Design of Picton Railway Overbridge for Mine Subsidence

Design of Picton

Railway Overbridge

for Mine Subsidence

Geraint Jones

Long Bai

Small Bridges Conference

24 November 2015

>Project Background

>Longwall Mining

>Location & Setting

>Proposed Works

>Stakeholders

>Program Milestones

>Detailed Design

> Mine Subsidence

> Articulation

> Spherical Bearings

> Modular Joint

> Maintenance Manual

>Conclusions

Introduction - Presentation Structure

Longwall Mining

Location & Setting

Proposed Works

Stakeholders

>Oct 2014 Commence Detailed Design

>Jan 2015: Detailed Design Complete

>Mar 2015: Tender Period

>May 2015: Award Contract

>June 2015 Commence Construction

>Nov 2015: Demolish Existing & Open New Bridge to Traffic

>Dec 2015: Anticipated first impact of Longwall

>Jan 2016: Longwall expected to be directly under the Bridge

>Mar 2016: Longwall expected to be complete

Program Milestones

Erection of Bridge Girders

Demolition of Existing Bridge

Bridge Design

1. Design Strategy

2. Bridge Articulation

3. Mining Subsidence Movements

4. Maintenance

5. Conclusion

Bridge Geometry

Design Strategy

>Design Guidance: BD10/97

>Special consideration is required if the

displacement between two points exceeds

1/1000 times the distance

>Mine subsidence prediction was carried out by

Mine Subsidence Engineering Consultants

(MSEC)

>Not economical to design all the elements and

connections to accommodate the worst

predicted movement

>Key challenge: A economical articulation

system that requires minimum intervention and

adjustment during or after the mining activities.

Mine Subsidence Movement Register

>Subsidence Movement Scenario

>Potential Response of Overbridge

>Potential Impact on Overbridge

>Predicted Movement

>Design Strategy

>Proposed Design Capacity

>Subsidence Management Strategy

>Trigger Level

Mine Subsidence Movement

Subsidence movement

scenario

Predicted Movements

1% Probability 0.05% Probability Worst Observed Maximum

Closure between

abutments

80 mm 230 mm 330 mm 500 mm

Opening between

abutments

35 mm 70 mm 80 mm 150 mm

Lateral differential

movement between

abutments

40 mm 80 mm 84 mm 150 mm

Vertical differential

movement between

abutments

50 mm 100 mm 330 mm 400 mm or 10mm/m

whichever is greater

Uniform lateral tilt

N/A N/A - 10mm/m

Transverse differential tilt

(twist) between abutments

- - - 10mm/m

Curvature of ground at

abutment transverse to bridge

- - - Hogging or sagging

curvature of 0.10km-1

Tension strain of ground at

abutment transverse to bridge

1.5mm/m 2.9mm/m - -

Compression strain of ground

at abutment transverse to

bridge

-3.5mm/m -9.7mm/m - -

Articulation

Abutment A

> Modular Expansion Joint

Abutment B

> Strip Seal Expansion Joint

Girders

> Spherical Bearings

Traffic Barrier Connector

Cover Plate

Safety Screen

Bearings & Lateral Restraints

Abutment A

> Free floating bearings under all girders

> Later restraint block between two middle girders

Abutment B

> Free floating bearings under two outer girders

> Fixed bearing under middle bearing

Articulation Movement Capacity

Element Opening Closing Vertical

Rotation

Horizontal

Rotation

Modular Expansion

Joint (Abutment A)

185 mm 535 mm +/- 0.03 rad +/- 0.01 rad

Strip Seal Joint

(Abutment B)

82 mm 43 mm - -

Free Floating Bearing

(Abutment A)

185 mm 535 mm +/- 0.03 rad -

Free Floating Bearing

(Abutment B)

28 mm 28 mm +/- 0.03 rad -

Traffic Barrier

Connector

120 mm 100 mm - -

Cover Plates 100 mm 230 mm - -

Safety Screen 55 mm 20 mm - -

Predicted conventional closure: 20 mm.

1 in 100: 80 mm

1 in 2000: 230 mm

Worst observed: 330 mm

Maximum Predicted: 500 mm

Closure Between Abutments

Opening Between Abutments

Predicted conventional opening: 25 mm.

1 in 100: 35 mm

1 in 2000: 70 mm



Lateral Movement Between Abutments

1 in 100: 40 mm

1 in 2000: 80 mm



Vertical Movement Between Abutments

Predicted conventional tilt: 2 mm/m.

1 in 100: 50 mm

1 in 2000: 100 mm


Maximum Predicted: 10 mm/m or 400 mm (whichever is greater)

Modular Expansion Joint

Picture Courtesy to Mageba

Spherical Bearings

1. Concave lower part

2. Sliding sheet (UHMWPE - ultra-high

molecular weight polyethylene)

3. Convex polished chrome surface

4. Sliding sheet (UHMWPE)

5. Sliding plate

6. Guide bars

7. Anchor dowels

Picture Courtesy to Mageba

Maintenance

Asset element/Sub-element Minimum Design life (years)

Permanent Structural Elements 100

Spherical Bearings 40

Bridge Joints – Joint sealant 15

Bridge Joints – Expansion joint rubbers 35

Safety Screens – Protective Coating 15

Asphalt Wearing course 40

Traffic Barrier Railings – Protective coating 20

>Design Life of Bridge Elements

>Maintenance Diary of Bridge Elements

>Inspection and Maintenance Instructions

>Work-As-Executed Drawings

The design for this single span bridge of modest dimensions was relatively

complex due to the requirement that the bridge should accommodate potential

significant mining induced ground movements without intervention or adjustment.

Through consultation with a wide range of parties an efficient and robust design

solution was achieved.

The existing bridge was demolished and the new bridge constructed with

minimum disruption to road and rail users and with no delay to the longwall

mining operations.

Conclusion

Acknowledgements

Kevin Golledge Tahmoor Coal

David Talbert Tahmoor Coal

Ian Sheppard Tahmoor Coal

Daryl Kay MSEC

Mark Dolan Robson Civil

Virendra Ghodke Mageba

Design of Picton Railway Overbridge for Mine Subsidence

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