Methods of improving tracks and using mud pumping sheets have been recommended as a measure to avoid mud pumping for ballast tracks. However, in recent years it has become very difficult to apply such methods due to the high costs involved and the difficulty of execution. As a low-cost measure to avoid mud pumping, therefore, the preferred method now involves improving track strength through the application of chemicals. If the chemicals bind the ballast too strongly, however, it will obstruct normal track maintenance work. In addition, some chemicals cause environmental contamination or problems related to waste treatment. With these drawbacks in mind, the RTRI developed methods to:
(1) Re-align tracks using air pressure to inject granular filler under sleepers
(2) Maintain the strength of existing ballast when saturated with water using a biodegradation polymer
For method (1), the RTRI implemented a test to inject granular filler under sleepers without loosening the fine-grain soil-containing ballast to demonstrate that tracks can easily be re-aligned (Fig. 1).
Method (2) maintains the strength of the saturated ballast by increasing cohesion of the fine-grained soil in the ballast (Fig. 2). In a life-size model test, only minor ballast settlement was observed (Fig. 3), and normal track maintenance work remains possible after the application of the technique. This low-cost method features a minimal environmental burden as the replaced ballast can be treated as normal surplus soil.
The RTRI plans further studies towards the commercial application of this method.
|