Definition and Role of Rail Spikes in Track Structure
Rail spikes, commonly known as dog spikes or cut spikes, are driven through the rail foot, or through a baseplate and into the sleeper, to hold the rail in position. Alongside screw spikes, they are among the oldest forms of rail fastening and are still widely used on timber-sleeper and composite-sleeper lines, industrial sidings, mining tracks and crane rails. The spike is not simply a clamp: it interacts with the rail foot, the baseplate and the sleeper to transfer wheel loads, resist lateral displacement, control gauge and oppose longitudinal rail movement under repeated traffic.
How Spikes Transfer Loads to the Sleeper
When a wheel passes over a spiked joint or a spiked section of track, the vertical load is carried by the rail web and foot into the sleeper seat, with the spike shank acting mainly in shear through the holes in the rail foot or baseplate. The more demanding interactions are horizontal. On a curve, flange force pushes the rail outward; the shoulder of the spike shank bears against the edge of the rail foot hole and transmits that lateral force into the sleeper. Where the rail is held directly by spikes without a baseplate, the same mechanism resists gauge widening. At the same time, rail creep from braking and acceleration generates longitudinal forces that the spikes resist through friction and bearing at the foot edge. A correctly driven spike therefore works as a small structural connection, not just a positioning pin.
Dog Spikes versus Screw Spikes
The two families of spike differ in how they generate holding force. A dog spike relies on elastic friction between its tapered shank and the compressed timber fibres around the hole. A screw spike has a threaded shank that engages the sleeper over a longer length, giving higher withdrawal resistance, especially in softer or composite sleepers, and allowing controlled removal and re-installation. The table below compares the key behaviours a buyer should consider.
| Property | Dog spike (cut spike) | Screw spike |
|---|---|---|
| Holding mechanism | Friction against timber fibres | Thread engagement in sleeper |
| Withdrawal resistance | Moderate; depends on timber density and moisture | Higher; less sensitive to timber condition |
| Installation | Hammer or spike driver, no pre-boring normally needed | Pre-bored pilot hole plus torque-controlled driving |
| Removal and reuse | Damages surrounding timber when pulled | Clean removal; re-drive possible |
| Typical application | Timber sleepers, industrial sidings, temporary track | Timber and composite sleepers, switch zones, bridges |
Installation Conditions That Control Spike Performance
Spike behaviour is decided as much by installation as by the spike itself. In timber sleepers, the holding power of a dog spike rises with timber density and falls sharply when moisture content is high; a spike driven into wet or decayed timber can lose most of its resistance within a season. Pre-boring a pilot hole of about 80 percent of the shank diameter reduces splitting in hard timber while still allowing the fibres to grip. Screw spikes must be driven with a calibrated torque wrench or torque-limited driver, because over-tightening strips the thread in softwood sleepers and under-tightening leaves the rail free to lift. On track, the spike should sit square to the sleeper surface; a spike driven at an angle pulls sideways during service and accelerates hole enlargement. Where baseplates are used, the spike length must suit the combined thickness of rail foot, pad and baseplate so that full shank engagement is achieved.
Inspection and Maintenance of Spiked Fastenings
Spiked track needs regular visual inspection because spikes loosen progressively rather than failing suddenly. Common defects include raised heads, corrosion at the rail foot seat, hole enlargement from pumping under heavy traffic, and sideways tilt caused by lateral forces on curves. Gauge widening beyond tolerance is the clearest sign that spikes have lost their grip and that re-driving or replacement is due. On timber sleepers, a loose spike should not simply be hammered deeper; the hole should be re-gauged and, where necessary, a larger-diameter or screw-type spike fitted, or the sleeper renewed if the timber is decayed. Torque checks on screw spikes should follow the values set by the fastening supplier or the track standard in force, and re-tightening should be scheduled after the first weeks of traffic, when initial settlement has occurred.
Frequently Asked Questions
What is the difference between a dog spike and a screw spike?
A dog spike is a plain tapered pin held by friction in the sleeper, while a screw spike has a threaded shank that engages the sleeper material, giving higher withdrawal resistance and cleaner removal.
How much holding force does a rail spike provide?
Holding force varies widely with sleeper material, moisture content, hole preparation and spike size, so no single figure is meaningful. In practice, screw spikes on sound timber or composite sleepers hold substantially more than dog spikes under the same conditions.
Why do spikes loosen under traffic?
Repeated wheel loads pump the spike in its hole, timber fibres crush and dry out, and corrosion reduces the effective shank section. Loosening is accelerated on curves and at joints where lateral and impact forces are highest.
Can spikes be used on concrete sleepers?
Concrete sleepers require pre-cast inserts or plastic dowels; plain spikes cannot grip concrete. Where steel or plastic dowels are installed, screw spikes are normally used rather than dog spikes.
How does spike corrosion affect the track?
Corrosion at the rail foot seat reduces the effective shank section and the clamping force, increases gauge widening risk, and can discolour and pit the rail foot, which then requires grinding or rail replacement.
What torque should be applied when installing screw spikes?
The correct torque depends on spike diameter, sleeper material and the dowel or insert used. Always follow the fastening supplier's specification; the track standard in force should be treated as the minimum requirement.