Life Cycle Benefits of Subgrade Reinforcement Using Geocell on a High-Speed Railway – A Case Study
(Room Sagamore 1)
19 Sep 17
9:00 AM
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9:30 AM
Tracks:
AREMA Technical Sessions- Track
Track built on poor or weak subgrade, particularly subgrade with inadequate bearing capacity or “strength” will, in general, experience a greater rate of degradation than track built on good or adequate subgrades. This, in turn, results in shorter intervals between surfacing/tamping events, a costly endeavor for high speed railways with tight track geometry tolerances and limited access to the track. The support structure beneath railway tracks is a complex system working together to distribute the load of passing trains. It is therefore paramount that this structure maintain adequate track support properties both to maintain the track geometry and to maintain the safety of the trains traveling over the rails. During normal operations, track geometry, tends to degrade over time. This is usually manifested through ongoing track geometry measurement, and monitoring of a statistically based Track Quality Index (TQI). This degradation is a byproduct of the cyclical loading applied to the track structure by passing trains causing the slow compacting and settling of the ballast and subgrade. In the case where the subgrade cannot support and distribute the pressure caused from the passing train successfully, accelerated track geometry degradation can take place. This accelerated degradation can be further increased when there exists a variation between support strengths which can lead to increased dynamic loading. A recent research effort sponsored by the Federal Railway Administration allowed for the determination of track geometry performance as a function of subgrade support. . A historically poor performing location in track, on a North American high speed rail line, was identified that was experiencing accelerated track geometry degradation due to poor subgrade. In this research study, a section of this track was reinforced using a Geocell subgrade strengthening material, while adjacent sections on the same subgrade where rebuilt to traditional track standards but without the geocell reinforcement. This entire track segment, both with and without the Geocell material, was also rehabilitated to provide enhanced drainage. During the track renewal, pressure transducers were placed within the subgrade layer under both rails, both in the Geocell and the conventional track zones. The track segment was monitored over a period of one year with both pressure measurements and track geometry data recorded at regular intervals. Analysis of the pressure data showed a significant reduction in pressure at the ballast/subgrade interface, of the order of 50%, with the implementation of the subgrade strengthening Geocell material. Analysis of the track geometry degradation showed a corresponding reduction in the rate of degradation of the order of a factor of 5+, which in turn translates into a significant extension in the surfacing cycle. Overall, the test showed significant benefits associated with the installation of the geocell material in the poor subgrade zone, above and beyond that seen by more traditional rebuild and drainage improvement.