TRACK TECHNOLOGY
TRACK21: Railway track for the 21st century
T RACK21 is a collaborative research programme grant funded by the UK
Engineering and Physical Sciences Research Council (EPSRC) that aims to improve how existing railway track is maintained and how new lines are designed and built.
The grant brings together researchers from the Universities of Southampton, Birmingham and Nottingham and industry partners including Network Rail, HS2, LUL, RSSB, Balfour Beatty, Tata and Pandrol.
The key research challenge addressed by TRACK21 is to develop improved understandings of the complex mechanisms of railway track behaviour governing stiffness, robustness, longevity, noise and vibration. The goal is to reduce deterioration rates and maintenance requirements substantially, while at the same time mitigating the environmental impacts of noise, vibration and materials use. These are perhaps the most significant challenges facing railway systems today. If successful, the research will lead to reduced costs and improved reliability, with resulting environmental and customer service benefits.
Work over the first 30 months of the grant has focused on developing a better understanding of the way track behaves in response to the increasing demands of heavier, faster and more frequent trains through a combination of field monitoring, laboratory testing and particle scale numerical modelling. A summary of progress in selected areas is given below.
Ballast migration
Figure 1 shows the phenomenon of ballast migration. This may occur on canted curved track traversed by high speed (~200 km/hour) trains, and inv olv es the gradual migration of the ballast down the cant so that the high end of the sleeper
Below: Figure 1 Ballast migra- tion (from Priest et al, 2012)
152 | rail technology magazine Apr/May 13
is exposed and the ballast gathers in a heap against the low rail.
A mechanism has been proposed to explain this behaviour, and is described in full in a paper soon to be published in the Journal of Rail and Rapid Transit (Priest et al, 2012).
Transition zones
Transition zones, where the track passes from ordinary ground onto a rigid substructure such as a bridge or a culvert, are potentially problematic in terms of ongoing differential displacement and increased maintenance requirements.
The strategies adopted to
try to mitigate these effects are sometimes spectacularly unsuccessful (e.g. Coelho et al, 2011) and further research into more effective designs is required.
Within TRACK21, critical zones (including switches, transitions and underbridges) have been identified at various locations mainly on the southern region of the UK network, and their performance is being monitored both from the track and using on-train instrumentation developed at the University of Birmingham.
Earthworks in cyclic loading
Seasonal cyclic shrinkage and swelling of clay embankments resulting from vegetation and climate effects can make it difficult for rail infrastructure owners to maintain the required track geometry. Fatigue might also lead to the gradual failure of such embankments over several decades.
These issues are being investigated in cyclic triaxial
tests in which 70mm diameter
specimens of Lias Clay embankment fill from a site near Bristol are being subjected to cyclic variations in pore water pressure of 100kPa with the total stress held constant. Further tests are being carried out in which the total stresses are being cycled at a much higher frequency, mimicking train passage.
In both cases, the laboratory tests are being complemented by field and full scale studies. Additional collaborators include Mott
MacDonald, GeoObservations and Arup.
Effects of principal stress rotation on different types of track sub-grade
A torsional hollow cylinder apparatus has been set up and a testing procedure developed, following Powrie et al (2007), to investigate the effect of the principal stress rotation associated with train passage on a variety of railway foundation soil types. Particular emphasis is being placed on the effect of clay content and the time interval between loading events.
Current data suggest a reduction in the susceptibility of a sub-base material with increasing clay content, up to a clay content of about 16%. Above this, the reduced permeability starts to have an adverse effect.
The effectiveness of ballast and sleeper modifications
The replacement of traditional timber sleepers by reinforced concrete has resulted in a much harder interface, with smaller and possibly fewer sleeper to ballast contacts and the increased likelihood of ballast particle breakage rather than embedment into the softer sleeper material.
The University of Southampton sleeper testing rig (figure 2; Le Pen and Powrie, 2011) has been upgraded to enable the long-term performance of different combinations of sleeper material (timber, plastic, steel) and shape (traditional, duo-bloc, inverted U) to be investigated; and also the effectiveness of under sleeper pads in reducing sleeper/ballast contact forces.
Below: Figure 2 University of Southampton ballast and sleeper testing rig
Professor William Powrie FREng, principal investigator of TRACK21 at the University of Southampton, describes the latest track research and its implications for the industry.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216 |
Page 217 |
Page 218 |
Page 219 |
Page 220 |
Page 221 |
Page 222 |
Page 223 |
Page 224 |
Page 225 |
Page 226 |
Page 227 |
Page 228 |
Page 229 |
Page 230 |
Page 231 |
Page 232 |
Page 233 |
Page 234 |
Page 235 |
Page 236 |
Page 237 |
Page 238 |
Page 239 |
Page 240 |
Page 241 |
Page 242 |
Page 243 |
Page 244