Unsaturated Characteristics of Fouled Ballast to Support In Situ Identification of Fouling: Fid-Bau Portal

Unsaturated Characteristics of Fouled Ballast to Support In Situ Identification of Fouling

Sherwood, Robert R. / Kulesza, Stacey E. / Bernhardt-Barry, Michelle L.

Railroad ballasts are poorly graded aggregates that transfer the dynamic weight of railcars from the ties to the subgrade. The ballast section allows for rapid drainage of water through and around the track structure. Fouling is the filling of ballast voids with particles finer than 9.52 mm. Fouling is caused by natural breakdown of ballast during normal track operations, as well as pumping of subgrade from below and capture of falling/flowing materials from above. There is a need for improving the fundamental understanding of ballast degradation characteristics so fouled ballast can be identified in the field more rapidly and reliably. Ballast fouling compromises railway integrity by impeding drainage, and altering the ballast strength. These losses can lead to ballast failure and, ultimately, train derailment. Current state of practice methods for identifying fouled ballast are time intensive, destructive testing methods (e.g., excavation and sieve analysis). Recent advances have been made in nondestructive techniques for ballast fouling detection; however, many of these methods remain unreliable. Fouled ballast is an unsaturated geomaterial; therefore, the objective of this paper is to provide valuable insight into the key relationships between suction and fouling material. Soil water characteristic curves (SWCCs) were measured for five samples of ballast fouling materials using the transient water release and imbibition method. The results indicate that SWCCs from breakdown of ballast were similar to sandy soils and likely did not differ greatly from clean ballast. SWCCs from infiltration of fine grained soil increased the air entry as the percent of fines increased. The SWCC of ballast fouled with coal dust had high air entry and hydraulic conductivity, with lower percent of fines, which was unexpected. These samples present the worst-case scenario of ballast water retention. The long-term goal of this research is to establish the suction and strength characteristics of fouled ballast (including the ballast aggregate) in correlation to ballast fouling and moisture content to improve the assessment of ballast with non-destructive methods, such as ground penetrating radar.