Some FAQ’s for using LR55 tracks on main line railways
by Lewis Lesley
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Maximum line speed
Maximum axle weight of rail traffic
Limits on radius of curvature of the railway
Limits on track cant
Ground bearing pressures
Load bearing requirement of formation
Drainage arrangements
Transition arrangements to adjacent track system
Electrical performance
Handling and setting of trough beams
Rail section – compatibility with UK wheel profiles
Proving initial rail integrity
Welding of the rail strings
Handling the rail
Lining and levelling of rail
Use of grout system – include manufacturers documentation
Inspection requirements
Rail wear limits
Rail repair techniques
Ultrasonic rail testing
Rail replacement
We have only been able to test with trains at up to 50mph. Theoretically LR55 should be more stable than sleepered tracks, and therefore capable of 200mph speeds. Some Civil Engineering students in Liverpool did a study using LR55 for high speed railway stations, with trains passing at 200mph.
LR55 has been tested without failure up the the maximum of the University Structures lab in Liverpool,. viz 80tonnes axle loadings. All FEA and cyclic lab tests (200 million cycles) have been at 25tonnes.
The LR55 has been curved down to 15m radius. Under 50m radius, LR55 has to be factory bent There are few main line railway applications which would need such tight radii. Above that in long welded strings, LR55 will curve like UIC60
LR55 can be canted to the present and anticipated cant deficiency levels over the next 20 years.
For 25tonne axle loads, the max. ground pressure is 250MPa (immediately below the axle) and falls to a slight hog 2m away either side. We have also looked at the impact of 2 axles (in a bogie with 2m wheelbase) each with 25tonnes. The max. pressure does not increase but the foot print is longer. All lab tests of the LR55 track were on dry sand.
This depends on the maximum weight of passing trains, since the track mass is several orders of magnitude less than eg.loaded freight trains. Because the LR55 attenuates ground borne vibrations (under 20Hz) by 30dBA, from the mass-spring-mass-spring interaction, the peak loading into the formation is reduced, marginally.
The Type One Highway base would be specified for a given design life, and annual tonnage, which will give a required thickness dependent upon the CBR of the sub soil. This is guarantee that the LR55 trough and base layer remain elastic throughout the operational life.
LR55 tracks are laid on a compacted highway type 1 base, and then surrounded by conventional ballast. Drainage should be no more of a problem than with sleepered tracks laid in ballast.
There are designs for transitions between LR55 and all known rail profiles in EU use. These designs are for rails cast in equivalent steel grades to adjacent rails. The 1996 installation in Sheffield, which continues to give maintenance free operation, has transitions with 80lb flat bottom (Vignoles) rails. Both ends of the transition can be welded normally to the adjacent rail.
The LR55 being electrically and mechanically insulated from the concrete pre cast foundation trough gives very low resistivity with respect to earth. The installation in Sheffield was measured as more than 1000 ohm km. While this was measured with a dc current, the impedence to ac current will be similar, since the inductance between rails and parallel structures is low.
In terms of current resistance along the rails, being of a similar cross sectional area, and using the same steel grade will give a similar resistance/impedance as eg. UIC60.
The foundation troughs would be made in 6m or longer lengths, and delivered to site by rail. They would be mechanically unloaded by hiab, or adapted JCB, and can be laid directly on the prepared compacted highway type one base, in a similar manner to say drainage channels, using a datum (string) for line and level. Initially the troughs are mechanically linked to each other by a “hairpin” clip. Once the PU bonding grout has been injected, the end faces of the troughs bond with each other,.
The LR55 flangeway is identical with the EU Ri60 (Phoenix girder rail) flangeway. This has been designed to accommodate all rail wheel profiles operating in the EU.
In the first instance this would be the responsibility of the Steel Mill which rolls the rail, and Network Rail or other railway administration would expect delivered rails to meet the order specification for metallurgical and structural integrity. Sample rails could be independently inspected (eg. at the mill) to ensure the required standard is provided. The concrete pre cast foundation troughs would also be subject to quality control by the concrete caster. Similarly the PU Grout would be warranted by the manufacturer, which since this is a mass produced product would be to a high quality level.
The laying of the rails into tracks, then becomes a installation quality control exercise. Achieving the required final specification will depend on the competence and efficiency of the installation team, and the supervision of the site engineer. One major advantage of the LR55 system, is that achieving the final rail line and level is a two stage process, with a higher tolerance allowable for the foundation troughs, and the rails can be set out and bonded to a very high tolerance.
LR55 rail steel is the same as UIC60, 80lb and other rail profiles. LR55 has been both electrically (flash butt) and thermit welded. The LR55 is slightly stiffer than Vignoles rail in the horizontal plane, and less stiff in the vertical plane. Neither of these should make string welding any more difficult than Vignoles rails. Transporting to site on rail wagons will similarly present no more difficultiy.
The rail flange can be lifted with tongs, as conventional rails are lifted by the rail head, whether manually or mechanically. For strings, the handling procedures would be similar to established practice.
LR55 tracks can be laid one rail at a time. One can provide the datum for the second. The rail is laid in the the pre cast foundation trough using either:
Either method will allow the rail to be adjusted to line and level before the liquid PU Grout is injected underneath the rail, to bond the rail into the trough(s).
ALH (System 6) and SIKA (KC340) are the two PU Grouting systems tested to date. Universal has also indicated that it has an equivalent PU Grout. Documentation will be supplied. KC340 was type approved by Railtrack, so should also be approved by Networkrail ?
These are similar to conventional tracks. Proper drainage is required to maintain the integrity of the formation, and of the trough base. Lab tests with 2m wide wash out/voids, shows that the track will self support whilst still carrying traffic, pending repair. The concrete troughs are very still in both horizontal and vertical planes. Providing the tracks have been installed according to the method statement, effectively the track is a low/no maintenance system. In the nearly 12 years, the Sheffield installation has required no maintenance. There is no need to tamp the LR55 rail to maintain the proper track profile.
The LR55 has been designed for a minimum of at least 5mm vertical rail head wear. The limiting condition is preventing flanges from running along the bottom of the flangeway, and the rail supporting flanges retaining the minimum thickness to provide structure support.
Because the rail is continuously and elastically support, the occurance of hunting will be much less frequent, and therefore there will be less side and head wear, and the much lower probability of the formation of rail head corrugations or gauge corner cracking requiring restorative rail grinding. This in itself will prolong rail life.
For rail head wear, the easiest repair technique is rewelding and grinding back to the required profile. The Sheffield installation after 12 years shows no significant wear, and so should have a life of at least 30 years without any repairing.
Standard ultrasonic testing can be used on the LR55, calibrated for the lesser rail depth.
Replacing the track at the end of its life, will follow the same process as installation, including replacing the type one highway base, which would have been installed initially for the required elastic life of the traffic anticipated.
The concrete troughs being low value components, will be recycled as aggregate, including track ballast at the end of the track life. Similarly the rails can be ( remelted and) rolled as new rails. Various US mills simply reheat and reroll the rail without meltdown. The PU grout will be recycled as granular fill for new PU Grout.
(c) Lewis Lesley
December 2007