the previous step. Once
the asset CI has been calculated, the condition
indexing process is complete for that asset.
The asset management system will then be used
to analyse the inspection results and determine
an appropriate course of action. As with the cur-
rent inspection method, the inspector can
decide whether to add a recommendation regard-
ing the nature or urgency of any intervention
required for the asset such as remedial works or
replacement.
Condition indexing for earth embankments
Earth embankments form the majority of linear
flood defences in the UK, especially in rural or
semi-rural areas. They can have a very long life-
span given good local soil conditions and regular
maintenance to ensure performance. Embank-
ments are commonly subject to settlement over
their lifespan due to the consolidation of the un-
derlying soils. Local geotechnical or hydrological
processes can cause movement or deformation
of the embankment, which, if left unchecked or
uninvestigated, can lead to failure of the embank-
ment through a number of mechanisms, some of
which will be described.
Embankments are susceptible to erosion of
their fill material without surface protection. All
earth embankments employ some form of surface
protection to alleviate this problem. In many
instances grass cover is sufficient to protect the
embankment from erosion. Where hydrological
loading is more extreme, due to erosive currents
or regular overtopping of the embankment crest,
other forms of revetment are applied to an em-
bankment to reduce erosion of the embankment
material.
Calculation of the failure mode indices
This stage involves the calculation of the FI scores
for an asset. This can be achieved in two ways:
.
Override
- Where a failure mode is self-evident-
ly dominating the inspector can assign a condition
score directly for the FI thereby eliminating the
unnecessary assessment of PFs for an obviously
occurring failure of the asset.
.
Standard
- Calculation of the FIs from the as-
sessed PFs using contributions scores and the
formulae given earlier.
Override should only be used where the nature
of the failure occurring is obvious. This could be
due to the inspector's detailed knowledge of the
asset, data obtained in the pre-inspection stage and
confirmed on site, or the imminent and self-evi-
dent failure of an asset. For example, if the inspec-
tor arrived at a vertical wall structure to find the
wall leaning into the river at an anglewith obvious
and severe movement of the structure having
occurred, the inspector could ignore the assess-
ment of individual PFs and assign a condition
grade 5 to the relevant failure mode (in this case,
