Introduction. Effect of Confining Pressure on Particle Degradation. Ballast Breakage and Impact Loads. Ballast Fouling and Improvement using Geogrids

Transcription

1 Second International Conference on Transportation Geotechnics 1-12 September 212 Hokkaido University, Sapporo, JAPAN Contents Performance Evaluation of Shock Mats and Synthetic Grids in the Improvement of Rail Ballast Prof. Buddhima Indraratna Professor of Civil Engineering & Research Director, Centre for Geomechanics and Railway engineering ARC Centre of Excellence in Geotechnical Sciences and Engineering University of Wollongong, NSW 2522 Australia Introduction Effect of Confining Pressure on Particle Degradation Ballast Breakage and Impact Loads Ballast Fouling and Improvement using Geogrids From Theory to Practice: Bulli and Singleton Tracks Sanjay Nimbalkar Research Fellow, ARC Centre of Excellence, Centre for Geomechanics and Railway engineering University of Wollongong, NSW 2522 Australia Cholachat Rujikiatkamjorn Senior Lecturer, School of Civil, Mining & Environmental Engineering Centre for Geomechanics and Railway engineering University of Wollongong, NSW 2522 Australia Finite Element Analyses of Rail Tracks Conclusions Problems in Rail Track Substructure Large-scale Cyclic Triaxial Rigs Built at UoW Ballast Crushing Foundation soil liquefaction Poor Drainage Coal fouling Differential settlement Suiker, 22 Queensland Flooding Track Buckling Prismoidal Triaxial Rig to Simulate a Track Section (Specimen: 8x6x6 mm) Cylindrical Triaxial Equipment Cylindrical Triaxial Equipment (Specimen: 3 mm dia.x6 mm high)

2 Effect of Confining Pressure on Strain Behaviour of Ballast Indraratna, Lackenby and Christie (25), Geotechnique n (%) Volum metric Strai Friction angl le, (degree) Monotonic Loading kpa 8 kpa 15 kpa 3 kpa 6 kpa 9 kpa 12 kpa 24 kpa dilation compression Axial Strain (%) Peak friction i angle, p, of fresh ballast Dilatancy (+) Particle breakage (-) Compression f (excludes particle breakage and dilatancy) Effective confining pressure (kpa) Volum metric Strain (%) Friction Angle ( ) Cyclic Loading q max = 5 kpa 3 kpa 1 kpa 2 kpa 3 kpa 45 kpa dilation compression 3 6 kpa 9 kpa 12 kpa 18 kpa 24 kpa Axial Strain (%) p Dilation fb (includes breakage but excludes dilatancy) Compression f (excludes particle breakage and dilatancy) Confining Pressure (kpa) Increasing Confining Pressure using: Intermittent Lateral Restraints or Embedded Winged Sleepers Intermittent lateral restraints Lateral restraints Winged sleepers 1 Fractio on Passin ng Effect of Confining Pressure on Particle Degradation (Cyclic Loading) A B BBI A A B PSD = particle size distribution 2.36 = smallest sieve size d 95i = d 95 of largest sieve size Arbitrary boundary of maximum m breakage d 95i Shift in PSD caused by degradation Initial PSD d max Final PSD 2.36 Sieve Size (mm) 63 Ballast Breakage Index (BBI) Indraratna, Lackenby and Christie i (25) Geotechnique, ICE, UK. Vol. 55(4), Ballast Bre eakage Inde ex, BBI ne e Dilation Zon Unstable Optim mum Degr radation Zone Optimum Contact (I) (II) (III) q max = 5 kpa q max = 23 kpa Compressive Stable Degradation Zone Effective Confining Pressure (kpa) Constitutive Modelling of Particle Breakage Before Loading Voids Asperity wear After Loading New hairline micro-cracks Ballast Broken particles fill voids (fouling) Sharp corners broken off Rail Sleepers Lackenby, Indraratna, McDowell and Christie (27) Geotechnique, ICE, UK. Vol. 57(6), Decreased Drainage Decreased Shear Strength

3 Model validation Track Modelling Incorporating Ballast Breakage Energy Approach Salim & Indraratna (24) Canadian Geotechnical Journal Journal, 41: d v 2 1 tan 45 f 1 deb / d 1 1 sin f 2 d 1 q p 2 1 d v d tan 45 f p 1 v tan 2 45 f d d kpa kp Dilation kpa kpa d vp B 9 M 9 3 M 2 * M p 3 kpa Contraction Distrortional strain, s (%) Deviatoric Strain, εs (%) M * 9 3 M 2 * M Model M d l Parameters P t need d to t be determined by largescale testing Recommended New Railway Ballast Grading Ballast Breakage Index (BBI) Without shock mat Stiff -.17 Soft -.8 Stiff Above ballast.145 Stiff Below ballast.129 Stiff Above & below ballast.91 Soft Above ballast.55 Soft Below ballast.56 Soft Above & below ballast.28 1 With Shock mat Recommended Grading %P Passing g 8 Australian Standards (AS ) 6 Cu = Cu = Shock Mat 1 Nimbalkar, Indraratna, Dash & Christie (212). JGGE, ASCE, 138(3): Volume Change Behaviour p p 1 o ( i ) 9 3 M 2 * M d 2 p p cs ( i ) cs 2 po B 1 9 M * M * M 2 1 e i p p Effect of High Impact Loads and Track Degradation Location of shock mat 1 1. Deviatoric Strain, εs (%) Distrortional strain, s (%) 3 = 5 kpa Model prediction -4. Stress-Strain behaviour d sp Subgrade type v (%) 1 kpa Indraratna and Salim (22) g g, Geotechnical Engineering, ICE Proceedings, UK. f = basic friction angle 2 kpa kp 8 d sp q = Distortional / deviator stress 3 = 3 kpa 6. Conventional theory p = Effective mean stress Model prediction 16 Test data for crushed basalt ((Indraratna and Salim 21)) -6. Vo lumetric stra ain, Disstortional strress, q (kpa a) deb = increment of energy consumption due to particle breakage -8. Test data for crushed basalt (Indraratna and Salim 21) 2 1 Particle size (mm) 1 12

4 Role of Ballast Fouling on Track Performance Infiltration of coal Fouling Index (FI) Selig and Waters (1994) FI = P P.75 Ballast Fouling Assessment P 4.75 = Percentage (by weight) passing the 4.75 mm sieve P.75 = Percentage (by weight) passing the mm sieve Fouling Index, % F coal-fouled ballast sand-fouled ballast clay-fouled ballast Slurried Clay infiltration Percentage Void Contamination (PVC) Feldman and Nissen (22) V f PVC = V vb 1 V vf = Total volume of fouling material passing 9.5 mm sieve V vb = Initial voids volume of clean ballast PVC, % Void Contaminant Index (VCI) proposed by UOW VCI = (1+e f) e e b G s.b G s.f M f M 1 M b e b = Void ratio of clean ballast e f = Void ratio of fouling material G s-b = Specific gravity of clean ballast G s-f = Specific gravity of fouling M b = Dry mass of clean ballast = Dry mass of fouling material M f Void Contaminant Index (VCI) proposed p by UOW 4 VCI = (1+e f) e e b G s.b G G s.f M f M 1 M b VCI, % Percentage fouling, % Impeded Drainage of Track due to Ballast Fouling Improvement of Fouled Ballast behaviour with Geogrids 1 Coal-fouled ballast: Experimental /s) tivity, k (m/ Hydrau ulic Conduct 1-1 Coal-fouled ballast: Theoretical Sand-fouled ballast: Experimental Sand-fouled dballast: Theoretical Bellambi Site VCI=33% Rockhampton Site VCI=72% 1-4 hydraulic conductivity 1-5 of coal fines Sydenham Site VCI=22% hydraulic conductivity of clayey fine sand Void Contaminant Index, VCI (%) Large-scale permeability test apparatus Hydraulic Conductivity (k) of fouled ballast k k b f k k VCI (k k ) f 1 b f Variation of hydraulic conductivity vs. Void Contaminant Index Tennakoon, Indraratna, Cholachat h & Nimbalkar (211) ASTM Geotechnical Testing Journal. k b = Hydraulic conductivity of clean ballast k f = Hydraulic conductivity of fouling material Large-scale direct shear test apparatus

5 Modelling Geogrid-reinforced reinforced Fouled Ballast under Shearing Loads Use of geogrid for improving fouled ballasted track Indraratna et al. (211). Geotextiles & Geomembranes, 29: Noma alised pea ak shear stress, p n 25 n = 15kPa 2.5 Without geogrid With geogrid n = 27kPa Maintenance n = 51kPa n =75kPa p n stress, Nom malised pe eak shear rapid reduction Convergence App p ) Ap e) e VCI (%) VCI (%) Computer modeling using discrete element method Beyond a VCI of 7%, the shear strength approaches that of fouling material itself. Optimum Geogrid Aperture Size Indraratna et al. (211). ASTM Geotechnical Testing Journal, 35 (2): 1-8 From Theory to Practice: Geosynthetics in Bulli Track Geogrids Used for Testing Geogrid type Aperture shape Aperture size (mm) T ult (kn/m) G1 Square Unreinforced G2 Triangle G3 Square G4 Rectangle Optimum A/D 5 Min.A/D 5 Max.A/D 5 Details of instrumented track G5 Rectangle G6 Square G7 Rectangle A/D5 The minimum and maximum aperture sizes of geogrid required to optimize the shear strength th are.95d 5 and 2.5D 5 respectively. The optimum aperture size of geogrid can be treated as D 5 Section of ballasted track bed with geocomposite layer

6 Field Trial on Instrumented Track near Wollongong Field Instrumentation - Bulli Geocomposite layer (geogrid+geotextile) Ballast placement over before ballast placement the geocomposite 8 October 26 Geotextile Recycled Ballast from Chullora Quarry, Sydney Fresh Ballast Bombo Quarry, Wollongong Bonded Geogrid Settlement pegs Displacement installed at ballastcapping transducers installed at interface sleeper-ballast interface Deformation Response of Ballast at Bulli Track Indraratna et al. (21). JGGE, ASCE, 136(7): Use of Shock Mats & Geogrids: Singleton Track (NSW) v ) avg (mm) eformation of ballast, (S v Averag ge vertical de Number of load cycles, N 1x1 5 2x1 5 3x1 5 4x1 5 5x1 5 6x1 5 7x1 5 8x1 5 9x Fresh Ballast (uniformly graded) Recycled Ballast (broadly yg graded) Fresh Ballast with Geocomposite Recycled Ballast with Geocomposite time, t (months) g (%) al strain of ballast, ( 1 ) avg erage vertica Ave Geogrid layer placed above the capping Settlement pegs placement in the track The recycled ballast performed well, and this is because, it was broadly graded compared to the relatively uniformly graded fresh ballast. Mudies Creek Bridge pressure cells installation Placing of shock mat on bridge deck, Feb. 21

7 Use of Shock Mats & Geogrids in Practice: Singleton (NSW) Vertical Deformation of Ballast Layer Use of geosynthetics ) last (mm) Vertical De eformatio on of Ball Time (days) x1 4 1.x x1 5 2.x x1 5 Number of Load Cycles t (%) Vertica al Strain of Ballast Silty-clay Deposit Ballast Ballast with Geogrid Hard Rock Ballast Ballast with Geogrid Bridge Ballast with Shock Mat Geogrids can decrease ballast deformations by as much as 3%. Use of Shock mat above bridge deck Effectiveness of reinforcement increases on softer subgrades. Finite Element Analysis of Bulli Track: 2D Plane Strain Track transverse section deformation (kpa) '- ' Stress, q = Deviator 1 ' Effective confining pressure 3 = 5 kpa E 5 1 asymptote Axial Strain, a (%)

8 Track longitudinal section deformation Settlem ent (m) 5.5 Class A Prediction of Rail Embankment with Cyclic Loading Indraratna et al. (21) JGGE, ASCE, 136(5): Very Soft Alluvial Clay Soft Silty Clay Field Data Prediction-Class A Time (days) xcess pore pressure (kp Pa) Ex Depth (m m) No PVD With 1.5m spacing Time (days) Lateral displacement (m) Field Reduction in lateral displacement -16 No PVD 1.5m spacing Conclusions Provision of sufficient lateral confining pressure improves track performance and reduces the cost of maintenance. Geosynthetics can increase the track confining pressure to reduce particle movement at high train speeds. The optimum aperture size of geogrid can be treated as D 5. Geogrids could decrease ballast deformations by as much as 3%. Shock mats can mitigate ballast degradation under impact loads. The field trials near Wollongong and Newcastle demonstrate the implications of track deterioration, and the advantages of track modernization using synthetic inclusions. Australian Research Council (ARC) Acknowledgment Centre for Geomechanics and Railway Engineering, University of Wollongong, Australia Cooperative Research Centre (CRC) for Rail Innovation Past and Present research students, Research Associates and Technical Staff Industry Organisations: RailCorp (NSW), ARTC, QLD Rail, ARUP, Coffey Geotechnics, Douglas Partners. Thank You!