OPPORTUNITIES for track maintenance on mass transit railways can be limited, and high passenger volumes make any disruption to services extremely costly. For these situations Pandrol has developed its Double Fastclip rail fastening. This has been installed on Singapore’s North East Line, which is expected to open this month (MR03 p20). Part of the VIPA family of double-resilience baseplate track supports, DFC eliminates all bolts and threaded elements and also offers double electrical insulation.

A first set of fastenings is incorporated directly into the concrete sleeper to hold the baseplate in position. A second set of Fastclips attached to the baseplate then secures the rail in the conventional way. Releasing the top fastenings allows the rail pads to be replaced without the need to remove the baseplate. Stiffness of the fastening can be altered by changing the combination of baseplate and pad.

The ease of disassembly and reassembly will speed maintenance, although DFC is designed to minimise the need for maintenance from the outset. All the components are visible, offering the possibility of automated video inspection. NEL operator SBS Transit has acquired a multi-function maintenance vehicle which will be able to inspect the track at full line speed between service trains.

DFC is particularly suited for use with slab track. Preassembled sleepers and rails can be aligned into panels using top-down techniques, and secured by mass-pour concrete. This method of construction does not require large amounts of adjustability in the fastening.

Double Fastclips were first used for concrete-bearer turnouts on the Gardermoen airport line in Norway. From these, a highly-resilient design was developed for Singapore MRT’s Changi Airport branch and subsequently NEL. Practical evaluation of the design on a short length of line near SMRT’s Orchard station in 1998 confirmed the laboratory assessments of track integrity and vibration isolation performance.

The principle measure of resilience is vertical stiffness. Laboratory tests verified the static vertical stiffness for the basic assembly at around 20MN/m, the value required by SMRT to match the original track specifications. However, subsequent testing in service found that under operational conditions the dynamic stiffness - which determines the effectiveness of the vibration isolation - is 30% lower than on the original track.

On conventional track the baseplate is held in place on a very resilient pad by anchor studs. As the pad compresses under passing trains, the baseplate slides down the studs, but any off-centre loading causes binding, effectively increasing the stiffness. In common with other VIPA designs, DFC allows the baseplate to move freely, eliminating any binding.

NEL is using two versions of DFC - with and without adjustability. The adjustable fastenings are designed to allow matching of worn and new rails during emergency replacement.

CAPTION: Pandrol Double Fastclip rail fastenings are used on Singapore’s North East Line

Pandrol Rail Fastenings, UK Reader Enquiry Number 138