CHARACTERIZATION OF RAILROAD BALLAST BEHAVIOR UNDER REPEATED LOADING USING A NEW LARGE TRIAXIAL TEST SETUP

摘要

Characterizing railroad ballast behavior under repeated train loading is of significant importance forevaluating field settlement or permanent deformation potentials of unbound aggregate ballast layers. Toproperly characterize ballast behavior under dynamic loading, a new triaxial test setup was recentlydeveloped at the University of Illinois at Urbana-Champaign. Capable of accommodating cylindricalspecimens with a diameter of 305 mm (12 in.) and a height of 610 mm (24 in.), this closed-loop servohydraulic test setup utilizes a load cell and four displacement transducers mounted on the specimen toquantify deformation behavior under loading. Unique features of the test setup are first presented in thispaper followed by the procedures adopted for sample preparation and compaction. Preliminary test resultsevaluating effects of different applied stress states as well as geogrid reinforcement on ballast behaviorestablished the consistency and repeatability of this new test equipment. Next, laboratory findings arepresented from an ongoing research study aimed at investigating the effects of different ballast types andfield degradation trends on permanent deformation accumulation. The ballast type with the highest MillAbrasion Value was found to accumulate the highest permanent deformation under repeated load triaxialtesting. Permanent deformation trends observed for four other ballast types showed direct correlations tothe degrees of particle degradation observed in track sections constructed using these ballast materials andtrafficked for approximately 18 months with a total track usage of 320 million gross tons.