Test Measurements and Performance Evaluations of In-Service Railway Asphalt Trackbeds

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Test Measurements and Performance Evaluations of In-Service Railway Asphalt Trackbeds

Mensagem por Manuela » 05 Set 2016, 14:20

Autor: Jerry G. Rose, PE.

During the past twenty-five years the use of Hot Mix Asphalt (HMA) as a subballast
layer, or underlayment, within the track structure has steadily increased until it is becoming
standard practice in many areas of the United States. This asphalt-bound impermeable layer,
typically 5 to 8 in. (125 to 200 mm) thick, provides a “hardpan” to protect the underlying
roadbed and to support the overlying ballast and track. Long-term performance studies on
numerous HMA installations attest to the improved attributes and economic benefits of the
asphalt layer, particularly on heavy tonnage lines traversing areas of marginal geotechnical
engineering characteristics.
Recent studies involve instrumenting HMA trackbeds with earth pressure cells and
displacement transducers to measure pressure levels and distributions within the track structure
and rail deflections under moving trains. These tests, conducted in real time domain train
operations, confirm the positive attributes of the asphalt layer. Results are presented in detail for
test installations on a CSX Transportation heavy tonnage mainline and at the Transportation
Technology Center (Pueblo) low track modulus heavy tonnage test track.
KENTRACK, a finite element, layer-elastic trackbed structural design computer
program, is utilized for determining the effects of varying trackbed materials, component
thicknesses, and designs on pressure distributions in the track structure. Predictive values from
the KENTRACK model are compared with in-track measurements. The predictive values,
obtained from KENTRACK, compare well with in-track measurements for similar conditions
providing a measure of credibility for the model.
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