Technology Digests / FAST® Baseline Ballast and Subgrade Characterization

TD24-018

May 9, 2025
Authors
  • Stephen Wilk
  • Dingqing Li
  • Yin Gao
  • Christopher Johnson
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Key Findings

  • The new FAST® track has a uniform, strong, well-draining sandy subgrade. This subgrade is desirable for both rail and tie testing and is similar to the test bed used prior to MxV Rail's relocation in 2022. Any poor subgrade testing would require a dedicated test section.
  • The majority (70-80 percent) of the settlement of the new FAST loop occurred in the initial 40 MGT. Currently, at 100 MGT, the track continues to settle at a lower rate. FAST has required minimal maintenance from a substructure standpoint, with the bridge approaches being the main exception.
  • Concrete ties with UTPs showed:
    - Approximately 25 percent higher lateral tie resistance in compacted track compared to concrete ties with no pads.
    - Settlement and track modulus that are comparable to wood ties.

FAST® Baseline Ballast and Subgrade Characterization

MxV Rail took multiple baseline ballast and subgrade measurements at the newly constructed Facility for Accelerated Service Testing (FAST®) track near Pueblo, CO between March 2023 and June 2024. The objectives for gathering these measurements were wide ranging, including: 1) providing validation of subgrade conditions that are desirable for track component testing; 2) providing insight into the track settlement behavior of newly constructed track and subgrade; and 3) providing a baseline for comparison for any future testing or change in track substructure conditions. FACILITY FOR ACCELERATED SERVICE TESTING (FAST®) FAST operates on a 2.8-mile-loop track that provides a test bed for railroad component testing (infrastructure and vehicle and performance evaluation under a severe but controlled loading environment. Historically, FAST has operated on a competent substructure (ballast, subgrade, drainage), which is desirable for rail and tie testing because it allows for consistency, whereas a poor substructure may compromise rail and tie…