In-track measurement of ballast-tie interface pressures under heavy-axle-loads

摘要

The ballast-tie interface is an important area of the conventional railroad track structure. Contributing to functions of the tie and ballast, the interface serves the purpose of distributing pressure through the ballast layer, allowing for adjustment of track geometry (tamping/surfacing) and providing vertical, lateral and longitudinal track stability. The ballast-tie contact surface is typically approximated as two-thirds the tie footprint (the outer third on each end of the tie). In North American practice, a uniform and average pressure distribution is assumed over this contact surface. In reality, however, ballast-tie pressures vary continuously along the length of the tie. The variability of pressure along the length of the tie has a significant impact on the design tie bending strength that is required. Concrete tie center cracking is one possible failure when loading conditions exceed the tie's design capacity. More specifically, the ballast-tie interface is characterized by high pressures caused by the individual angular ballast particles supporting the tie. Low contact area and the resulting high pressures on the ballast particles and tie may contribute to ballast particle breakage, tie surface degradation, ballast degradation and track settlement.