Behavior of Geogrid Reinforced Ballast at Different Levels of Degradation

Abstract

Geogrids have been successfully used in highway applications for stabilization and reinforcement purposes. Recent research efforts have also been dedicated to study geogrids in railway applications, especially for ballast reinforcement. Ballast typically containing large sized aggregate particles with uniform gradation is an essential layer in railway substructure to facilitate load distribution and drainage. However, the reinforcement effect of geogrids in ballast has not been thoroughly investigated yet. Especially with accumulation of tonnage, ballast will get fouled increasingly due to aggregate degradation or contamination by other materials, affecting aggregate-geogrid interlock mechanism at different levels of degradation. In this study, monotonic triaxial strength tests performed on both clean and fouled ballast specimens have been reinforced by geogrids and tested using a large scale triaxial test device recently developed at the University of Illinois specifically for ballast size aggregate materials. Two different geogrids with square and triangular shaped apertures are used in comparison. To further investigate the geogrid reinforcement mechanisms, an imaging based Discrete Element Modeling (DEM) approach was also adopted with the capability to create actual ballast aggregate particles as three-dimensional polyhedron blocks having the same particle size distributions and imaging quantified average shapes and angularities. By addressing adequately the particulate nature of different sized and shaped ballast aggregate particles and their interactions with each other at contact points, and through the innovative use of membrane elements surrounding the cylindrical ballast specimen, the ballast DEM model accurately captured the strength behavior of both clean and degraded ballast specimens reinforced by geogrids with different aperture shapes.

Three-Dimensional Discrete-Element Modeling of Geocell-Reinforced Ballast Considering Breakage

“…To stabilize railway ballast, studies have been conducted to reinforce ballast using geosynthetics (Chen et al, 2012, Qian et al, 2015, Wang et al, 2016. Chen et al (2012) used DEM to simulate the response of geogrid-reinforced ballast under confined and unconfined conditions.…”

“…Chen et al (2012) used DEM to simulate the response of geogrid-reinforced ballast under confined and unconfined conditions. Similarly, Qian et al (2015) used DEM to examine geogrid-reinforced ballast subjected to triaxial tests, whereas Liu et al (2018) modeled a scaled-down geocell-reinforced railway track structure using DEM.…”

Railroad Ballast Particle Breakage with Unique Laboratory Test Method

“…The authors would like to combine this splitting test with a full-field 3D shape measurement (ATOS fringe projection system) and/or X-ray measurement technique. The measurement method need to be work out [18,34,35,36,37,38,39,40,41,42].…”

Effect of Particle Size Distribution and Packing Characteristics on Railroad Ballast Shear Strength: A Numerical Study Using the Discrete Element Method

“…The mechanism of interlock in geogrids is shown in Figure 2.16. Different factors affecting the interlocking between geogrids and aggregate particles are aggregate size and shape properties, geogrid types and properties, compaction efforts during installation, and loading conditions (Qian et al, 2014). …”

“…The triaxial shear strength test is traditionally performed in the laboratory to evaluate the effects of monotonic and repeated loading on ballast behavior (Indraratna et al, , 2009Suiker et al, 2005;Aursudkij et al, 2009;Lu and McDowell, 2010;Qian et al, 2013Qian et al, , 2014Qian et al, , 2015Mishra et al, 2014a;McDowell and Li, 2016;Ngo et al, 2016).…”