Abstract Manager

For centuries railways have been an integral mode of reliable transport for freight and people.   The design of railway embankments plays an essential role in ensuring their stability and performance, especially their resiliency and safety.

Geosynthetics are widely used in rail embankments optimizing embankment thickness and maintaining necessary layer separation. Cellular confinement systems (CCS), commonly known as geocells, with their three-dimensional geometry, provide additional confinement effects to increase the modulus of stabilized layers, improve the bearing capacity and reduce the lateral spread of stabilized layers. By confining and stabilizing the ballast, CCS improves load distribution and prevents lateral movement, reducing track settlement and lateral deformation over time. CCS also helps to reduce the embankment thickness, lowering material costs while improving track performance under heavy loads and high-speed trains.

Another aspect that has come to recent attention amongst engineers is the vibration attenuation benefit provided by the inclusion of CCS. In railway operation, one of the challenges that need attention during track maintenance is the fouling of ballast and contamination of sub-ballast. Fouling happens with the abrasion of particles and through the migration of fines. While a separation geotextile layer can almost eliminate the vertical migration of fines, the lateral migration amplifies with lateral spreading and vibration from a passing locomotive load. Vibration plays an essential role in the development and migration of fines. CCS vibration attenuation has been shown to reduce the time-dependent change in particle distribution within the embankment.

The performance of any reinforcement is dependent on its material properties. Soil reinforcements are typically plastic materials with a viscoelastic character.  Viscoelastic materials accumulate strain even when the load is within the elastic limit. With an increasing state of strain, the modulus of the material reduces leading to a faster accumulation of higher strain. This effectively reduces the stabilization effect leading to increased maintenance cost. For a design engineer, it is important to understand and co-relate the material index properties to the performance life of an embankment. The current paper studies each of the mechanisms of CCS and links it to fundamental material properties. The dynamic modulus and rate of cumulative strain accumulation are found to play an essential role in overall design performance. The concept was implemented while designing a short span of track for Big Sky rail at Eston Saskatchewan, Canada in 2019. The four-year visual observation and following maintenance cycles validated the design considerations.