Non-linear soil behaviour on high speed rail lines

Abstract

This paper gives new insights into non-linear subgrade behaviour on high speed railway track dynamics. First, a novel semi-analytical model is developed which allows for soil stiffness and damping to dynamically change as a function of strain. The model uses analytical expressions for the railroad track, coupled to a thin-layer element formulation for the ground. Material non-linearity is accounted for using which iteratively updates the soil material properties. It is validated using published datasets and in-situ field data. Four case studies are used to investigate non-linear behaviour, each with contrasting subgrade characteristics. Considering an 18 tonne axle load, the critical velocity is significantly lower than the linear case, and rail deflections are up to 30% higher. Furthermore, at speeds close-to, but below the non-linear critical velocity, dynamic amplification is highly sensitive to small increases in train speed. These findings are dependent upon soil material properties, and are important for railway trackearthwork designers because often 70% of the linear critical velocity is used as a design limit. This work shows that designs close to this limit may be still at risk of high dynamic effects, particularly if line speed is increased in the future.

Railway critical speed assessment: A simple experimental-analytical approach

“…The most suitable geotechnical test that should be performed is dependent on the intended engineering analysis. Although trains running at critical speed can cause strain-induced non-linear behavior (as shown by Alves Costa et al [10] and more recently by Dong et al [28]), the computation of the critical speed must always be based on the low strain properties of the ground profile. Therefore, geophysical testing is the most suitable technique to obtain the required properties, namely the low-strain wave propagation velocities in the ground.…”

High speed railway ground dynamics: a multi-model analysis

“…This energy causes elevated strain levels, which may lie in the 'large-strain' range, resulting in non-linear soil-stiffness degradation during train passage. This reduced soil stiffness causes increased track deflections [48].…”

Geodynamics of very high speed transport systems

“…it has no limitations regarding low-stiffness sandwich layers, or layer thicknesses). It assumes that the soil behaviour is linear elastic, and non-linear ( [33], [34], [35]) behaviour is ignored.…”