Page 365 - 360.revista de Alta Velocidad - Nº 5

A railway culvert maintenance management approach based on risk assessment techniques

The total economic impact is divided into the direct economic impact associated with
the repair / rehabilitation costs directly attributable to the competent administration
(representing on average 69% of the total economic impact) and the associated indirect
economic impact to the costs derived from the traffic disruption on the roadway and various
compensation costs, which are held by society (31% of the total). On the other hand, for the
purposes of the present study only the indicators of impact and economic risk are shown
since the impact and personal risk on the users of the road is assessed only in qualitative
terms.
Notice that probabilities and consequences values must be converted to qualitative scales
so that the qualitative assessed risk level can be obtained. A scale of 5 risk categories
defined by annual probability of failure and economic impact ranges (R1 to R5, where R1
is the highest level of risk) based on recommendations of other authors (Roads and Traffic
Authority, 2010) has been established. Applying this rating scale, less than 1% of evaluated
assets are in the R1 category, whereas in the majority of the studied cases (41%) the risk
level fits in the lowest category (R5).
The failure mechanism presenting the highest risk is the structural collapse of the culvert
barrel (directly related to the general deterioration condition observed inside the culvert
barrel) and erosion caused by overtopping flows (due to partial or total blockage / insufficient
hydraulic capacity during peak flows). Since many of culverts studied are above twenty five
years age and the impact caused by the structural collapse of the culvert barrel implies
the total cut of service in the roadway and the complete restitution of the culvert, the
incidence level on the total risk in this failure mechanism remains high.
On the other hand, the most common pathologies affecting culverts have been identified.
Each of these pathologies affects one or more failure mechanisms, depending on their
nature. The need to extract these risk factors from the final diagnosis is because they
represent the most reliable indicator when planning preventive repair and / or replacement
actions based on the preliminary diagnosis results. As shown in Table 2, the risk factor that
has the highest percentage of incidence on total risk is that related to the hydraulic capacity
of the culvert. This average value includes the cases where the culvert does not present any
specific pathology, so the remaining risk (100%) is due to the residual probability associated
with failure mechanisms triggered by rainfall events. In order of relevance, the pathologies
associated with the structural deterioration of the culvert barrels and headwalls at inlet or
outlets, partial or total blockage of the culvert barrel and undermining at inlet/outlet are
highlighted.

4. Conclusions and further implementation

In this section the potential of the culvert risk assessment methodology applied in the
development of systems of investments prioritization in the maintenance of this type of
structures has been discussed.

Once the preliminary diagnosis of the set of assets studied has been obtained, the following
level of development of the methodology is presented: the analysis of investments
in maintenance and its prioritization based on risk reduction criteria. The selected
rehabilitation measurements or remedial works in a particular culvert will be determined
in the first place for operational restrictions (the rehabilitation techniques depend, in
most cases, on the cross section typology, shape and material of the culvert barrel) and
in the second place for the study of the risk factor currently operating on the asset.
The cost of remedial works is determined according to the characteristics of the culvert
(general field measurements) while the repercussion in terms of risk reduction per year, is
evaluated considering the specific impact of every rehabilitation measurement in the global

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