The Fastening System in Concrete Sleeper Track
Concrete sleepers have become the default choice for mainline track because of their high strength, stable geometry and long service life, but their rigidity makes the fastening system more important than it is on timber. Concrete cannot absorb impact by local deformation, so every vertical and lateral load passes through the fastening assembly before it reaches the sleeper. The fastener therefore has to hold the rail foot down with a controlled clamping force, keep gauge and inclination within tolerance, and at the same time insulate the rail from the reinforcement inside the sleeper so that track circuit current cannot leak away.
Because these duties are constant, the practical differences between fastening systems lie in how the clamping force is generated, how much adjustment is available, and how much maintenance each design demands over its life.
Spring Clip Systems: Type I and Type II
The spring clip family is the most widely used group of fastenings on concrete sleeper track. The type I fastening consists of an omega-shaped spring clip, spiral spikes, a gauge baffle, a baffle seat and an elastic rubber pad. It is well damped and holds the track geometry effectively, but its clamping force is limited and its elastic range is small, while the clip itself carries a modest safety reserve of strength. These characteristics make it suitable for light and medium duty rather than heavy-haul operation.
The type II fastening follows a similar architecture with an upgraded clip material: 60Si2CrVA spring steel to GB/T 1222 replaces the lower-grade clip of type I. The result is a higher clamping force, a larger safety reserve of strength and a small residual deformation after repeated loading, which suits 60 kg/m rail laid on type II or type III concrete sleepers. The trade-off is that anti-corrosion and anti-loosening work becomes more demanding, and the design is not intended for high-speed lines.
Spring Clip Systems: Type III, Type IV and Type V
The type III fastening is a boltless, shoulder-free design built from an e-shaped spring clip, an embedded iron seat, an insulating gauge block and a rubber pad. It develops high clamping force with good elasticity and strong gauge-holding ability while requiring little maintenance, and it represents the direction that boltless fastenings have taken. Its limits are that the height cannot be raised after installation, the gauge block is easily damaged on small-radius curves, and clamping force falls after repeated re-use of the clip.
Two further variants extend the family. The type IV fastening is intended for high-speed ballasted track, with an optimised clip structure that allows more precise gauge adjustment. The type V fastening starts from the type II design and increases both the elastic range of the clip and the clamping force it delivers, again for high-speed ballasted track. Both depend on consistent sleeper shoulder geometry and on tight control of installation clamping force to realise their design performance.
Clip Plate Fastening Systems
A second group uses a clip plate rather than a spring clip as the retaining element. The assembly consists of clip plates, threaded spikes, spring washers, iron seats and buffer pads. The threaded spikes are anchored in the reserved holes of the concrete sleeper support platform, traditionally with cement mortar, and the clip plates are then drawn down with bolts to trap the rail foot. KPO fastening systems are a well-known example of this group.
The structure is simple and economical, and it is easy to inspect in service. Its limitation is elasticity: compared with a spring clip fastening, the clip plate offers a smaller elastic travel and generally a lower clamping force, so it is used where impact loads are moderate. A further variant relies on a plate-like clip that develops clamping force through bending deformation only; because it cannot use both bending and torsional deformation, its elastic behaviour is poorer than that of an omega-shaped or e-shaped clip, and its range of application is correspondingly narrower.
Comparison of Common Fastening Types
| Fastening type | Clamping element | Typical application |
|---|---|---|
| Type I spring clip | Omega-shaped spring clip with spiral spike | Light and medium duty mainline track |
| Type II spring clip | 60Si2CrVA spring clip to GB/T 1222 | 60 kg/m rail on type II or type III sleepers |
| Type III spring clip | E-shaped spring clip, boltless and shoulder-free | Low-maintenance track, care needed on small radius curves |
| Type IV spring clip | Optimised spring clip | High-speed ballasted track |
| Type V spring clip | Wider-range, higher-force spring clip | High-speed ballasted track |
| Clip plate system | Clip plate with threaded spike | Economical track with moderate impact loading |
Frequently Asked Questions
Q: Which fastening system is used most widely on concrete sleeper track?
Spring clip systems are the most common group, because they combine a reliable clamping force with tolerance of the small elastic movements that concrete sleeper track demands.
Q: Why does the type II fastening use 60Si2CrVA steel?
The higher-grade spring steel raises clamping force and strength reserve while keeping residual deformation small after repeated loading, which allows it to serve 60 kg/m rail on heavy mainline track.
Q: What is the main advantage of a boltless fastening?
It removes the bolted connection and its loosening risk, so it holds gauge well and needs less routine retightening, at the price of reduced height adjustment after installation.
Q: Why are rubber pads used in every system described here?
The pad buffers impact between rail and sleeper and provides electrical insulation for the track circuit, protecting both the sleeper and the fastening components.
Q: When is a clip plate system preferred over a spring clip system?
When the loading is moderate and cost or simplicity of assembly dominates, since the clip plate solution is economical to make and easy to inspect in service.
Q: What limits the service life of a fastening on concrete sleepers?
Loss of clamping force through clip fatigue and relaxation, ageing of the rubber pad, and damage to insulating and gauge components, particularly on small radius curves.