Rail Pad Thickness Selection and Track Elasticity Adjustment
- What are the common thickness specifications of under-rail pads?
Under-rail pads with thicknesses of 6mm, 8mm and 10mm are commonly used in ordinary lines, which can meet the elastic requirements under general loads; high-speed railways mostly use under-rail pads with thicknesses of 12mm and 15mm to reduce vibration and impact, and even 20mm thick pads are used in some special sections; heavy-haul railways, due to large loads, need to take into account both elasticity and bearing capacity, and commonly use pads with thicknesses of 10mm and 12mm; urban rail transit mostly uses elastic pads with thicknesses of 8mm, 10mm and 12mm to reduce noise.
- How does the pad thickness affect track elasticity?
Within a certain range, the greater the pad thickness, the better the track elasticity. For example, a 10mm thick pad has an elastic coefficient 20% - 30% lower than a 6mm thick pad, which can better absorb the vibration generated by train loads. However, when the thickness exceeds 20mm, the elastic growth tends to be gentle, and the pad is prone to excessive deformation, affecting track stability. In addition, pads of different materials have different elasticity under the same thickness, and rubber pads are 15% - 20% more elastic than polyurethane pads.
- What are the requirements for the thickness of under-rail pads for different line types?
High-speed railways require uniform and moderate track elasticity, and the pad thickness is generally 12 - 15mm, so that the vertical stiffness of the track is controlled at 40 - 60kN/mm to ensure the stability of high-speed train operation. Heavy-haul railways need high track stiffness, and the pad thickness is mostly 10 - 12mm to avoid excessive deformation leading to gauge changes. Urban rail transit focuses on shock absorption and noise reduction, and the pad thickness is usually 10 - 12mm, and high elastic materials are selected to reduce the noise transmitted from vibration to the surrounding environment.
- How to adjust the pad thickness according to the measured track elasticity?
Measure the vertical stiffness of the track with a track elasticity tester. If the measured stiffness is greater than the design value (for example, the design stiffness of high-speed railway is 40 - 60kN/mm, and the measured stiffness is 70kN/mm), it indicates that the elasticity is insufficient, and a thicker pad needs to be replaced (such as replacing 12mm with 15mm); if the measured stiffness is less than the design value and the elasticity is too large, a thinner pad should be replaced (such as replacing 15mm with 12mm). After adjustment, re-measure until the elasticity meets the design requirements.
- What effects will improper selection of pad thickness have on the track?
When the thickness is too small, the track elasticity is insufficient, and the impact generated by the train load is directly transmitted to the sleepers and ballast, which accelerates the ballast compaction speed and shortens the service life of the sleepers by 30% - 40%. When the thickness is too large, the track deforms too much under load, the rail is prone to lateral displacement, and the gauge deviation exceeds the standard, which affects the safety of train operation. At the same time, the pad is prone to aging under long-term large deformation, reducing its service life.