Stress-Strain Degradation Response of Railway Ballast Stabilized with Geosynthetics

Abstract

Large cyclic loading on ballasted railroad tracks is now inevitable owing to an increased demand for freight and public transport. This leads to a progressive deterioration and densification of railroad ballast and consequently to the loss of track geometry and differential settlement. Understanding these complex stressstrain and degradation mechanisms is essential to predict the desirable track maintenance cycle, as well as the design of new track. This paper presents the results of cyclic drained tests and numerical studies carried out on a segment of model railway track supported on geosynthetically reinforced railroad ballast bed. The relative performance and effectiveness of single-and dual-layer configurations of geosynthetic reinforcement was evaluated using a large-scale prismoidal triaxial chamber. Laboratory tests on unreinforced and reinforced railway track were simulated in a numerical model, and the results were then analyzed to better understand the distribution of displacements and stresses inside the railroad ballast layer. It was observed that in view of strain and breakage control, both the type of reinforcement and its layout played a vital role in improving the capacity of the track. These laboratory test findings were supported by the predictions from an advanced elastoplastic numerical analysis. Abstract: Large cyclic loading on ballasted railroad tracks is now inevitable owing to an increased demand for freight and public transport. This leads to a progressive deterioration and densification of railroad ballast and consequently to the loss of track geometry and differential settlement. Understanding these complex stress-strain and degradation mechanisms is essential to predict the desirable track maintenance cycle, as well as the design of new track. This paper presents the results of cyclic drained tests and numerical studies carried out on a segment of model railway track supported on geosynthetically reinforced railroad ballast bed. The relative performance and effectiveness of single-and dual-layer configurations of geosynthetic reinforcement was evaluated using a large-scale prismoidal triaxial chamber. Laboratory tests on unreinforced and reinforced railway track were simulated in a numerical model, and the results were then analyzed to better understand the distribution of displacements and stresses inside the railroad ballast layer. It was observed that in view of strain and breakage control, both the type of reinforcement and its layout played a vital role in improving the capacity of the track. These laboratory test findings were supported by the predictions from an advanced elastoplastic numerical analysis.

Performance improvement of rail track substructure using artificial inclusions – Experimental and numerical studies

“…Table 2. Macromechanical parameters adopted for ballast in FEM (data sourced from Nimbalkar et al [7], Indraratna and Nimbalkar [45]). Table 1.…”

“…Although the actual stress-strain states may not be simulated exactly, especially near the boundaries, this numerical track model reasonably simulates realistic track behavior [45].…”

“…The deformation of ballast is characterised by three phases [45]; the first phase is immediate deformation under the first loading cycle, the second phase is an unstable zone where rapid deformation attributed to the reorientation and rearrangement of particles occurs along with significant breakage, and the third phase is often called 'stable shakedown' where the rate of increase of deformation is insignificant. Thus, ballast deformation during cyclic loading can be determined as [45]:…”

“…The Hardening Soil (HS) model was based on an appropriate isotropic hardening plasticity to simulate the strain-hardening behaviour of ballast. More details of this approach are given in Indraratna and Nimbalkar [45]. The sub-ballast and subgrade were both represented with a standard Mohr-Coulomb 3 ) was also modelled as a linear elastic material [7], and linear elastic tension elements were used to model the geosynthetic layer.…”

“…Equation (19) is differentiated with respect to the loading cycle (N) and incremental axial strain is given as [45]: testing conditions, the incremental volumetric strain under cyclic loading is expressed as [45]:…”