Test of Hot-Mix Asphalt Trackbed over Soft Subgrade under Heavy Axle Loads

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Test of Hot-Mix Asphalt Trackbed over Soft Subgrade under Heavy Axle Loads

Mensagem por Manuela » 05 Set 2016, 16:30

Autores: Dingqing Li, Jerry Rose and Joseph LoPresti.

Work performed by
a subsidiary of the Association of American Railroads
April 2001.

Tests of hot-mix asphalt (HMA) underlayments as a method for strengthening soft
subgrade support show that this technique facilitates the development of adequate
track modulus, reduces subgrade stresses under heavy axle loads, and impoves
track geometry performance. Since its installation, approximately 100 million
gross tons (MGT) have been accumulated over this test track. To date, the track has
been performing well, without requiring any surfacing maintenance. As comparison,
18-inch conventional track construction on this subgrade required surfacing at
an average cycle of 15 million gross tons.
The test track, using HMA underlayments, was built over the soft subgrade in
the Heavy Tonnage Loop (HTL) at the Transportation Technology Center, in the
summer of 1999. The entire test section is about 700 feet long and consists of two
segments: 4-inch HMA and 8-inch HMA underlayments. A 4-inch subballast layer
was used between the soft subgrade and the two HMA underlayments. The total
combined thickness of ballast, HMA and subballast for the entire section was 20
inches at the time of construction.
Preliminary test results indicate that both the 4- and 8-inch HMA underlayments
facilitate the development of adequate track modulus in the range of 2,600
to 3,500 lbs/in/in, compared to approximately 2,000 lbs/in/in for an 18-inch conventional
granular track over this soft subgrade. The subgrade stresses generated
under 39-ton axle load train operations have also been reduced to an acceptable
The HMA underlayments are also being measured to determine their effective-
ness in stabilizing both subgrade moisture content and avoiding oxidation.
Ultimately, it is the intent of this test program to provide sufficient data for the
development and acceptance of specifications for HMA underlayment.
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