Iarnród Éireann/Irish Rail Risk Management and Scour Protection Works on Masonry Arches and Piers

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Gertrude Jefferson
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1 Iarnród Éireann/Irish Rail Risk Management and Scour Protection Works on Masonry Arches and Piers Assessment & Maintenance of Masonry Arch Bridges Engineers Ireland 29 th January 2016 Stephen Bateson BSc (Eng) Dip Eng Dip Hy & Geo Eng CEng MIEI Principal Engineer - Structures

2 Background Iarnród Éireann has 5200 bridges in total 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.

3 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.

4 Background Examples of Scour Repair Works

5 Background Examples of Scour Repair Works

6 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.

7 Development of the Maintenance Process Comparison with other UIC companies

8 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.

9 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

Flood & Scour Management Process Scour Inspection BSI -Screening

BHA - Initial Assessment Re- Assessment Counter - measure Design

Scour Countermeasure Design Design to C742 Ciria Manual Bridge

10 Flood & Scour Management Process Scour Inspection BSI -Screening Stage Bridge Scour Inspection Cyclic Inspection 1,3,6 or 10 yrs BHA - Initial Assessment Re- Assessment Counter - measure Design Hydraulic Assessment BSCM BFI Detail Assessment & Design Bridge Scour Countermeasure Design Design to C742 Ciria Manual Bridge Hydraulic Assessment Scour Vulnerability Rating (SVR) Risk Rating generated

11 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.

12 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.

13 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

14 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.

$seismic Refractions, Resistivity$ that there were stone foundations

15 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 reopening of

16 Bridge Foundation Inspection BFI Following reduction in flood levels and inspection of bridge elements, it was possible to allow a reopening of the line within 3 days, due to the knowledge that the bridge piers were founded on Recent Flooding incident in Enniscorthy UBR323. granite bedrock.

17 Bridge Foundation Inspection BFI Flooding at Enniscorthy December 2015

18 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.

19 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.

20 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

22 Design UBC 45

23 UBC 45 Dublin - Cork Line

24 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

25 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

26 Design - UBC 289

27 Design UBC289

28 Rep Rap and rock armour to river banks

29 Completed structure rip rap & armour Dished rip rap apron

30 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.

31 Design UBS507

32 Design UBS507

33 UBS 507 Pre- works Dry cell prior to installation of rip rap Excavation works Installation of rip rap in dry cell

34 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.

35 UBE 147 Concreting works to span The completed project Finished Rip-Rap

36 Design UBE 147

Strategies to Mitigate Scour Critical Structures

U.S. Department of Transportation Federal Highway Administration Strategies to Mitigate Scour Critical Structures Dan Ghere Hydraulics Engineer (708) 283-3557 dan.ghere@dot.gov Support Material HEC 23,