stephen bateson, irish rail

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