Current RRUK Research into Railway Track and Sub-Base Performance

William Powrie, University of Southampton Principal Investigator, RRUK

University of Southampton: Jeffrey Priest, Li-Ang Yang, Louis le Pen, Daren Bowness University of Birmingham: Michael Burrow University of Nottingham: Glenn McDowell, Mingfei Lu Outline of Presentation

• Rail Research UK –Aims • Project A1: understanding track/sub-base performance – Background – Finite element analyses & laboratory tests – Field monitoring • Other RRUK track projects What is RRUK?

• A virtual centre for based rail systems research • Thirteen research groups in nine universities • Jointly led by the Universities of Birmingham and Southampton • Multidisciplinary • Civil, Computer, Electrical, Electronic, Environmental, Mechanical and Systems Engineering; Computer Science; Metallurgy and Materials; Noise and Vibration; Psychology; and Transport Economics • EPSRC funding • RRUK1 - £4.2M (May 2003 – September 2006) • RRUK2 - £3.7M (September 2006 – March 2010) RRUK Aims

• To support the UK railway industry by providing a focal point for university-based rail systems research • To facilitate research that will • Improve the safety, reliability and capacity of the rail network • Reduce the impact of railways on the environment • Make rail travel more attractive for passengers • Improve industry practice and inform policy development by • Providing a strong coherent academic community • Enhancing the science base for rail systems research • Working in partnership with industry Industry Engagement

• Supported by major industry stakeholders • RSSB, SRA, , ATOC, AEAT Rail, LUL, , Corus, Carillion, Scott Wilson • Organisations providing assistance with current projects • AEA Technology Rail, Arup & Partners Ltd, ATOC, Atkins Rail, Rail, Bombardier Transportation, British Geological Survey, Carillion Rail, CIRIA, Corus Rail, DfT, DB Systemtechnik (Germany), EWS, Fugro, Gary Davies Associates, Go-Ahead Group, Greater Passenger Transport Executive, Hitachi, Jarvis Rail, JR Group (Japan), London Underground Ltd, Metronet Rail BCV, Mott MacDonald, National Express Group, Network Rail, Network Rail CTRL, NS (Netherlands), ORR, Pandrol, Porterbrook Leasing, Rail Passenger Demand Forecasting Council, Rail Safety and Standards Board, Railway Forum, Renfe (Spain), Scott Wilson Pavement Engineering, SJ Green Cargo (Sweden), SNCF (France), Spoornet (South Africa), and UIC (France) • RRUK has gained acceptance and credibility in a traditionally conservative and inward-looking industry External Involvement

• RRUK members involved in: • EURNEX – European Rail Research Network of Excellence • ERRAC – European Rail Research Advisory Council • AGRRI – Advisory Group for Rail Research and Innovation • V/T TAG – VT/ SIC Technical Advisory Group • IAVSD Board – International Association of Vehicle System Dynamics • IMechE – Institution of Mechanical Engineers, Railway Division Board • Passenger Demand Forecasting Council (comprises TOCs, DfT, NR, ORR) •Railway Forum • BSI – British Standards Institution • CEN – European Committee for Standardization • ISO – International Organization for Standardization Research Themes and Projects Project A1: Background

• Current codes of track sub-base design are often: - recipe-based - unscientific - inconsistent -wrong! Current design specifications for ballast thickness

EmpiricalEmpirical Analytical Analytical

Li & Selig (1998) BR (60s & 70s) Network Rail 039 (2004) AREA (1994) UIC 719R (1994)

Recipe based Performance based Recipe based PSlide:erformance Michael Burrow, based University of Birmingham Cyclic loading effects build-up of strain in drained conditions

Cyclic Loading (axial & torsiona l) - Stress Strain Deviator stress: 30kPa, Effective conf ining p ressure: 30kPa 35

30

25 ) a P k ( 20 ress t S r 15 o at

Devi 10

5

0 0.000 0.002 0.00 4 0.006 0.008 0.010 0.012 0.014 0.016 0.01 8 Local Axial Strain Cyclic loading effects build-up of pore pressure in undrained conditions

Cyclic Loading (axial & torsiona l) - Pore Pressure Change Deviator stress: 30kPa, Effective c onf ining pr es sure: 30k Pa 35

30

25 ) a P k

( 20 ss re st r 15 o at vi e

D 10

5

0 0 5 10 15 20 25 PWP ( k Pa) Cyclic loading effects

Migration of stress state to undrained failure

20

18

16 ) a P k 14 J ( , t

an 12 ri va

n 10 i s res

t 8 s c i r

o 6 at vi e

D 4

2

0 15 20 25 30 35 40 45 Mean effective stress, p' (kPa) Soil is not elastic high stiffness at small strains

350 t 300

250 s

200 Euv (MPa) 150

100

50

0 0.001 0.01 0.1 1 10 Loc al axial s train (%) Undrained stiffness-axial strain for Atherfield I Clay specimen under monotonic loading (po’=360kPa) Case Study - Leominster

•Track quality problems reported frequently •Frequent maintenance Ballast

900 – 1300 mm Sub-ballast

Recommended depth of trackbed layers (m) Why are there problems if all standards Li Selig UIC BR NR WJRC indicate depth of trackbed layers is 0.86 0.82 0.97 0.49 0.20* sufficient? Project A1 - aims

• Assess the robustness of traditional design using a modern soil mechanics approach • Explore the potential of a more fundamental understanding to guide design, and assess performance and maintenance/remediation options Economic importance

• Track expenditure for rehabilitation of 26 tonne/axle heavy haul track formations 3% 7% 2% P-way 2% Earthworks construction 4% O.H.T.E. construction 58% Signals construction Transtel Telecommunication Laboratory services & surveys Project management 24% Project A1

• Project A1 takes a step back: it aims to develop a full scientific understanding of the load/deformation response of the track foundation

Instrumented sites – field data Advanced laboratory testing Numerical modelling Modern soil mechanics Evaluation of design methods More fundamental understanding

Improved geotechnical approach to design / remedial work Project A1 - Methods

• Determine the stress paths followed by soil elements below railway tracks (FEA) • Assess soil behaviour in these stress paths (laboratory testing) • Develop methods of measuring track and ground movements/stresses during train passage • Field measurements • Analyse observed behaviour in terms of simple and more complex models • Produce revised design guidance based on consideration of whole life costs Finite Element Analysis Stress Distribution

Vertical stress contour at centre plane (compressive stress as negative) Calculated principal stress rotations

(a) Wheel load = 125 kN (b) Wheel load = 125 kN 100 100

ss s 90 90 g s re e g e r e

t 80 st 80 : d l α : d a l s , α p l 70 , pa l

70 a i ci a ic n i c t 60 i r r inc 60 r e p r p

v 50 o

50 e e vert jor h h a

t 40 t

o 40 maj f o m t e o 30 of v 30 n i ve t t o i i t t ion 20 la a t 20 c e c e r e r rel 10 r i

10 Di D 0 0 0123456 7 0123x/S 456 7 x/S

0.13S below the soffit of sleeper 0.49S below the soffit of sleeper 1.67S below the soffit of sleeper

PSR under different initial stress states (a) K0 = 0.5 and (b) K0 = 2.0 Laboratory element testing options

cyclic triaxial test cyclic hollow cylinder test Hollow cylinder apparatus Hollow cylinder apparatus

W σ MT zz

τzθ Po pi σθ

τθz

σr

(b)

ro

σ1 ri α

r α θ σ3 σ z 2

(a) (c) Idealised stress paths in HCA

0. 05 C ycl e 0. 04

0. 03

0. 02 sb σ / ij

σ 0. 01 ∆

0. 00

-0 .0 1

-0 .0 2 01234567 x/ S ∆σ xx ∆σ yy ∆σ zz- ∆σ xx ∆ tx z A p pr ox im at ed ∆σ zz- ∆σ xx A ppr ox im at ed ∆σ xx & ∆σ y y A p pr ox im at ed ∆ tx z Typical SA engineered formation grading curves

100

80

60

40 D

Percentage passing (%) 20 C Grading envelope of B Coal Line material 0 A 0.0001 0.001 0.01 0.1 1 10 100 Particle size (mm) Principal Stress Rotation (PSR)

25

Specimen 2A:A 7% clay, OCR=15, K0=1, no PSR

) Specimen 3A:A1 7% clay, OCR=15, K0=1, with PSR a 20 (last 10 cycles2 before failure) Specimen 3A: 7% clay, OCR=15, K =1, with PSR (kP A 0 t (first 10 cycles) oc 2 τ

ss, 15 e r

st Cyclic triaxial test 10 al shear hedr a 5 Oct Cyclic hollow cylinder test 0 -40 -30 -20 -10 0 10 20 30 40

Direction of σ1 relative to the vertical, α (degrees) Axial Strains with and without PSR

Sample A Axial Strains with and without PSR

Sample D Future laboratory testing

Future work will investigate the effect of various parameters on the resilient modulus of soils subject to principal stress rotation, such as

• Particle size • Particle shape • Drained vs undrained conditions • Frequency of loading Site Monitoring

•Site Data • Essential for validation of models and for testing theories • Need to develop instrumentation that is: • Reliable • Installed quickly - minimising disruption • Cheap • Site monitoring so far: • Crewe –Balfour Beatty Rail (completed) • Network Rail (CTRL) – (ongoing) • Loughborough –Great Central Railway (complete) • Bloubank, South Africa –Spoornet (ongoing) Measurement techniques

Remote video monitoring

Webcam captures digital video images of a ‘target’ from which displacement is calculated using computer algorithm.

Current webcam records at 30fps Measurement techniques

Geophones Cross section through track structure Front view of access pit Track structure (ballast, sleeper, rail)

A 200 A Access pit B B A 800

m

C 3 C D 200 C D D

Approx. 6 m 1 m

Geophones:- LF 24 – 1 Hz natural frequency Logged at 500Hz

Mounted on sleeper or positioned in borehole at differing depths in formation Site monitoring at Crewe - site layout Dynamic deflections – Video monitoring

1.0 Displacement from remote video 0.5 monitoring on ballasted track for a class 66 locomotive (13.25m bogie 0.0 )

m centre, 2.07m axle spacing)– high (m t n e -0.5 frequency displacement noise due cem

la to telescope vibration

Disp 1.0 -1.0

-1.5 0.0

-2.0 0 5 10 15 20 25 30 -1.0 Time (s) ment (mm) e lac

p -2.0 Dis Displacements for Class 66 locomotive on ‘slabtrack’ showing reduction in -3.0 ground born vibrations, bigger -4.0 deflections due to the softer pads on 0 2.5 5 7.5 10 12.5 15 ‘slabtrack’ Time (s) Video monitoring cont:-

4.0 1.0

Horizontal 3.0 Vertical 0.0 ) m m) m

m 2.0 ( t ( t n n e

m -1.0 me e e c c a l a l p p 1.0 s s i Di D

-2.0 0.0

-1.0 -3.0 0 5 10 15 20 0 1020 304050 Time (s) Time (s)

Video displacements for class 66 loco on Video displacements for two class 37 the slab-track (starts with leading axle of locomotives pulling 6 pairs of Intermodal locomotive stationery at target; loco then Freight Cars on the transition section accelerates away) between the ballasted track and the slab- track Geophones - typical velocity results

8

6

4

2 s)

/ 0 m m

( -2 y cit lo

e -4 V -6

-8

-10

-12 0 5 10 15 20 25 30 35 40 45 50 Time (s) Geophones - dynamic displacements

0. 08

0. 06 Overall displacement 0. 04 )

m 0. 02 m ( t n e 0 m ce a l

sp -0.02 i D

-0.04

-0.06

-0.08 0 5 10 15 20 25 30 35 40 45 50 Time (s) Channel Tunnel Rail Link

Channel Tunnel Li ne o f s ew er Lo nd o n

1210mm 1195mm 1195mm 1205mm 1200mm 1 200 mm 1 200 mm

S lee per No 1 No 2 No 3 No 4 No 5 No 6 No 7 No 8

G eo pho ne s & 91 .7 15k m fr om Lo nd o n W e bc am ta rge ts (3.42 7k m a lon g ch or d)

To monitor dynamic displacement during tunnelling under line 8 targets (and geophones) attached to sleepers Measurements taken before, during and after tunnelling Monitoring in addition to static measurements All trains captured were full Class 373/1 Eurostar sets with the trailers having a near uniform axle loading of approximately 15 tonnes. CTRL cont:-

0. 4

0. 2 Typical displacement response for

0 CTRL track. )

m -0.2 m ( t n e -0.4 m ce a l Lower plot shows variation in

sp -0.6 i D

-0.8 sleeper displacement for section of

-1 CTRL. Sleeper No 4 shows highest

-1.2 deflection and may be ‘hanging’. 10 12 14 16 18 20 22 24 26 28 Time (s)

Chan n el T unn el Li n e o f s e w e r L o ndo n

12 10 m m 1195 m m 119 5m m 1 205 m m 12 00 m m 1 200 m m 12 00 m m

S lee per No1 No 2 No3 No 4 No5 No 6 No7 No 8 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Dy n am ic s lee per dis pla ce me nts ( mm) CTRL cont:-

0.1 Comparison between Geophone Video geophone and PIV show 0 that both are in agreement. Using a frame rate of 30fps -0.1 for the video monitoring ) m

m equated to an image being

( -0.2 t

n acquired for every 880mm of e

m travel compared to 53mm for ce

a -0.3 l the geophones (500Hz). sp i

D Given these limitations both -0.4 methods easily capture the displacements due to -0.5 individual axles.

-0.6 6 6.5 7 7.5 8 8.5 9 9.5 10 Time (s) Loughborough

Investigation of embankment on Great Central Railway line near East Lake, Loughborough. Single line heritage track carrying gypsum to nearby factory Class 60 Loco pulling 18 wagons. Line limited to 10mph ~ 0.2Hz Joint monitoring with BGS and University of Birmingham Loughborough cont:-

Nearly 6mm of deflection was recorded for Class 60 Loco pulling 18 empty wagons. For the loaded train the deflections were so large the target moved out of the field of view of the webcam during the train passage. Manual estimates showed maximum deflections for wagons around 7.7mm. Sensitivity of geophone and filtering process underestimates deflections at low speeds Conclusions: Geophone and video monitoring

1) At line speeds of 45 – 100 km/h, measurements made using the two systems were in close agreement 2) At higher line speeds limitations arising from the frame rate of the webcam could lead to peak events being missed and the underestimation of deflections 3) At low line speeds below 48km/h the dominant frequency of the axles or bogies is below 1Hz; geophones will then tend to underestimate deflections because of filtering difficulties South Africa Railways

• Total: 22,298 km • Narrow gauge: 21,984 km 1.065-m gauge (10,436 km electrified); 314 km 0.610-m gauge • Note: includes a 2,228 km commuter rail system (2002) • COALink • Constructed in 1970s • Carries approx. 84m tonnes of coal per year • 580km of track • 60kg/m CrMn rail • Narrow gauge (3’ 6”) • 26 tonne axle weight • Trains comprise 200 No. 104-tonne trucks + 5 locos Measurement Techniques

Geophones Cross section through track structure Front view of access pit Track structure (ballast, sleeper, rail)

A 200 A Access pit B B A 800

m

C 3 C D 200 C D D

Approx. 6 m 1 m

Geophones:- LF 24 – 1 Hz natural frequency Logged at 500Hz

Mounted on sleeper or positioned in borehole at differing depths in formation Vertical displacements in formation

Vertical deflections recorded 1m below bottom of ballast for 100 tonne coal wagons. Smaller deflections for locomotive seen at front

Vertical deflections recorded 1.2m below bottom of ballast for same train passage, note reduced deflections Horizontal displacements

Close up of vertical deflections show global deflection for axle grouping (two axles at each end of wagon), with smaller movements observed for each axle

Close up for horizontal deflection at same depth show large displacements for each individual axle Future work

• Interpret field data with respect to simple (elastic foundation) and complex (FE) models • Characterise operational elastic parameters • Assess importance of PSR in the field • Appraise current design methods and suggest revised guidance • Assessment of sub-base/track/vehicle interactions • Whole life costing PhD project: track stability - aims

To investigate the lateral stability of the track/ballast interface under the action of loads applied by • Tilting trains cornering at high speed; Side-winds • Dynamic loads (hunting); Thermal effects in CWR

Idealisation of the track system and the sleeper / ballast interface load resistance

The track loading under investigation Track stability project: methods

• Test rig • Measurement of lateral resistance from base, shoulder and crib ballast • Geophone measurements • Measuring dynamic sleeper movements on a curve of the West Coast Main Line (WCML) • Modelling • Results from laboratory / field tests will be used to development conceptual and numerical models

Sleepers; rig under construction PhD project: ballast modelling - background

• Ballast particle shape and strength have important role in determining stiffness of trackbed and accumulation of permanent strain • Permanent deformation is caused by particle breakage (and rearrangement of particles) • Most degradation of ballast particles under cyclic loading is due to abrasion not bulk fracture

Irregular 2-ball clump Irregular shaped shaped with 2 clump with some clump asperities asperities Ballast modelling project - methods

• Particle scale modelling: PFC-3D • Irregular shaped clumps represent single ballast particles • Small spheres bonded to the surface of rigid clumps to provide a mechanism for abrasion • Box tests and triaxial tests to investigate the micro mechanical behaviour of the ballast Load against deformation for the box test on 2 ball clumps with 2 asperities Ballast modelling project - initial results

• Irregular clumps can provide particle interlocking and the more realistic load- deformation

Box test simulation using 2-ball response clumps with 2 asperities • Abrasion is necessary to give the correct response in terms of settlement as a function of number of loading cycles Load against deformation for the box test on 2 ball clumps with 2 asperities Opportunities for collaboration

• Joint research projects • Field monitoring • Funded research • Engineering Doctorate • Collaborative Training Account • Industrial CASE (Cooperative Awards in Science & Engineering) • Knowledge Transfer Partnerships • Master’s Training Packages Potential research projects

• A fundamental investigation into the mechanics and effectiveness of stoneblowing. • Mechanical stability of subgrade materials under cyclic loads involving principal stress rotation • An investigation into the mechanics of ballast during tamping – a granular material undergoing stress reversal • Effects of partial saturation on the strength and resilient modulus of subgrade materials • The effect of high speed trains on the stability of ballast Thank you for your attention