The Role of Railroad Spikes in Track
A railroad spike holds the rail foot to the sleeper and prevents lateral movement, rail creep and gauge widening under traffic. Dog spikes are the classic fastening for timber ties: the flattened head bears on the rail foot while the square or rectangular shank is driven into the wood. Screw spikes are threaded and are screwed into timber ties, or into plastic dowels, resin-anchored inserts, or cast-in steel sleeves in concrete sleepers where the higher pull-out resistance is needed. Spikes are still specified for yards, sidings, secondary lines, timber bridges and some switch sections, and they are also used as supplementary fastenings on main lines.
Spike Types and Material Grades
Dog spike (cut spike): driven with a hammer or mechanical driver; available in plain steel, hot-dip galvanized, or alloy steel grades for corrosion resistance.
Screw spike (coach screw): threaded shank with a square or hexagonal head, tightened with a torque wrench or sleeper-drilling machine; higher pull-out resistance than a dog spike.
Mushroom spike and elastic spike: specialized variants used for gauge retention in specific systems.
Common materials are carbon structural steel per GB/T 700 for ordinary spikes and quenched and tempered medium-carbon steel per GB/T 699 or alloy spring steel for high-strength screw spikes. Surface protection is normally hot-dip galvanizing per GB/T 13912 for outdoor service.
Preparation before Installation
Preparation decides more than half of installation quality. First, verify the sleeper condition: rotten timber, cracked concrete, or damaged inserts must be replaced before any new spike is installed. Second, mark the spike positions so the spikes do not hit rail joints, pre-existing holes, or the sleeper edge. Third, clean the position and remove debris. For timber ties, pre-drill a pilot hole of about 80% of the spike shank diameter; for screw spikes in timber, drill to the full thread length with a hole diameter approximately equal to the thread core diameter. Pilot holes reduce splitting of the timber and make driving force predictable.
Driving and Tightening Procedure
Dog spikes are driven vertically through the rail base or against the rail foot with a sledge hammer or a mechanical spike driver; the head must seat firmly against the rail foot without over-driving, which deforms the rail base. Screw spikes are started by hand for a few turns to confirm the thread engages correctly, then tightened with a torque wrench or an impact driver. As a working value for M24 screw spikes in timber or dowel anchors, the tightening torque is typically 150-200 N.m; the exact value should follow the fastening system design and the sleeper specification. Over-tightening strips the thread in the timber, while under-tightening leaves the spike loose under vibration. Spikes in the same sleeper should be tightened in a balanced sequence so the rail sits evenly on the baseplate.
Inspection and Re-Tightening
Within two hours of installation, inspect every spike for seating, alignment and head contact; a spike that is not fully seated will work loose quickly. After the first train passages, re-check torque or seating, because new spikes settle into the timber or the anchor. Routine maintenance should include a visual patrol for raised heads, rust streaks and loose spikes, plus gauge measurement at the spikes. Spikes that have been pulled or worked loose should be replaced, not re-driven into the same hole, because the damaged thread or wood fiber no longer provides the design pull-out resistance.
Frequently Asked Questions
Q1: What is the difference between a dog spike and a screw spike?
A dog spike is driven into timber and holds by friction and wood fiber compression, while a screw spike is threaded and holds by thread engagement, giving higher pull-out resistance, especially in concrete sleepers with inserts or dowels.
Q2: Should I pre-drill before driving a spike?
Yes, on timber ties a pilot hole of about 80% of the shank diameter prevents splitting and gives consistent seating. Screw spikes always require a pilot hole at the thread core diameter.
Q3: What torque should be used for an M24 screw spike?
A typical tightening torque is 150-200 N.m, but the fastening system design and sleeper type govern the exact value. Use a calibrated torque wrench and re-tighten after the first traffic passages.
Q4: How often should spikes be inspected?
Newly installed spikes should be re-checked after the first trains pass, then included in the normal track patrol. Loose, raised or rusted spikes in high-stress zones such as curves and turnouts need more frequent attention.
Q5: Can a loose spike be re-driven into the same hole?
No. A worked hole has lost its holding capacity; re-driving gives a false impression of security. Replace the spike and, where the timber is damaged, relocate the spike or renew the sleeper.