Improved performance of geosynthetics enhanced ballast: laboratory and numerical studies

Abstract

Ballasted rail tracks form one of the most important worldwide transportation modes in terms of traffic tonnage, serving the needs of bulk freight and passenger movement. High impact and cyclic loads can cause a significant deformation leading to poor track geometry. In order to mitigate these problems, the concept of the inclusion of geosynthetics in rail tracks is introduced. This paper presents the current state-of-the-art knowledge of rail track geomechanics, including results obtained from laboratory testing, field investigations and numerical modelling to study the load-deformation behaviour of ballast improved by geosynthetics. The shear stress-strain and deformation behaviour of geosynthetic-reinforced ballast are investigated in the laboratory using a large-scale direct shear test device, a track process simulation apparatus and a drop-weight impact testing equipment. Computational modelling using the discreteelement method is employed to simulate geosynthetic-reinforced ballasted tracks, capturing the discrete nature of ballast aggregates when subjected to various types of loading and boundary conditions. Discreteelement modelling is also used to conduct micromechanical analysis at the interface between ballast and geogrid, providing further insight into the behaviour of ballast subjected to cyclic loadings. These results provide promising approaches to incorporate into existing track design routines catering for future high-speed trains and heavier heavy hauls.

Pullout Behavior of Different Geosynthetics—Influence of Soil Density and Moisture Content

“…Geosynthetics have been widely used as a reinforcement material in several geotechnical engineering applications, such as roadway and railway layers and embankments Ashmawy and Bourdeau, 1995;Lee and Wu, 2004;Ravi et al, 2014;Ferreira et al, 2016a;Nimbalkar and Indraratna, 2016;Indraratna et al, 2018Indraratna et al, , 2019Ngo et al, 2018;Byun and Tutumluer, 2019;Tatsuoka, 2019). In such applications, the interaction mechanism between the geosynthetic and the surrounding material is of primary importance.…”

Application of geoinclusions for sustainable rail infrastructure under increased axle loads and higher speeds

“…The influence of the geometry and aperture size of geogrids and confining pressure on the interface behaviour of the composite assembly has been examined by Indraratna et al [14] and Ngo et al [43]. Seven types of geogrids, namely G1 to G7 (Table 1) with square, rectangular, and triangular geometry and different aperture sizes were tested using the direct shear box.…”

“…9 Schematic of the shear box used for the experiment zones having different track stiffness (e.g. bridges, tunnels and road crossings) which exacerbates the deterioration of the track elements and implies the need for more frequent maintenance operations [9,13,16,18,43,52]. Furthermore, with the significant increase in axle loads and train speeds, the vibrations attributed to wheel and rail imperfections are further intensified and the safe operation of trains can be compromised, which is why the application of polymeric inclusions, such as geogrids and energy-absorbing rubber sheets in rail tracks, has raised increasing attention in recent years.…”

“…In addition, impact forces generated by wheel and/or rail irregularities or imperfections or at transitions zones (e.g. bridge approaches and exits, road crossings) may exacerbate track deterioration initiating frequent maintenance cycles [9,43,52]. As a result, ballast assembly becomes degraded/ fouled and its grain angularity, overall strength and ability to drain off water are seriously compromised [27,63,64,66].…”

Use of Geogrids and Recycled Rubber in Railroad Infrastructure for Enhanced Performance

“…In addition to the repeated loads exerted by moving wheels, rail structures are commonly subject to dynamic impact forces of high magnitude produced by rail irregularities (e.g., corrugations, imperfect welds, rail dips) as well as imperfections such as wheel flats. These impact forces can likewise be generated at transition zones involving abrupt variations of vertical track stiffness, such as at the approaches to tunnels, bridge or viaduct and level crossings, or where there is a sudden change from conventional ballast to slab track intensifying ballast breakage and adversely affecting track stability [11][12][13][14][15]. One potential method of enhancing the substructure capacity to withstand the large cyclic and impact loads induced by fast-moving heavy-haul trains is to improve the performance of the ballast layer using plastic (e.g., geogrids) and rubber inclusions (e.g., rubber mat, tire cell, and rubber crumbs) [2,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30].…”