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Geosynthetics - A Network Rail

Perspective

Peter Musgrave Lead Track Bed Design Engineer IEng MICE FPWI

Levente Nogy Senior Design EngineerCEng MICE FPWI

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Geosynthetics A Network Rail Perspective

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Geosynthetics Approval Process

Examples of Problem Sites

Subgrade Erosion Slurring Mechanism

Site Investigation & Modelling Techniques to Investigate &

Analyse Track Bed Problems

Geosynthetics used in Track Bed

Presentation Covers the Following:

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Geosynthetics used in Track Bed

Network Rail

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Geosynthetic Types Criteria for Use

Normal Separator (can be woven, non-woven, needle punched, heat bonded)

Protect existing or new blanket and prevent migration of fines into the ballast

Robust Separator (consists of two

layers of geotextiles separated by mesh

grid or a very strong single layer material)

Coarse granular materials where there is a risk of abrasion and minor sub-grade erosion

Grid Reinforcement (Large aperture, bi-axial or tri-axial)

• All conditions where settlement / differential settlement is a problem• Where soft ground conditions are present

• Through level crossings (no shallow bedrock)• Where saturated formation which may behave like a soft formation is identified

• Transitions between structures and abutting plain line, with variable track stiffness

Sand Blanket Replacement

Geocomposite (10mm thick), or similar

Where sub-grade erosion is present or materials are susceptible to erosion

Geocells• Where extremely soft underlying conditions are present• Transitions to very stiff structures where the track stiffness needs to be

regulated

Types of Geosynthetics

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Impermeable Membranes

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Impermeable Membranes

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Site Installation Geotextile separator

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Site Installation Geotextile and Geogrid

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Site Installation Sand Blanket

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Drainage Design

Drain where Sand Blanket is installed

Drain where no Sand Blanket is installed

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Geocell Installation Methodology

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Geosynthetics approval process in Network Rail

Geosynthetics

Approvals Process

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Geosynthetics Volumes Annually (estimated)

Sand Blanket Replacement Geocomposite 20 miles

Combination - GeoGrid + Separator 12 miles

Biaxial/Triaxial Grids 50 miles

Robust Separator 50 miles

Geotextile Separator 28 miles

Trench Liner Geotextile Filter 11 miles

GeoCell 5 miles

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Geosynthetics approval process in Network Rail

• Satisfy a trackbed improvement requirementBusiness

Need

• Certificate of Authority for Product Trial• Time and Site specific

• Trial Success Criteria to measure the results of the trial

Product Trials

• Written report to validate that the success criteria have been achieved

Full Acceptance

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Geosynthetics approval process in Network Rail

• Section 1 Acceptance process details

• Section 2 Compliance with standards and ownership

• Section 3 System safety

• Section 4 Product function

• Section 5 Product reliability • Section 6 Configuration data

• Section 7 Network Rail integration tasks

• Section 8 Authorisation, date and sign-off

The requirements are broadly grouped in sections covering:

Acceptance Requirements for Railway Infrastructure Products and Systems

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10kN/m2

Release Valve

Water

Tracktex

Examples of Test Apparatus

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Extracts from NR Geosynthetics Specification

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Examples of Problem

Sites

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Failed Site Examples

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We can avoid all this!!!

Failed Site Examples

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SUBGRADE EROSION

SLURRYING

MECHANISM

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SLURRY – THE PROBLEM

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SLURRY – THE BARRIER

Preventing Surry Pumping

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SLURRY - PREVENTION

Preventing Slurry Pumping

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Critical velocity – Case study

(Beattock Summit)

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Critical velocity – Case study

(Glasgow St)

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Case study (Willesden Hump’s)

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Site Investigation & Modelling Techniques to Investigate & Analyse Problem Sites

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Finite Element Modelling

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Finite Element Modelling (video)

SHORT VIDEOS

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Ground Investigation Report Site Schematic

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Critical velocity – Case study

(Kintbury)

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Track deflection

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Failure Mechanism

High dynamic forces at

edge of the embankment

High stress in ballast

Ballast breakage

and voiding

Track settlement

Poor track drainage

Significant difference in

track stiffness

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Ballast stress

Stress on ballast &

subgrade is increased

by 2X

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Thank you !!