Download Construction of a test embankment using a sand–tire shred mixture

Waste Management 26 (2006) 1033–1044
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Construction of a test embankment using a sand–tire shred
mixture as fill material
Sungmin Yoon a, Monica Prezzi
b
a,*
, Nayyar Zia Siddiki b, Bumjoo Kim
c
a
School of Civil Engineering, 550 Stadium Mall Drive, Purdue University, West Lafayette, IN 47907-1284, USA
Division of Materials and Tests, Indiana Department of Transportation, 120 S. Shortridge Rd. in Indianapolis, IN 46219-0389, USA
c
Dam Safety Research Center, Korean Institute of Water and Environment, Daejon 306-711, Korea
Accepted 10 October 2005
Available online 15 December 2005
Abstract
Use of tire shreds in construction projects, such as highway embankments, is becoming an accepted way of beneficially recycling scrap
tires. However, in the last decade there was a decline in the use of pure tire shreds as fill materials in embankment construction, as they
are susceptible to fire hazards due to the development of exothermic reactions. Tire shred–sand mixtures, on the other hand, were found
to be effective in inhibiting exothermic reactions. When compared with pure tire shreds, tire shred–sand mixtures are less compressible
and have higher shear strength. However, the literature contains limited information on the use of tire shred–soil mixtures as a fill material. The objectives of this paper are to discuss and evaluate the feasibility of using tire shred–sand mixtures as a fill material in embankment construction. A test embankment constructed using a 50/50 mixture, by volume, of tire shreds and sand was instrumented and
monitored to: (a) determine total and differential settlements; (b) evaluate the environmental impact of the embankment construction
on the groundwater quality due to leaching of fill material; and (c) study the temperature variation inside the embankment. The findings
in this research indicate that mixtures of tire shreds and sand are viable materials for embankment construction.
2005 Elsevier Ltd. All rights reserved.
1. Introduction
According to Dickson et al. (2001), there are more than
500 million tires (5.5 million metric tons) stockpiled across
the United States, and 270 million (3 million metric tons)
more are generated each year. About 30% of these tires are
disposed of in landfills, and thousands of tires are left in
empty yards and even dumped illegally. In the state of Indiana, approximately 5 million waste tires (56,000 metric tons)
are generated each year, and there are 40 stockpiles containing millions of tires in different counties (Kaya, 1992). Similar disposal problems also exist worldwide. For example, in
England and Wales, there are about 38 stockpiles with nearly
14 million tires (0.16 million metric tons) stored in them
*
Corresponding author. Tel.: +1 765 494 5030; fax: +1 765 496 1364.
E-mail address: [email protected] (M. Prezzi).
0956-053X/$ - see front matter 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.wasman.2005.10.009
(Hird et al., 2002). Therefore, it is essential to find beneficial
ways of recycling and/or reusing tires.
In civil engineering applications, tires are often used
after they have been shredded to small pieces. Tire shreds
have various shapes and sizes, typically varying between
50 and 300 mm (ASTM D 6270-98). The steel belting is
sometimes removed during processing of the tire shreds.
The market for scrap tires in civil engineering applications
has increased steadily in the last decade. Approximately 12
million scrap tires (0.13 million metric tons) were used in
civil engineering applications in 1995, and 15 million
(0.17 million metric tons), in 1996. These applications
include leachate collection systems, landfill cover, artificial
reefs, clean fill for road embankments, roadbed support,
and similar projects (Liu et al., 2000).
There are several advantages of using tire shreds in civil
engineering applications. One of the most important characteristics of tire shreds is that they are a lightweight material. When roads are constructed across weak and
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S. Yoon et al. / Waste Management 26 (2006) 1033–1044
compressible soils, stability and settlement considerations
are critical. Various lightweight materials have been used
in the construction of fills in order to reduce the weight
of highway structures over these soils. Table 1 shows the
unit weight and approximate cost of tires shreds, with the
corresponding values of other widely used lightweight
materials (Elias et al., 1998; Holtz, 1989; ASTM D 627098). One advantage of using tire shreds either as a lightweight fill material in embankments or as retaining wall
backfills is that tire shreds are not biodegradable and thus
are more durable. The cost of tire shreds varies from $5 to
$50 per m3 (1 m3 is approximately 0.45 ton), depending on
the quality of the tire shreds (personal communication with
tire shredding companies in the State of Indiana: C.C.E.
Inc., Elk Distributing Inc., and Tire Recyclers of America,
LLC., 2002). Tire shreds are relatively inexpensive when
compared with the cost of other lightweight fill materials.
Since tire shreds are lightweight, smaller horizontal stresses
are induced behind a retaining wall constructed with a mixture of soil and tire shreds as the backfill material, compared with a retaining wall having only soil as the
backfill material. Also, tire shred–sand mixtures have relatively high shear strength. Due to these properties, the
width of a retaining wall can be reduced and savings
obtained. In addition, tire shreds are free-draining materials, and thus do not contribute to excessive pore pressure
generation that can cause stability problems during loading
of the backfill material. Based on the results of a full-scale
field test, Humphrey and Eaton (1993) indicated that the
use of tire shreds could also reduce the depth of frost penetration and be a cost effective solution when an insulation
layer is necessary for a given application. However, there
are some concerns regarding the possibility of internal
combustion of fills constructed with tire shreds exclusively,
as observed in Washington and Colorado (Humphrey,
1996), and of groundwater contamination.
Tire shreds have been used as a lightweight fill material
in many embankments and retaining structures in various
US states, including Colorado, Indiana, Maine, Minnesota, Oregon, Vermont, Washington and Wisconsin, and
outside the USA (Bosscher et al., 1992; Humphrey, 1996;
Humphrey et al., 2000; Dickson et al., 2001; Moo-Young
et al., 2001; Khan and Shalaby, 2002; Zornberg et al.,
2004). Seven states (North Carolina, Oregon, Minnesota,
Washington, Colorado, Indiana, and New York) have provisions for the use of tire shreds (Moo-Young et al., 2001).
These studies show that tire shred–soil mixtures have lower
Table 1
Unit weight and cost of various lightweight fill materials
Lightweight material
Unit weight
(kN/m3)
Approximate cost
($/m3)
Shredded tires
Geofoam (EPS)
Wood fiber/sawdust
Expanded shale and clay
Fly ash
5.5–6.4
0.2–1
8–10
3–10
10–14
20–30
35–65
12–20
40–55
15–21
compressibility and higher shear strength and thus perform
better than only tire shreds. In addition, they also show
that the impact of the construction of embankments with
tire shreds or tire shred–sand mixtures on the groundwater
and air quality is negligible.
2. Research objectives
Purdue researchers and Indiana Department of Transportation (INDOT) engineers have cooperated in an active
program to study the use of recyclable materials in the construction of transportation facilities. As a result of this
effort, a demonstration tire shred–soil embankment was
planned and constructed by INDOT in 2001. The test site
is located at State Rd. 31, in Lakeville, IN (USA). The
demonstration embankment is part of a reconstruction
project with the removal of an old bridge. The tire shred–
soil embankment was constructed with an approximate
23/77 weight ratio (50/50 volumetric ratio) of tire shreds
and soil as fill material. In this paper, the results of laboratory tests performed to characterize the engineering properties of the tire shred–soil mixture and the data obtained
from field instrumentation of the test embankment are presented. The instrumentation includes settlement monitoring using settlement plates, vertical and horizontal
inclinometer monitoring, temperature monitoring, and
groundwater quality analysis. The embankment was monitored for a period of 1 y after opening of the roads to traffic. The successful construction and performance of tire
shred–sand embankments, such as the one described in this
paper, will promote the use of tire shreds as a fill material,
with large benefits to society.
3. Engineering properties of tire shred–soil mixtures
3.1. Unit weight
Tire shreds are a lightweight material. The unit weight
of different types of compacted tire shreds, as reported in
the literature, ranges from 2.4 to 7.0 kN/m3 (Humphrey
and Manion, 1992; Ahmed, 1993; Ahmed and Lovell,
1993; Humphrey et al., 1993). These values are approximately 0.1–0.4 times the unit weight of typical soils. The
effect of the compaction energy on the unit weight of tire
shred–soil mixtures is only important for tire shred–soil
mixtures with tire shred contents less than 20% by weight.
The importance of the compaction energy decreases as the
tire shred content of the mixture increases (Ahmed, 1993).
Even though the maximum dry unit weight of tire shred–
soil mixtures increases as the tire shred–soil ratio decreases,
tire shred–soil mixtures are still considered lightweight
when compared with conventional fill materials.
3.2. Hydraulic conductivity
The drainage characteristics of fill materials have
significant influence on the stability of embankments or
S. Yoon et al. / Waste Management 26 (2006) 1033–1044
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retaining structures under saturated conditions. Fill materials with low hydraulic conductivity under a saturated condition may induce slope failures due to the generation of
excessive pore pressures. Compacted tire shreds and tire
shred–sand mixtures have hydraulic conductivity values
ranging from 1.8 · 10 3 cm/s (16% shredded tires by
weight) to 15.4 cm/s (100% shredded tires); these values
are greater than (or equal to) those of typical sand or
coarse gravel (Hall, 1990; Humphrey et al., 1992; Ahmed,
1993; Humphrey and Sandford, 1993; Zimmerman, 1997).
were conducted on field test embankments with tire shred
as fill materials have shown that tire shreds have only a
negligible impact on the environment and on the groundwater quality (Minnesota Pollution Control Agency,
1990; Bosscher et al., 1992; Humphrey et al., 2000). However, in severe conditions, leaching of metals can occur due
to exposure of the metal reinforcements present in the tire
shreds (OÕShaughnessy and Garga, 2000). Under such conditions, zinc is often used as an indicator that leaching has
occurred (Collins et al., 1995; Vashisth et al., 1998).
3.3. Shear strength
3.5. Degradation of tire shreds
The shear strength of a tire shred–soil mixture is affected
mainly by the confining stresses, the tire shred–soil ratio
and the density of the mixture. In mixtures of tire shreds
and sand, the tire shreds have a reinforcing effect (Edil
and Bosscher, 1992; Ahmed, 1993; Foose, 1993; Bernal
et al., 1996). Ahmed (1993) conducted triaxial tests on tire
shred–soil mixtures (tire shred size = 25 mm) with various
mixing ratios. A tire shred–soil mixture ratio of approximately 40:60 by dry weight (65:35 by volume) was reported
to produce maximum shear strength values at low to medium confining stresses. Although the mixing ratio that produces the maximum shear strength varies depending on the
size of the tire shreds, the mixture ratio mentioned above
can be used as a reference in the selection of the tire
shred–soil mixture ratio to be used in the construction of
embankments. Small size tire chips (12–50 mm) are usually
equidimensional and larger size tire shreds (50–305 mm)
are long and flat; their shape has an influence in the resulting stress–strain behavior of the mixtures (ASTM D 627098, 1998).
Degradation of tire shreds can be due to two types of
processes: (1) microbial action and (2) ultra-violet light
exposure. Tires are non-reactive materials. The growth of
micro-organisms is inhibited due to the presence of zinc
oxide, anti-degradants and vulcanization accelerators.
Hence, the attack of micro-organisms on tire shreds has
been found to be minimal (Crane et al., 1975). Recent work
indicates that the effect of micro-organisms on scrap tires is
not well understood and further research into the microbial
processes involved is required (Wallingford, 2005). Carbon
black present in tires blocks the damaging ultra-violet component of sunlight. Surface degradation can be prevented
when tires are kept away from sunlight, placed underwater
or buried underground (Collins et al., 2002).
3.4. Environmental properties
Tires are made of natural and synthetic rubber that contains: (a) organic substances (carbon black, polymers, oil,
paraffin, volatile organic compounds); and (b) inorganic
substances (pigments, fabrics, bead or belt materials, aluminum, barium, chromium, iron, lead, manganese, sulfur,
and zinc) (Moo-Young et al., 2001). Various laboratory
leaching tests have been conducted by many researchers
on shredded tire samples to evaluate the potential environmental problems that they can cause (Minnesota Pollution
Control Agency, 1990; Ealding, 1992; Edil and Bosscher,
1992). It is reported that the pH level can affect the leaching
process. Organic components are found to leach more
freely under neutral conditions, while metals leach more
freely under acidic conditions (Westerberg and Màcsik,
2001). Laboratory leaching tests on shredded tire samples
indicate that both the metallic and organic components
are well below the US EPAÕs (Environmental Protection
Agency) TCLP (toxicity characterization leaching procedure) and EP (extraction procedure) standards and that
tire shreds show little or no likelihood of being a material
hazardous to the environment. Also, various studies that
3.6. Exothermic reactions in tire shred fills
In 1995, exothermic reactions were experienced in three
tire shred fill embankments in Washington (Humphrey,
1996). Ignition can occur due to the rise in temperature
caused by exothermic reactions. Potential causes of initiation of exothermic reactions are as follows: (1) oxidation
of exposed steel wires, (2) oxidation of rubber, and (3) consumption of liquid petroleum products by microbes. Oxidation of exposed steel wires is the primary cause of
exothermic reactions (Humphrey, 1996). Mixing of tire
shreds with soil impedes the oxidation process due to the
reduction in the contact area of the exposed steel wires to
oxygen and the formation of a non-combustible insulating
layer that increases the critical ignition temperature (Wallingford, 2005).
3.7. Optimum size of tire shreds
Tire shred sizes range from 50 to 300 mm. Whole tires or
parts of scrap tires are shredded by shredders equipped
with knives or blades. Usually, multiple passes through a
shredder are required for tire shred sizes less than
300 mm (GeoSyntec Consultants, 1998). It is more expensive to produce and obtain smaller sizes of tire shreds.
For this reason, larger-size tire shreds are more economical
when the goal is to use them as construction materials, but
the engineering properties of the tire shred–soil mixtures
must also be considered.
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3.8. Optimum tire shred–sand mixing ratio
Tire shreds have been used either separately or mixed
with soil. Mixing of tire shreds with soil reduces both the
compressibility and the combustibility of tire shred fills.
As mentioned previously, the occurrence of exothermic
reactions produced by tire shreds has been a very critical
issue in the design and construction of tire shred embankments. The presence of sufficient air in tire shred fills may
have played a role in the ignition process that developed
in the incidents where combustion was observed (Humphrey, 1996). To prevent self-ignition, isolation of the tire
shreds is required. When tire shreds are, on average, floating in a soil matrix, isolation of the tire shreds is practically
guaranteed. Lade et al. (1998) proposed a theoretical formulation for the void ratio of mixtures composed of particles of two different sizes. Their findings can be used for
mixtures of tire shreds and sand. Fig. 1 shows a schematic
diagram of the minimum void ratio of binary packing of
particles. In Fig. 1, the minimum void ratio of a material
composed entirely of tire shreds or entirely of sand is
denoted by emin,ts and emin,s, respectively. When sand
particles are added to the voids of an existing volume of
tire shreds, the sand particles fill the voids between the tire
shreds, and the minimum void ratio of the mixtures
(emin,mix) decreases. This will continue until the voids
between the tire shreds are completely filled with sand particles. When all voids between the tire shreds are filled with
sand particles, any further addition of sand will increase
both the overall volume of the mixture and its minimum
void ratio, as shown in Fig. 1. From this point on, further
addition of sand produces mixtures in which the tire shreds
Fig. 1. Schematic diagram illustrating minimum void ratio arrangements
of binary packing of particles (after Lade et al., 1998).
are on average floating in a sand matrix. This explains why,
on a plot of emin,mix vs. sand content, there is a minimum at
a certain value of sand content.
Ahmed (1993) performed laboratory tests to determine
the maximum dry unit weight of mixtures prepared with
various tire shred–sand mixing ratios. The mixtures consisted of 25-mm tire shreds and Ottawa sand. Using a
vibratory table, the oven-dried sand was densified to obtain
the minimum void ratio, and the maximum unit weight of
the sand was determined after several trials. The sand was
then mixed with tire shreds at different mixing ratios, and
the maximum unit weight of each mixture was determined
in accordance with ASTM D 4253 (Standard test method
for maximum index density and unit weight of soils using
a vibratory table). The sand content of the tire shred–soil
mixtures (by dry weight) varied from 0% to 100% (i.e.,
from pure sand to pure tire shreds). As shown in
Fig. 2(a), the maximum unit weight of the mixtures of tire
shreds and sand increases linearly with increasing percentages of sand (ranging from 4.9 to 18.6 kN/m3) because the
specific gravity GS of the sand is larger than that of the tire
shreds. The specific gravity of the sand and of the tire
shreds is equal to 2.65 and 0.95, respectively.
Using the maximum unit weight results of Ahmed
(1993), the minimum void ratio of the tire shred–sand mixtures was calculated and plotted as a function of the tire
shred content of the mixtures (see Fig. 2(b)). The material
consisting only of tire shreds and the material consisting
only of sand have minimum void ratios of 0.92 (emin,ts)
and 0.39 (emin,s), respectively. As the percentage of sand
increases, the minimum void ratio of the mixture decreases
up to a point where its value is the smallest, as discussed
previously. This happens at a tire shred content of 39%
(by weight), for which the minimum void ratio reaches
the minimum of 0.1. Based on these results, the minimum
sand–tire shred mixing ratio that ensures complete isolation of the tire shreds was determined to be equal to 61/
39 by weight (36/64 by volume) for a nominal tire shred
size of 25 mm.
The optimum mixing ratio, which depends on the shape
and size of the tire shreds, can be determined experimentally. As the shape and size of tire shreds can vary significantly depending on the shredding method and
equipment used, testing of the tire shreds that will be used
in the project is required. In order to estimate the optimum
mixing ratio for projects in which mixtures of tire shreds
and sandy soils will be used as fill material, the following
procedure can be followed:
(1) determine the size of the tire shreds and the shredding
method;
(2) determine the minimum void ratio of mixtures of tire
shreds and sand prepared with various mixing ratios;
(3) select the mixing ratio producing the smallest minimum void ratio, that is, the minimum mixing ratio
that ensures floating of the tire shreds in the soil
matrix.
S. Yoon et al. / Waste Management 26 (2006) 1033–1044
1037
20
Dry Unit Weight (kN/m 3 )
18
16
14
12
10
8
6
4
2
0
0
20
40
60
80
100
Tire Shreds (% Dry Weight)
Fig. 2(a). Maximum unit weight of mixtures of 25-mm tire shreds and sand prepared with different tire shred contents (adapted from Ahmed, 1993).
1.0
0.9
Minimum Void Ratio
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
20
40
60
80
100
Tire Shreds (%)
Fig. 2(b). Minimum void ratio of mixtures of 25-mm tire shreds and sand as a function of the tire shred content of the mixtures by weight (adapted from
Ahmed, 1993).
4. Fill material used in the test embankment
4.1. Tire shreds
Tire shreds meeting the requirements established by the
Indiana Administrative Code, 329 IAC 2-9-3 (1996), which
are described below, were used in the construction of the
test embankment. These tire shreds were substantially free
of loose metal fragments and were reasonably clean and
free from contaminants, such as oil, grease, etc., that could
affect the quality of the groundwater. The attached residual metal pieces extending beyond the cut edges of the tire
shreds were not considered loose metal fragments and were
kept to a minimum. The nominal size of the tire shreds,
which is the size that comprises 50% or more of the
throughput in a scrap tire shredding operation (ASTM
D 6270), was 38 mm. The tire shred lengths varied between
38 and 76 mm. The steel belts in the tires were partially
removed. The total unit weight of the tire shreds delivered
at the site before compaction was equal to 4.9 kN/m3. The
tire shreds used in this project were produced and supplied
by Dillion Tire Recycling Co. located in North Liberty,
IN. The selection of the size of the tire shreds was based
on technical and economic considerations, since the smaller the size of the tire shreds, the more expensive they
become.
4.2. Soil
As required by INDOT specifications (INDOT, 1999), a
B-borrow fill material was used as the soil in the tire shred–
soil mixture. A B-borrow fill material is a uniformly-graded
sand with less than 6% of the particles passing the No. 200
sieve. Fig. 3 shows the grain size distribution of the sand
used in the embankment construction. It is classified as a
poorly-graded sand (SP) according to the Unified Soil
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S. Yoon et al. / Waste Management 26 (2006) 1033–1044
100
Percent finer (%)
80
60
40
20
0
10
1
0.1
0.01
Grain size, D (mm)
Fig. 3. Grain Size distribution of sand used in the test embankment construction.
Classification System (USCS). The total unit weight of this
sand before compaction is equal to 17.5 kN/m3.
4.3. Tire shred–sand mixture
The tire shred–sand weight ratio of the mixture used in
the construction of the demonstration embankment was
equal to 23/77 (50/50 by volume). This mixing ratio was
selected based on material availability at the time of construction and on the recommendations of Bosscher et al.
(1992). Before compaction of the fill material, mixing was
done using a front-end wheel loader with a straight-blade
edge. Special care was taken to mix thoroughly the tire
shreds and the sand in order to produce a reasonably uni-
form mixture. Figs. 4(a) and 4(b) show the mixing of the
tire shreds and the sand, and the placement of the tire
shred–sand mixture, respectively. Construction of the
embankment was inspected quite attentively, lift by lift
(lifts were only 300-mm thick). Mixing using this equipment was effective in the field; no segregation of the two
materials was observed. However, for embankment construction involving large volumes of a tire shred–sand mixture, mixing using two front-end wheel loaders is
recommended (Zornberg et al., 2004). Sieve analysis of
samples collected at different locations and depths in the
field may be performed to evaluate the occurrence of segregation, provided the sampling process generates representative samples.
Fig. 4(a). Mixing of tire shreds and sand.
S. Yoon et al. / Waste Management 26 (2006) 1033–1044
1039
Fig. 4(b). Placement of tire shred–sand mixture.
5. Construction of the tire shred–sand embankment
The tire shred–sand demonstration embankment was
constructed during the months of July and August of 2001
(see Figs. 5(a) and 5(b)). Before construction of the embankment, a test pad was constructed to determine the lift thickness and the number of roller passes required to achieve the
desired unit weight in the field. Based on the laboratory test
results, the optimum moisture content wopt of the mixture
was determined to be equal to 11.5%. The moisture content
of the mixture in the field was maintained a few percentage
points above or below wopt. The degree of compaction of
the test pad was estimated from the weight of the material
delivered and the volume of the compacted materials. Whenever tire shred–sand mixtures are used, measures must be
taken to prevent segregation of the two materials as they
are compacted in the field. Based on the evaluation of the test
pad, a 300-mm-thick lift compacted with six vibratory roller
passes was found to be adequate since almost no deformation or segregation was observed on the compacted layers
of the mixture tested. According to Bosscher et al. (1992),
the use of a vibratory compactor is not recommended for tire
shred–sand mixtures with a high tire shred–sand ratio.
The subgrade was prepared, and a layer of aggregate
base was placed and compacted above it. The aggregate
base was 150-mm thick. A layer of geotextile was laid on
top of the compacted aggregate base as shown in
Fig. 5(a). The geotextile was placed transversely with an
overlap between rolls of 900 mm. The transverse splices
of the geotextile were pinned with hog ring clips. The geotextile layers may provide an additional reinforcing effect
on the sides of the slope and help prevent slope failure at
very shallow depths. However, since the geotextile overlap
between rolls was minimal ( 0.9 m), this reinforcing effect
was not considered in the design of the embankment
slopes.
Fig. 5(a). Schematic cross-section of the test embankment constructed with a mixture of tire shreds and sand.
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S. Yoon et al. / Waste Management 26 (2006) 1033–1044
Fig. 5(b). Location of the settlement plates installed in the embankment (Northeast, Center and Southwest sections).
A 300-mm-thick lift of pre-mixed tire shreds and sand
was then placed on top of the filter fabric. Each layer of
the tire shred–sand mixture was uniformly placed across
the full width of the roadway cross-section. Compaction
of the tire shred–sand mixture was achieved using a D6
10-ton bulldozer with a vibrating steel drum roller. A rubber tire roller was used to spread out the fill material and to
provide additional compaction. Seven layers of the premixed material (tire shreds and sand) were constructed.
The total unit weight of the tire shred–sand mixture
achieved by compaction was monitored by computing the
total weight of the mixture (from a record of the weight
of the tire shreds and the sand used for construction of
the embankment) and the embankment dimensions. The
total unit weight of the tire shred–soil mixture was equal
to 11.5 kN/m3, and the volume of the test embankment
after compaction of the tire shred–sand mixture was equal
to 813 m3.
As shown in Fig. 5(a), the test embankment was covered
with a 0.9-m-thick clay encasement material. The encasement material was placed and compacted at the same time
as the tire shred–soil mixture was placed. Seeding of the
encasement material was then completed.
Based on large-scale direct shear test results, Tatlisoz
et al. (1998) indicated that the friction angle of tire shreds
alone or of mixtures of tire shreds and soil varies from 30
to 54. The slope of the demonstration embankment was
not deemed to be a critical problem due to the large friction
angle estimated for the tire shred–sand mixture used. The
demonstration embankment was constructed with a slope
of 4:1 (H:V). Fig. 6 shows in detail how the geotextile layers were placed in order to form the slope.
1.2 m
0.3 m
1.2 m
1.2 m
0.9 m
1.2 m
0.9 m
1.2 m
0.9 m
1.2 m
0.9 m
0.9 m
0.9 m
0.3 m
0.3 m
0.3 m
0.3 m
0.3 m
0.3 m
Fig. 6. Details of the installation of the geotextile layers on the side of the embankment slope.
S. Yoon et al. / Waste Management 26 (2006) 1033–1044
6. Field instrumentation
Embankment Width (m)
6.1. Settlement plates
Nine settlement plates were installed at three different
depths and in three different sections (Northeast, Center,
and Southwest sections) of the test embankment, as shown
in Figs. 5(a) and 5(b). After the road was opened to traffic,
field monitoring of the settlement plates was conducted for
1 y. The embankment is part of US 31, which is a four-lane
highway. The traffic volume is estimated to be around
22,400 vehicles per day, with 16% of the total volume of
vehicles being trucks. The traffic volume calculated in
equivalent single-axle load (ESAL) is 6,141,497 (assuming
a service life of 20 y and a slab thickness of 225 mm)
(AASHTO, 1993).
The tire shred–sand fill settled as a result of the embankment self-weight and the traffic loads. The data obtained
from monitoring of the upper settlement plates, which were
installed at a depth of 1.2 m from the bottom of the
embankment, are shown in Fig. 7(a). As shown in the
graph, the settlement of the tire shred–sand test embankment was very small. The maximum settlement of the test
embankment after the road had been opened for traffic
for more than 300 days was less than 12 mm. The relative
settlement with respect to the embankment width is equal
to 0.07%. These results show that the settlement was more
or less the same for the three test embankment sections
(Northeast, Center and Southwest) and that it stabilized
after about 200 days of continued traffic. The differential
settlement from surveying observations 1 y after the end
of construction was equal to 4 mm (Fig. 7(a)). This value
matches the data obtained from the horizontal inclinometer measurements fairly well (Fig. 7(b)).
The test embankment was visually inspected periodically
for over a year. During this period, the test embankment
performed well and did not show any visible signs of settlement, lateral movement or erosion. No cracks on the road
or ground surface movements were observed. The embankment slopes retained their original shape. The instrumenta-
Number of Traffic Days
100
200
300
400
Vertical Settlement (mm)
20
0
1041
10
0
-10
-20
0
2
4
6
8
10
77 days
191 days
247 days
12
Fig. 7(b). Horizontal inclinometer measurements.
tion results confirmed that the test embankment performed
well.
6.2. Vertical and horizontal inclinometer
The inclinometer monitoring system consists of an inclinometer casing, a portable digital inclinometer probe and
control cable, and an inclinometer readout unit. As shown
in Fig. 5(a), the vertical inclinometer casing was installed
on the east side of the embankment. Using the vertical
inclinometer measurements, the lateral movement of the
test embankment was monitored after the road was opened
to traffic. The maximum relative lateral movement of the
embankment with reference to the bottom of the embankment was equal to about 2 mm after 42 days of traffic. No
evidence of slope instability or sliding was observed at any
moment.
The horizontal inclinometer was installed in order to
monitor differential settlement in the test embankment.
Monitoring of the horizontal inclinometer was conducted
after 77, 191, and 247 days of road operation. The horizontal inclinometer data is shown in Fig. 7(b). The maximum
vertical settlement observed was equal to approximately
11 mm. This is in agreement with the vertical settlement
data obtained from monitoring of the settlement plates.
These results also indicate that the differential settlement
in the test embankment (about 4 mm) was minimal. This
value matches the data obtained from the horizontal inclinometer measurements fairly well (Fig. 7(b)).
Vertical Settlement (mm)
0
Northeast Side
2
4
6.3. Heat generation
Center
Southwest Side
6
8
10
12
14
Fig. 7(a). Vertical settlement observed as a function of the number of
traffic days.
Heat generation is a critical issue in the design of
embankments made of tire shreds, since the embankments
constructed in Washington and Colorado experienced selfheating (Humphrey, 1996). In the test embankment
described in this paper, however, the fill material was composed of 23% by weight (50% by volume) of tire shreds and
77% by weight (50% by volume) of a sandy soil, such that
complete encasing of the tire shreds with sand was guaranteed. There are concerns that uniformity of the mixtures
cannot be achieved in the field and there might be some
1042
S. Yoon et al. / Waste Management 26 (2006) 1033–1044
localized heat generation within the embankment, which
could potentially cause fires. Fires have only been observed
for embankments constructed entirely of tire shreds (Humphrey, 1996). To our knowledge, there are no reports of fire
occurrences in embankments constructed with tire shred–
soil mixtures.
The temperature inside the test embankment was monitored at the center of one specific section of the embankment for 1 y using a thermometer equipped with an
ANSI (American National Standards Institution) type K
thermocouple probe (see Fig. 5(a)). Fig. 7(c) shows the
temperature variations observed in the test embankment.
As shown in Fig. 7(c), only in the four months around winter time, higher temperatures inside than outside the
embankment (outside air temperature) were observed.
The higher embankment temperature was due to the insulation effect of the fill material. The difference between the
temperature inside the embankment and the outside temperature was, however, small. The highest temperature
observed within the embankment during the monitoring
period was 20 C. This clearly shows that there is no evidence of exothermic reactions. This data confirms the idea
that if tire shreds are combined with soil, internal exothermic reactions do not seem to be a concern. To evaluate spe-
Fig. 7(c). Variation of the temperature with time.
cific exothermic reactions that can cause heating within
embankments, more laboratory studies should be conducted in the future.
6.4. Groundwater monitoring well
To evaluate the impact of the tire shred–sand embankment construction on the groundwater quality, a monitoring
well was installed to a depth of 13.7 m on the southwest side
of the test embankment. The direction of the groundwater
flow was established from borings performed at the embankment site before its construction. The monitoring well was
installed in the direction of groundwater flow in the downgradient to capture the effects of any leaching. During the
well installation, the groundwater level was 11.3 m below
the ground surface. The groundwater quality was monitored
after the road was opened for traffic. The groundwater samples were analyzed for metals using an inductively-coupled
plasma spectrophotometer-atomic emission spectrometry
(ICP-AES) in accordance with standard methods (American
Public Health Association, 1995). Table 2a shows the results
of the water quality analyses performed on several samples
taken from the monitoring well. Table 2b presents the
2001 average rainfall data for Lakeville, IN (National Climatic Data Center, 2004). The groundwater samples were
tested for some selected metals based on the elemental mineral analysis of tire shreds. The results of the groundwater
analyses were compared with the secondary drinking water
standard (EPA, 2002) and the maximum contaminant level
standard for drinking water of the Indiana Department of
Environmental Management (IDEM) (2000).
The public water supply quality was evaluated at Lakeville, IN, by the Indiana Department of Environmental
Management (IDEM) before the demonstration embankment was constructed. The analysis was performed on
May 11, 2000, and its results can be taken as reference.
The results of the groundwater quality analyses performed
on September 5, October 17, and November 21, 2001 show
that all metal levels, except for manganese, are well below
the secondary and maximum contaminant standard levels
Table 2a
Groundwater quality analyses
Contaminant
Unit
Maximum contaminant
level for drinking water
(IDEM)
5/11/2000 (IDEM)
September 5, 2001
October 17, 2001
November 21,
2001
Arsenic
Barium
Cadmium
Chromium
Selenium
mg/L
mg/L
mg/L
mg/L
mg/L
0.05
2
0.005
0.1
0.05
0.0057
0.0565
Limit of detection ion
0.0012
Limit of detection ion
0.0166
0.0943
0.0008
0.0363
Limit of detection ion
0.0148
0.0962
0.0011
0.0551
0.0175
0.0186
0.1132
0.0003
0.0497
0.023 0
9/05/2001
10/17/2001
11/21/2001
0.0478
0.0342
0.0696
Limit of detection ion
0.1891
0.0928
0.0826
0.0175
0.1171
0.0734
0.1649
0.0230
Secondary drinking
water
Aluminum
Iron
Manganese
Zinc
mg/L
mg/L
mg/L
mg/L
0.05–0.2
0.3
0.05
5
–
–
–
–
S. Yoon et al. / Waste Management 26 (2006) 1033–1044
1043
Table 2b
Average rainfall (in mm) in Lakeville, IN (USA), in 2001 (National Climatic Data Center, US)
Jan.
Feb.
Mar.
Apr.
May.
Jun.
Jul.
Aug.
Sep.
Oct.
Nov.
Dec.
Total
80
84
77
93
87
146
132
67
154
79
110
74
1184
for drinking water (IDEM). Manganese, however, does not
represent health concerns (EPA, 2002). The exposed steel
belts, which contain 2–3% of manganese by weight, are
thought to be the source of the manganese in the groundwater samples of other tire shred–soil embankments (Humphrey et al., 2000). Based on laboratory leaching tests, Edil
and Bosscher (1992) noticed that the concentration of manganese increased with continued leaching. To evaluate the
effect of tire shreds on the groundwater quality more accurately, organic materials should also be analyzed in future
research.
7. Conclusions
A tire shred–sand test embankment was constructed at
State Rd. 31, in Lakeville, IN (USA). The fill material
was composed of tire shreds and a sandy soil mixed in
equal proportions by volume. The height, length and width
of the test embankment were about 2.1, 20 and 17.7 m,
respectively. Based on the investigation and monitoring
of the tire shred–sand test embankment, the following
observations and conclusions are proposed:
1. Settlement of the test embankment was monitored for
1 y after opening of the road for traffic using nine settlement plates located at three different sections of the
embankment. After 200 days of road traffic, the settlement stabilized at small values. The maximum settlement observed was approximately 12 mm.
2. Vertical and horizontal inclinometer monitoring was
conducted during the 1-y period following the opening
of the road for traffic in order to check the lateral movement and the differential settlement of the test embankment. The maximum relative lateral movement with
reference to the bottom of the embankment was only
about 2 mm. No evidence of significant differential settlement was observed.
3. Samples of groundwater were analyzed periodically for
metals. Except for manganese, which does not pose a
health concern according to the US EPA (2002), all
metal levels were well below the standard limits prescribed for secondary drinking water (EPA, 2002). They
were also below the maximum contaminant level for
drinking water according to the guidelines of the Indiana Department of Environmental Management
(IDEM, 2000).
4. Temperature measurements were made during 1 y in
order to check for the possible development of exothermic reactions that might lead to the initiation of fires in
the embankment. No evidence of internal heat generation was detected.
5. Floating of the tire shreds in a soil matrix is desired to
prevent self-ignition. The minimum mixing ratio that
produces such an arrangement can be determined by
laboratory tests. Other mixing ratios can be explored
in order to increase the strength of the mixtures.
6. Evidence of slope stability problems, cracking of the
road pavement or erosion was not observed.
Based on the above findings and observations, it can be
concluded that the use of mixtures of tire shreds and soil in
embankment fill construction is very promising and should
be promoted. Performance of the test embankment was
quite satisfactory. Advantages of this material include the
fact that it is lightweight, relatively cheap, easy to compact,
free-draining and relatively incompressible. Additionally,
this use is beneficial to the environment in that a waste
material is recycled. The positive impact of the construction of the test embankment on the local community paves
the way for continued use of tire shreds in civil engineering
applications.
Acknowledgments
This work was supported by the Joint transportation
Research Program administered by the Indiana Department of Transportation and Purdue University. The contents of this paper reflect the views of the writers, who
are responsible for the facts and the accuracy of the data
presented herein. The contents do not necessarily reflect
the official views or polices of the Federal Highway Administration and the Indiana Department of Transportation,
nor do the contents constitute a standard, specification,
or regulation.
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