May/June 2023 - 20

Sound Transit
In all, it took the better part of
a year to identify the factors that
contributed to the problem and
to validate the root cause, Rajaram
said.
" But once we changed the
grinding program, the problem
went away, " he added.
The experience led Sound TranA
Link train pulls
into Tukwila
International
Boulevard
Station during
an evening
commute.
Photo: Glenn Landberg
/ Sound Transit
Sound Transit's database of
noise readings showed unusually
high noise levels (in the high
800-Hz frequency range) in the
clip-failure areas. Further investigation
found the 820-HZ track
noise corresponded to the natural
frequency of the e-clips used in
the segment. To determine the
root cause of the high-frequency
resonance in this segment,
Sound Transit looked at track
geometry, construction tolerances,
fastener design and wheel
and truck performance of the vehicles
operating on the line. It also
investigated research indicating
the deep grinding marks left in
the rail were associated with the
speed of the grinding motors. The
marks appeared at approximately
one-inch intervals wherever a clip
had failed.
A deeper dive into the noise
data map showed noise spikes
lined up with locations of the
broken clips. The data provided
fingerprints of frequencies at hot
spots where the natural frequency
of the track system matched the
20 Mass Transit | MAY/JUNE 2023
frequency of the wheel/rail-generated
noise pattern from the rail
grinding marks, Rajaram said.
Sound Transit brought in Advanced
Rail Management (ARM),
which is now part of the Global
Rail Group, to assess rail surface
conditions in the clip-breakage
area and to develop, along with
Loram Maintenance of Way, the
grinding contractor, a method of
" polishing " the rail with softer-grit
grinding stones to leave a smoother
surface finish. ARM and the National
Research Council of Canada
(NRC) were charged with assessing
wheel conditions and coming
up with a profile design and truing
method to reduce wheel surface
roughness. Their study concluded
that while powered wheels tended
to hollow wear, the IRWs, which
wore more heavily in the flange,
tended to wear more asymmetrically
- information that has
since guided Sound Transit's
wheel truing strategy and led to
better uniformity and a smoother,
quieter wheel running surface,
Rajaram said.
sit to develop a specification to
procure the wheel/rail expertise
that could identify and assess
the potential relationships between
noise, wheel and rail wear,
defect growth and the ability to
address them. In addition to the
more typical requirements for
rail grinding to remove surface
defects re-shape the rail profile,
the Sound Transit spec incorporated
a polishing step to ensure
the wavelength signature of the
finished rail will mitigate the types
of noise and vibration-related
problems previously encountered
on the system. Its surface finish
requirement is significantly more
stringent than the North American
grinding standard and beyond
what any grinder on the continent
had achieved.
" We found that what works
on other properties doesn't seem
to work here, " Bailey said. " The
polishing step is really important
to us. "
Sound Transit subsequently
awarded ARM/GRG a longterm
contract to provide wheel/
rail-related engineering support,
oversee its rail grinding program
and provide quality assurance that
the requirements for re-profiling,
removing defects from the surface
of the rail and that the all-important
" polishing, " or surface-finish
requirements were met.
To get it done, ARM conducted
an overall assessment of the system,
including track geometry and rail
corrugation measurement using a
Corrugation Analysis Trolley, ultrasonic
and pre- and post-grinding
Draisine eddy current testing to
measure rail surface crack length,
depth, geometry and proximity to
other cracks.
May/June 2023

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