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The project was
located on a dead-end road in Richmond, Maine. The road has fairly light
traffic, but once a month between 10 and 40 loaded dump trucks deliver sewage sludge to two
farms on the road. The gravel surfaced road becomes severely rutted during
spring thaw. Tire shreds were used to try to insulate the road and reduce
the depth of frost penetration during the winter, effectively eliminating the
thawing that causes the heaving of the road surface in the spring.
Figure 1 shows
plan and longitudinal views of the roadway, and how it has been divided into sections. There
are five sections that include tire chips. Table 1 gives the thickness of
each layer of material placed beneath the roadway. Geotextiles were used for only section A
of the roadway. The entire road was
surfaced with 4 inches of gravel. Figure 2 gives a typical cross section
of the roadway.
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Figure 1. Plan and longitudinal views of test sections of Richmond field
trial
Table 1. Summary of test section configuration of Richmond field trial
Figure 2. Typical cross section of Richmond field trial
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The tire shreds
used in this project had a maximum size of about 2 inches, and were made from
approximately 20,000 steel and glass belted tires. The tire shreds were
uniformly graded, and the sand and gravel mixture used as fill over the tire
shreds was well-graded.
Thermocouples and
resistivity gauges were used to measure the depth of frost penetration beneath
the roadway. Figures 3 and 4 show the location of these instruments.
Groundwater wells were also installed to keep track of the level of the ground
water table and to take samples for water quality testing.
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Figure 3. Location of thermocouples and resistivity gauges
Figure 4. Longitudinal section showing thermocouples and resistivity
gauges in Section C
Figure 5
shows the maximum depth of frost penetration for each section of the
roadway. For control sections, the frost penetration ranged from 46
to 63 inches. For tire shred sections A, B, D, and E, frost
penetration ranged from 36 to 40 inches. Tire shreds work better as
insulators when the material is placed closer to the surface of the
roadway. For this reason, frost penetration was deeper for section C
than for A and B.
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Figure 6 shows the
change in the depth of frost penetration over time. The control section
had an increase in frost depth throughout the entire winter. Sections A,
B, and C had reduced rates of frost penetration compared to the control section,
and sections D and E, had no increasing frost depth after early January.
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Figure 6. Depth of frost penetration versus date - winter of 1993-4
(Humphrey and Eaton, 1995)
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A comparison of
temperatures above and below the tire shred layers can be seen in the
temperature profiles in figure 7.
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Figure 8 gives
frost heave measurements for the different sections of the road. Tire
shreds reduced heave by up to 25%.
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