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Iarnród Éireann/Irish Rail Risk Management and Scour Protection Works
on Masonry Arches and Piers
Assessment & Maintenance of Masonry Arch Bridges
Engineers Ireland
29th January 2016
Stephen Bateson BSc (Eng) Dip Eng Dip Hy & Geo Eng CEng MIEI
Principal Engineer - Structures
Background
Iarnród Éireann has 5200 bridges in total.
2182 are termed under-bridges
478 of these span over watercourses.
The majority of our structures spanning over water have some form of masonry support in or adjoining the
watercourse.
This presentation will include both masonry arch structures and structures with masonry piers
in/adjoining watercourse that are maintained by IE as part of the Bridge Maintenance Plans over the
Network.
The characteristics of the bridge assets structures (width, clearance, alignment & position) are set by a
track alignment that is in the region 150 years old.
The piers may be skew to the river to maintain track alignment.
The spans may be short and multiple.
The bridges were constructed to the design and requirements of the day.
Background
Historically the maintenance of the railway infrastructure, including railway
bridges has experienced under investment.
This has affected the implementation of data capturing and studies as well as
physical maintenance works.
The present investment level, provided by the MAC (Multi Annual Contract)
is still below that required to achieve a steady state level, therefore as the
assets get older they require greater funding.
Significant works have always been undertaken and a relatively large
number have been completed in recent years.
Background – Examples of Scour Repair Works
Background – Examples of Scour Repair Works
Development of the Maintenance Process
From 2005 IÉ has been formally undertaking Underwater Bridge inspections as
part of the bridge inspection programme.
This was originally based on a limited number of what were deemed high risk or
principal structures.
In 2009 a scour vulnerability rating was included within the deliverable of a
Bridge Scour Inspection (BSI).
This programme was widened to include for a full baseline of all bridge structures
(span <1.8m). The number of structures inspected was 105.
Following organisational change in 2010 the process has evolved into a risk based
process to prioritise the maintenance works on scour protection of bridges.
Development of the Maintenance Process – Comparison with other UIC companies
Management Policy
These are now managed in accordance with Standard CCE-TMS-415 “Flood and Scour Management Standard”.
•The policy of this is to manage the risk posed by hydraulic action on railway infrastructure.
Flood & Scour Management Process
The process involves
Screening Stage Bridge Scour Inspection BSI
Initial Assessment Stage Bridge Hydraulic Assessment
Detailed Assessment & Design Stage Bridge Scour Countermeasure
Stage 2 Assessment
Re-assessment Stage Re-inspection
Scour Inspection
Hydraulic Assessment
Counter - measure Design
Re-Assessment
BFI
BSI -Screening Stage
Bridge Scour Inspection
Cyclic Inspection 1,3,6 or 10 yrs
BHA - Initial Assessment
Bridge Hydraulic Assessment
Scour Vulnerability Rating (SVR)
Risk Rating generated
BSCM
Detail Assessment & Design
Bridge Scour Countermeasure Design
Design to C742 – Ciria Manual
Flood & Scour Management Process
Bridge Scour Inspection BSI
The process involves a BSI – Bridge Scour Inspections as the basis for the process.
Cyclic Inspection that delivers a factual report of the underwater structure and the river channel.
This is undertaken by an external team that tenders the work from a Framework list.
This factual report gives details of the condition of the river channel and the structure 1 m above water height of the high water mark. The Inspection survey varies based on the Category of the Structure.
Category 1: Inspection of the bridge, through touching and probing of all elements of the bridge to a height of 1m above the highest water level and a riverbed survey to an extent of 60m upstream and 60m downstream of bridge.
Category 2: Inspection of the bridge, through touching and probing of all elements of the bridge to a
height of 1m above the highest water level and a riverbed survey to an extent of 300m upstream and 60m downstream of bridge.
Category 3: Inspection of the bridge, through touching and probing of all elements of the bridge to a
height of 1m above the highest water level and a riverbed survey to an extent of 20m upstream and 20m downstream of bridge.
Bridge Hydraulic Assessment BHA
The Next Step after the BSI cycle involves review of factual reports by Hydrologist
for a Hydraulic Assessment.
BHA – Bridge Hydraulic assessment
A Hydrologist undertakes this stage of the process and using the BSI reports a
SVR (Scour Vulnerability Rating) is calculated.
This SVR is generated from a screening process developed by the US Forestry
Service and uses variables from both the structure and the river channel to arrive
at a score out of 67. The higher the score the higher the vulnerability to scour.
The Hydrologist specifies the return period for the cyclic inspection. 1, 3, 6 or 10
years. For structures considered high risk a shorter return cycle may be advised.
Bridge Hydraulic Assessment BHA
Risk Level
Intervention Required
Return Period for BSI
Low Risk
No Planned Works
6 years
Medium Risk
Plan works long term 3 years
High Risk
Plan Works short term
< 1 years
Bridge Foundation Inspection BFI
One of the larger contributors to the SVR score is that of the known depth
and characteristic of the foundations.
BFI – Bridge Foundation Investigation are undertaken.
Historically bridge records did not include foundation details, unless by
exception, ie UBB 82 Boyne Viaduct.
A programme was commenced to use Site Investigation techniques to
determine the depth, form and dimensions of foundations. The
characteristics of the underlying strata was also determined where possible.
These are costly and require careful programming to avoid flooding and planting
seasons that effect the accessing of the sites.
Bridge Foundation Inspection BFI
Investigation involves: •Geology Study •Field Work – coring holes, insitu testing (cobra probe, seismic Refractions, Resistivity Imaging) Determined in this case that there were “stone foundations supported by granite bedrock”.
Position of Rock Core
Bridge Foundation Inspection BFI
Following reduction in
flood levels and inspection
of bridge elements, it was
possible to allow a re-
opening of the line within 3
days, due to the
knowledge that the bridge
piers were founded on
granite bedrock. Recent Flooding incident in Enniscorthy UBR323.
Bridge Foundation Inspection BFI
Flooding at Enniscorthy December 2015
Detailed Assessment & Design
This stage of Detailed assessment and design involves:
Site Inspection/survey.
Selection of countermeasure design C742 “Manual at Scour Bridges and Other Hydraulic
Structures”
Undertaken hydraulic equations
Based on DMRB Advice note on “Assessment of Scour at Highway Bridges”, Vol 3,
Section 4 Part 21 BA 74/06. Q2oo is used as Flood event.
Where river gauged, design flow is calculated
Where river un-gauged, design flow calculated on catchment area. OPW data.
Values used in HEC-Res model to calculate scour depth. Generally a 2 D model.
Method statement of proposed works, incl environmental aspects & Fisheries etc.
Preparation of a final report to include calculations, construction drawings and method
statement.
Countermeasure Design Selection process This is a basic check list that gives indication of the suitability of the repair chosen for a given location and budget.
Case Study 1
UBC 45 Sallins – Dublin to Cork Line
SVR 51/67 Medium to High Risk
River Liffey, near Sallins, Co Kildare.
A scour depression upstream side of Central Pier
Large blockage on Left span opening.
Work done to remove blockage and open channel
Install rip rap to central pier
Maintenance works to masonry piers and abutments
Design – UBC 45
UBC 45 Dublin - Cork Line
UBC 45 Dublin - Cork Line
Temporary Sandbagging to prepare for installation of rip rap to front of pier.
Case Study 2
UBC 289 Dublin to Cork Line
SVR 32/67 Medium Risk
Undermining of concrete apron in main channel
Large Depression downstream of Concrete Apron
Erosion along downstream abutment
Concrete apron removed and replaced with dished rip rap.
Obstruction removed to provide for all 3 channels to be available.
Armour provided for river banks
Design - UBC 289
Design – UBC289
Rep Rap and rock armour to river banks
Completed structure rip rap & armour
Dished rip rap apron
Case Study 3
UBS 507 Dublin to Sligo Line
SVR 37/67 Moderate but other defects present.
Undermining of Upstream wingwall.
Erosion of channel bed.
Repairs to Arch
Installation of rip rap and approach
Protection armour.
Design – UBS507
Design – UBS507
UBS 507
Pre- works
Excavation works
Installation of rip rap in dry cell
Dry cell prior to installation of rip rap
Case Study 4
•UBE147 Limerick to Ennis Line •SVR 42/67 - Medium to High •Scour Depression along central pier . •Further scour occurred and works were programmed. • Concrete Apron with Approach Rip –Rap installed.
UBE 147
The completed project
Concreting works to span
Finished Rip-Rap
Design – UBE 147
