25 years of heavy axle load railway subgrade research at the Facility for Accelerated Service Testing (FAST)

This paper presents a summary of more than two decades of heavy axle load (HAL) railway subgrade research conducted at the Facility for Accelerated Service Testing (FAST). Railway subgrade, if inadequate and not reinforced/improved, can deform and fail progressively, causing significant track geometry degradation under HAL train operations. To understand how railway subgrade behaves under HAL and develop guidelines for design, maintenance and remediation, a number of tests were conducted in multiple phases at FAST to determine how a “soft” subgrade test section would affect track performance and to evaluate remediation methods that can be used to improve soft subgrade support for HAL train operations. Since its inception in the early 1990s, this subgrade testing program has produced a body of knowledge about railway subgrade behavior under 35.4-tonne axle loads. In addition to generating track degradation and maintenance demand data, the testing program provided valuable insight into the relationship between subgrade behavior and track performance. Results were obtained to understand how wheel loads were transferred to the subgrade, subgrade failure mechanisms, and how various soft subgrade remediation techniques performed.