Selection of rail pad thickness and line adaptation
- What are the common thicknesses of under-rail pads?
Common thicknesses are 5mm, 10mm, 12mm, and 15mm. Ordinary railways mostly use 10mm thick pads, high-speed railways 12mm-15mm, which can provide better elasticity. Urban rail transit, with small loads, can use 5mm-10mm pads. Thickness selection must match the designed track elasticity, avoiding too thick or thin affecting driving stability.
- How does increasing thickness by 1mm affect track elasticity?
Increasing thickness by 1mm usually improves track elasticity by 3%-5%. For example, a 10mm pad has an elastic coefficient of 50kN/mm, and an 11mm one may drop to 48kN/mm, with better buffering effect. But too thick (over 20mm) will reduce track stiffness and increase rail displacement, which must be controlled within the design range. High-speed railways adjust according to speed, with 350km/h lines mostly using 15mm pads.
- Why do heavy-haul railways choose thinner pads?
Heavy-haul railways have large axle loads, choosing 8mm-10mm thin pads can increase track stiffness and reduce rail settlement. Thick pads are easy to compress and deform under large loads, leading to track irregularity and increased maintenance frequency. Thin pads with high-strength materials (such as polyurethane) can ensure certain elasticity, bear heavy loads, and extend service life.
- What problems can uneven pad thickness cause?
A thickness difference exceeding 1mm will cause track height deviation, vibration when the train passes, and acceleration increase by 10%-15%. Local over-thickness will cause rail inclination, gauge deviation, and poor wheel-rail contact. Long-term unevenness will aggravate ballast compaction and increase maintenance costs. Check thickness during laying to ensure deviation ≤0.5mm in the same section.
- How to determine the thickness when replacing pads?
According to track detection data, select 1mm-2mm thicker pads in areas with large height deviation. The outer side of the curve can be slightly thicker than the inner side (difference 1mm) to balance stress. After replacement, retest track geometric parameters to ensure height deviation ≤1mm and direction deviation ≤1mm/m. The thickness of turnout area pads must match the switch tie to avoid interference.