University of Southampton Research Repository Eprints Soton
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University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS SCHOOL OF CIVIL ENGINEERING AND THE ENVIRONMENT TRACK BEHAVIOUR: THE IMPORTANCE OF THE SLEEPER TO BALLAST INTERFACE BY LOUIS LE PEN THESIS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY 2008 ACKNOWLEDGMENTS I would like to sincerely thank Professor William Powrie and Dr Daren Bowness for the opportunity given to me to carry out this research. I'd also like to thank the Engineering and Physical Sciences Research Council for the funding which made this research possible. Dr Daren Bowness worked very closely with me in the first year of my research and helped me begin to develop some of the skills required in the academic research community. Daren also provided me with some of the key references in this report, he is sadly missed. Network Rail, Tarmac, Pandrol and Corus steel must also be acknowledged for their support in kind. In particular John Amoore of Network Rail has been instrumental in arranging for some of the field monitoring work to take place on the West Coast Main Line. At the University of Southampton I have been able to benefit from the advice given by numerous members of academic and laboratory staff, in particular my thanks to Dr Jeffrey Priest, Harvey Skinner and Ken Yeates. I’d also like to thank all the general staff that I have come into contact with within the School of Civil Engineering who have made my stay here very enjoyable. Professor William Powrie has been very diligent in reading through drafts of this report and other interim reports that I have provided him with. His comments and insights have been enormously beneficial. Last but not least, I acknowledge the continual support of my parents, Sylvia and Patrick Le Pen, and my wife, Lisa Bernasek. i UNIVERSITY OF SOUTHAMPTON FACULTY OF ENGINEERING, SCIENCE AND MATHEMATICS SCHOOL OF CIVIL ENGINEERING AND THE ENVIRONMENT PHD THESIS TRACK STABILITY ABSTRACT The aim of this research is to develop a fuller understanding of the mechanical behaviour of the sleeper/ballast interface, related in particular, to the forces applied by high speed tilting trains on low radius curves. The research has used literature review, field measurements, and laboratory experiments on a single sleeper bay of track. Theoretical calculations are also presented. Field measurements are carried out using geophones to record time/deflection for sleepers during passage of Pendolino trains on the West Coast Main Line. Calculations are presented to quantify normal and extreme magnitudes of vertical, horizontal and moment (VHM) loads on individual sleepers. Results from laboratory experiments, on the pre-failure behaviour of the sleeper to ballast base contact area, show that lateral load/deflection behaviour is load path dependent and relations are determined for improved computer modelling of the sleeper/ballast interface. Further test results are used to establish the failure envelopes for combined VHM loading of the sleeper/ballast base contact area. Tests show that the sleeper/ballast base resistance at failure occurs at a load ratio (H/V) of about 0.45 (24°) at 2 mm of displacement tending to 0.57 (30°) at greater displacements. In addition, measurements from pressure plates within the testing apparatus are used to describe the development of confining stress within the ballast during 100 cycles of vertical load. The development of confining stress is assessed with reference to a finite element model of the laboratory apparatus and it is shown that the earth pressure ratio moves towards the active condition for peak load and the passive condition at minimum load per cycle. The contribution to lateral resistance of the crib ballast and varying sizes of shoulder ballast is also established and it is found that the shoulder and crib resistance can best be characterised by taking the mean resistance over a range of deflection from 2 mm to 20 mm. Calculations are presented, supported by the experimental data, to quantify the resistance from different sizes of shoulder ballast and a chart is presented which can be used as the basis for shoulder specification in practice. ii ABBREVIATIONS BOEF Beam On Elastic Foundation BS British Standard CTRL Channel Tunnel Rail Link (recently renamed to HS1; High Speed 1) CWR Continuously Welded Rail DFT Department For Transport DSSS Dynamic Sleeper Support Stiffness DTS Dynamic Track Stabilization ERRI European Rail Research Institute FTSM Flexible Track System Model FWD Falling Weight Deflectometer LVDT Linearly Variable Displacement Transducer MGT Mega Tonnes of Traffic NR Network Rail RGS Railway Group Standard TGV Train de Grand Vitesse UIC Union International des Chemins de fer VHM Vertical, Horizontal, Moment SPECIALIST TERMS Cant For the purposes of this document, cant is expressed as the design difference in level, measured in millimetres, between rail head centres (generally taken to be 1500 mm apart) of a curved track (compare with ‘cross level’). (Rail Safety and Standards Board GC/RT5021, 2003) Cant deficiency The difference between actual cant and the theoretical cant that would have to be applied to maintain the resultant of the weight of the vehicle and the effect of centrifugal force, at a nominated speed, such that it is perpendicular to the plane of the rails. For the purposes of this document, cant deficiency is always the cant deficiency at the rail head, not that experienced within the body of a vehicle. (Rail Safety and Standards Board GC/RT5021, 2003) Maximum The maximum cant deficiency at which a train is designed to travel. For conventional design service trains a cant deficiency of 6° is specified, for tilting trains this is increased to cant deficiency 12°(Railway Safety GC/RC5521, 2001) Curving force Centrifugal force horizontal to the Earth's surface Dynamic load Vertically any load effect above the static load of a train resting on the tracks and horizontally any load above the wind load and when curving the centrifugal force load. Dynamic The peak load divided by the peak deflection of the underside of a rail seat area of an Sleeper unclipped sleeper subjected to an approximately sinusoidal pulse load at each rail seat; Support the pulse load being representative in magnitude and duration of the passage of a heavy Stiffness axle load at high speed. (DSSS) Lateral The direction across the track whether horizontal or canted Sleeper/ballast All contact areas between the sleeper and ballast including base, shoulder and crib interface Track modulus Spring support constant, always evaluated for a single wheel load on half the track. (k) Trackbed Soil layers below the sleeper base iii Track Rails, railpads, sleepers. superstructure Track Similar to the trackbed, soil layers supporting the superstructure. substructure Track system Refers to the rails, pads, sleepers and trackbed Low radius Referring to curves where the curving force approaches and reaches the peak curves permitted. A lower limit for the radius of curves in this category can be taken from Railway Group Standards. These state that the maximum design limiting cant deficiency of 300 mm for a Pendolino is reduced on curves less than 700 m in radius (Rail Safety and Standards Board GC/RT5021, 2003). The upper limit depends on the operating cant deficiency of the train and the cant of the track. For a train travelling at 110 mph on 150 mm canted track the maximum radius of curve at which the vehicle can maintain an operating cant deficiency of 300 mm is 760 m. In reality few curves are of such low radius and curves evaluated on the WCML for this research had radii of 1025 m and 1230 m with 150 mm cant present. The phrase low radius curve will therefore be interpreted to incorporate curves in the range 700 m to 1230 m in this report. DEFINITION OF SYMBOLS USED a 1. Sleeper spacing 2. Speed of sound in fluid a Angle of cant of the track b 1. Exponent 2. Sleeper width at base B Sleeper length CF Dimensionless constant for wind loading CL Dimensionless constant for lifting wind load CS Dimensionless constant for sideways wind load CR Dimensionless constant for rollover wind load d Frictional resistance angle at interfaces (e.g. ballast to sleeper) r Density D Shear force d Distance between railheads centre to centre Ddegrees Operating cant deficiency in degrees eN Strain in the ballast layer after N cycles of load e1 Strain in the ballast layer after cycle 1 e Eccentricity E Young's modulus EI Bending stiffness of the rail Er Stress state dependent vertical modulus (used by Geotrack) f Internal friction angle F Force/Force on body moving through fluid medium g Bulk unit weight h 1. Reference height 2. Height of sleeper H Horizontal (load) I Second moment of area Hg Height of centre of gravity above rail on level track k Foundation coefficient (N/m/m) (also referred to as track modulus) K Earth pressure ratio k1 to k4 Experimental constants Ka Active earth pressure coefficient` iv K0 Normally consolidated earth pressure coefficient` Kp Passive earth pressure coefficient` l Angle of heaped ballast L 1.