Every year, railroads dedicate a great deal of capital and maintenance expense towards the creation and upkeep of high quality ballast layers. Enduring well-designed ballast is quite literally the foundation on which a successful rail line operates. With ballooning rail traffic carrying heavier loads than ever, GEOWEB cellular confinement (Geocell) effectively takes the pressure off critical ballast systems.
Oregon State University (OSU) recently performed state-of-the-art, three-dimensional dynamic Finite Element modeling to analyze the reinforcing benefit of GEOWEB geocells in railway applications. This study was completed in cooperation with the University of Kansas (KU) who simultaneously performed a testing program of Geocell reinforced ballast placed over weak subgrade material using HDPE GEOWEB material.
The digital modeling results were reinforced by the laboratory tests and showed a significant decrease in settlement of the railway ballast when GEOWEB confinement was used. The use of GEOWEB technology not only decreased settlement, but reduced pressure on point-to-point aggregate load transfer contact which in turn resulted in less damage to ballast aggregate particles leading to less progressive deformation and longer maintenance frequencies of the entire ballast embankment. In short, more cycles means less track down-time for maintenance.
The research results were clear. The benefits of applying GEOWEB Geocell confinement for reinforcement of real ballast over weak subgrades includes:
- Significant decrease in settlement of the railway ballast. GEOWEB confinement influence reduced settlement by to up 50% under heavy freight loadings over weak sub grades.
- Decrease in subgrade interface pressure by nearly 50% for weak subgrades. The decreased pressure in subgrade results in lower subgrade settlements.
- Increase in ballast resiliency after many cycles—resulting in decreased rate of cyclic settlement.
- Decrease in lateral heave and movement of the ballast material.
- Redistribution of vertical stresses on the subgrade—resulting in higher shear strength and reduction in plastic deformation.
- For the largest loading conditions used in the analysis, the strains in the GEOWEB geocell were low (less than 1%) and within the elastic range for typical geosynthetic materials. The maximum tensile strains were localized at the bottom corners of the GEOWEB cells, illustrating the importance of adequately durable seams.
- Strains in the GEOWEB ballast layer were low (less than 1%) even under heavy, freight loadings over very soft sub grades. Stress concentrations were found at the seams, highlighting the importance of GEOWEB seam strength during loading condition.
A Better Built Ballast
The benefits of GEOWEB confined ballast are substantiated through rigorous testing. Conventional ballast reinforcing materials (eg geogrids, Hot Mix Asphalt (HMA)) do not have the strengthening attributes that GEOWEB geocells can provide, especially in soft subgrades. Building a more stable ballast layer with less settlement, higher shear strength, and less maintenance requirements is possible when built with GEOWEB geocells.