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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 !!