Laboratory study of waste tires fill used with foundations in expansive soils.
Trouzine, Habib ; Asroun, Aissa ; Long, Nguyen Thanh 等
Introduction
In the last years, the use of recycled materials has grown. The new
material has interesting engineering properties and contributes to an
environmental action. The technique of soil reinforced by used tires
called Tiresoil "Pneusol" [1-4] is an instance of such
reinforcements. In addition to the preservation and protection of the
environment, the use of old tires is a cheap means for the conception
and building of various constructions. It is well known that in such
structures, tires have a stress distributor function. This technique can
be used to reinforce embankments, slopes, retaining walls ... This
technique is widely used in France, Algeria, and Canada ... [1-4].
Tires bale is another technique of soil reinforced by bales of
waste tires. Tires bales can be made by a lightweight tire baling
machine and can be used in transportation applications which include,
among others: roadway sub-grade fill, repairing of failed slopes,
improving slope stability, embankments for roadway structures, backfill
material for retaining walls, frost heave mitigation, sound barrier
walls, and rock fall barriers. This technique is experimented and used
in USA, UK, and Australia [5].
TDA 'Tire Derived Aggregate', are waste tires that have
been cut into pieces and are used in range of civil engineering
applications: lightweight fill for highway embankments, retaining wall
backfill, vibration damping layers for rail lines, insulation to limit
frost penetration, drainage layers for landfills, drainage layers for
on-site wastewater treatment systems [6-7]. This technique raises much
interest as it is the subject of many researches undertaken in several
laboratories in the world [7-9].
Full-scale and laboratory experiment of the different applications
of the Tiresoil showed that this material possesses a sufficient bearing
capacity to support a light construction (study of the LCPC (French
Public Works Research Laboratory) and the INSA of Lyon), and that this
material has a significant capacity for absorption of the earth
pressures and waves (study of the INSA of Lyon, of the ENTP of Algiers
and the INI of Tunis), and that the cost of this material is generally
very competitive [3,10,11,12] Why not then consider the utilization of
this material as the foundation of a small building or light works or as
layer of foundation for road on expansive soils [4, 13, 14].
In the field of geotechnical engineering, it has long been known
that swelling of expansive soils caused by moisture change result in
significant distresses and hence in severe damage to overlying
structures. Expansive soils are known as shrink-swell or swelling soils.
Different clays have different susceptibility to swelling. The greatest
problems occur in soils with high montmorillonite content. Such soils
expand when they are wetted and shrink when dried. This movement exerts
pressure to crack sidewalks, basement floors, driveways, pipelines and
foundations. The damages due to expansive soils are sometimes minor
maintenance but often they are much worse, causing major structural
distress [15]
Building on expansive soils requires arrangements that generally
depend on the expansivity of the soil, but these arrangements often
generate some important over costs.
The principle of the current provisions aiming at getting rid of
shrinking and swelling problems of some soils rests on two possible
choices [16]: Either to adapt the structure to the movements of soils;
or to intervene on expansive soil.
This paper presents a qualitative study of a new application of the
Tiresoil that is the Tiresoil under foundations on expansive soils. This
work includes an experimental study on a small-scale laboratory model of
the effects of layers of Tiresoil on the swelling of two sorts of soils;
natural soil in the region of Sidi Bel Abbes, Algeria << Tanera
soil >> and artificial clay << the bentonite of Maghnia
>>.
Bearing capacity of Tiresoil
Load tests with a circular foundation (B = 1.6m) were carried out
on a mass of Tiresoil. The objective of those tests was to compare
bearing capacity and settlement of sand fill and two Tiresoil fills [2].
The test pit was dug on the site with a surface of 230 [m.sup.2].
It has a depth of approximately 3.20m (Fig. 1). The pit was waterproofed
by a plastic cover. A drain surrounded by a Geotextile was installed on
two levels at its periphery.
[FIGURE 1 OMITTED]
Tiresoil was made of four layers of truck tires associated to
Fontainebleau sand (Table 1). Three cases were studied (Fig. 2 and Fig.
3).The load is applied to the slab by means of a hydraulic actuating
cylinder assembled on a mobile carriage which can slide on a retained
beam with each one of its ends by an anchoring tie bean (Fig. 4) [2].
[FIGURE 2 OMITTED]
[FIGURE 3 OMITTED]
[FIGURE 4 OMITTED]
The implementation of each layer of Tiresoil was first carried out
by the installation of the tires which were filled with Fontainebleau
sand by mini bulldozer and spread sand until tires are covered with 10
cm of sand. The next step was the watering of the layer which aimed at
having better compaction. A regular density control had to be observed.
However, for the fourth and last layer it was proceeded differently,
after laying tires, a Geotextile was spread on. Then the tires were
filled with Fontainebleau sand to cover them under 40 cm. The watering
of the layer was undertaken still only one half of the fill is compacted
as a mean of comparison and control the density.
One type of foundation was used for the load tests. It is a
circular footing with 2 [m.sup.2] surface (1.6 m diameter) and a 20 cm
thickness. t is made out of reinforced concrete with its part a higher
steel plate 30mm thickness and 1 m diameter allowing centering of the
kneecap and the base another plate of steel 10mm thickness, whose object
is to ensure a smoothen contact between foundation and soil. The load
was applied in a progressive way to the foundation by stages, until
settlement of the foundation from 15 to 20 cm, each stage being
maintained during 30 minutes or more.
During the loading, three parameters were controlled:
--The applied load; deduced from the pressure of the fluid in the
jack.
--The foundation settlement, located by 4 incremental position
sensors.
--The vertical movements of the surface of the soil near the
foundation.
Fig. 5 shows the evolution of the creep A and the settlement S (mm)
according to the pressure [q.sub.0] in the two cases studied compared to
the case of sand alone
The curves of settlement/creep of sand present a traditional
aspect, a parabolic pace progressively with the increase in the loading.
The two tests on Tiresoil give nearly the same results as that of sand
(Fig. 5) [2].
[FIGURE 5 OMITTED]
Under a fill height of approximately 0.4 m, "the mixture"
is about homogeneous. The settlement due to the loadings presents a
first linear part then grows more quickly [2].
Even if the bearing capacity of Tiresoil is equal to half of that
of sand, it is however far from being negligible. It is moreover more
largely sufficient to support a work (house for example). Moreover the
coefficient of creep is also a little weaker. Such a structure would be
settled in shorter time [2].
Settlement and absorption of pressure of Tiresoil
The tests are carried out in a cylindrical tank of 1500mm of
diameter and 600mm of depth (Fig. 6). The used soil is Hostun RF sand.
All the experiments were carried out with polyurethane tires on the
scale 1/20 compared to a truck tire [3,12].
[FIGURE 6 OMITTED]
The layers of Tiresoil (three layers at least in order to ensure
the periodicity of material) are laid out the ones on the others in
double quincunx with a shift of a semi-diameter, without thickness of
sand between them. Each layer covers a square surface of 780mm. The
loading is applied with a rigid metal slab of 350mm of diameter and 35mm
of thickness. The fill is vertically charged up to 123 kPa, by stage of
20 kPa. It is subjected to several cycles of loading/unloading. Each
test is repeated three times. Measurements of the pressures are taken
with total pressure transducers disposed under the Tiresoil. Identical
measurements are carried out on referential sand fill, charged under
similar conditions [12].
The study consisted in examining the influence of the thickness of
Tiresoil fill on the distribution of the pressures under the foundation.
The comparative study of the results had been based on the Factor of
Absorption of Tiresoil (FAP). This factor is the ratio of the vertical
pressure under the Tiresoil foundation to the vertical pressure in the
referential sand fill (sand alone) [12].
FAP = [P.sub.Tiresoil]/[P.sub.Sand alone]
Fig. 7 presents the distribution of the total constraints in the
referential sand fill and under the Tiresoil fill containing three
layers of tires.
It is noted that: Whatever the fill, the form of the distribution
is convex. However, the convexity of the curves with Tiresoil is less
marked.
The pressures are maximum under the central vertical axis of the
slab, and minimal close to the edges. The curves of distribution of the
pressures are spread out much in the presence of Tiresoil. These
observations also checked for Tiresoil fill respectively made up of 5 -
7 and 9 layers of tires show that the distribution of the pressures is
done in a more homogeneous way in the presence of Tiresoil.
[FIGURE 7 OMITTED]
Indeed, in these fills, the gradient of the pressures (difference
between the minimal and maximum pressure) is lower than that obtained in
the sand fill alone (referential fill) [12].
The influence of the Tiresoil fill on the distribution of the total
pressures under the slab is illustrated still better by the curves of
evolution of the FAP (Factor of Absorption of Tiresoil) presented on
Fig. 8 per three layers of tires [12].
[FIGURE 8 OMITTED]
Under the center of the slab, the FAP is quasi-constant for each
load; its value varies between 0.6 and 0.8 thus representing a fall from
20 to 0% of the constraints compared to the referential fill.
Under the edges of the slab, the FAP increases gradually until a
maximal value of approximately 1.3 which corresponds to the maximum
loading of 120 kPa, this increase of nearly 30%.
Fig. 9 and 10 show the evolution of the FAP according to the number
of layer constituting the Tiresoil fill (3 - 5 - 7 and 9 layers) under
the axis and the edge of the foundation slab.
[FIGURE 9 OMITTED]
[FIGURE 10 OMITTED]
It is noted that the FAP decreases notably under the center of the
slab (Fig. 9). Beyond three layers, its value remains ranging between
0.6 and 0.8. This reduction of 20 to 40% of the pressures was also
noticed on the central pressure transducers close [12].
Under the edge of the slab (Fig. 10), the FAP remains ranging
between 0.9 and 1.1 for the first four increments of load, with a light
tendency to increase according to the number of layers. For the last two
increments (100 and 120 kPa), the FAP increases clearly and can reach
1.5, thus representing a significant rise of the pressures generated
under the edges of the foundation slab.
The results confirm the stress distributor effect of Tiresoil
foundation. Beyond 3 layers of tires, whatever the depth the influence
of the Tiresoil is characterized by an important diminution of the
pressures under the central part of the slab, between 20 and 40% and an
important increase of the pressures under the edges.
Those different results clearly point out the mechanical function
of the Tiresoil, which consists in the distribution of the loads
outwards the influence area of the slab. The cycle effect on the
Tiresoil material is characterized by a number of rheological
modifications [17].
Tests with expansive soils
This phase of research was aimed to design a small-scale laboratory
model and to carry out a series of tests to check its operation in order
to calibrate it, and to put in evidence the Tiresoil ability to absorb
the swelling of clays. The principle of the test is to determine the
variation of volume due to the swelling of reconstituted clay, in the
time, and charged vertically, and then to compare it to when Tiresoil is
arranged in sandwich between the load and the expansive clay. Five cases
have been investigated. In the two first cases (referential tests), only
the expansive soils were used to observe the vertical swelling
displacements.
As it is well known, larger stresses are created if the expansions
of soil are prevented. Therefore, to reduce the transmitted swelling
pressures to underground structures and/or retaining walls, a
compressible material can be inserted between expansive soils and the
structures so that when the expansive soil swells, the compressible
material would be compressed and less swelling pressure would result
[22].
In the third case, one layer of Tiresoil as a compressible material
with a thickness of 30mm was inserted between the load and the first
expansive soil (Tanera soil). In the fourth case, Tiresoil with a
thickness of 30mm was used with the second expansive soil (Bentonite),
and finally two layers of Tiresoil with a thickness of 60mm were
inserted between the vertical load and the Bentonite.
Materials and methods
The tests are carried out in a cylindrical tank of 455mm of
diameter and 445mm of depth (Fig. 11). It is covered by a circular plate
with porous stones. The diameter of the plate is slightly less than the
one of the vat to permit it to move vertically when the soil swells. The
plate is surrounded by a joint that assures a certain tightness to avoid
all infiltration of the test material and this in order to avoid all
parasitic effects.
During 71-day period, vertical displacements data were recorded.
[FIGURE 11 OMITTED]
Soils investigated
Two soils of different origins and physical properties were
selected. One of the soil samples was obtained from the site located in
Tanera in Sidi Bel Abbes in north-west of Algeria. Some serious problems
caused by large upward and downward movements of the underlying soil
have been observed on many buildings and road pavements. Especially
light structures have been badly cracked. The second soil sample was a
bentonite manufactured by Bental factory in Maghnia in the northwestern
of Algeria.
These two soils were subject to several laboratory identification
tests using standard procedures adopted by the American Society for
Testing and Materials [18-21] and whose results are shown in Table 1.
The literature contains a considerable number of empirical
techniques for assessing the swell potential of soils. From these
experimental results, the swell potential can be estimate of the two
soils (Table 2).
Although the chosen site (Tanera soil) has a reputation of being
very swelling soil, our sample seems to have a weak potential of
swelling to means for classifications of Holtz, Dakshanamurthy and
Raman, 1973; Snethen, 1980; BRS, 1980, it can be due to the taking away
of the soil or to the modification of the soil microstructure when
reconstituted.
The reconstitution of the soil in the test tank was as follows,
after elimination of all soil particles with a diameter superior to 2mm,
soils were drying to a constant weight between 105[degrees] C and
110[degrees] C, then drain was disposed to the bottom of the test vat
and covered by a cardboard sheet of 0.088 g/[cm.sup.2] of surface
density. The expansive soil is placed in to the test vat and compacted
layer by layer at moisture content of 11%. Another sheet of cardboard is
disposed. Loading with 100 kg during 24 hours, 84 kg of load was
discharged for referential tests, and (84 + number of layers of Tiresoil
x 6) kg, for tests with Tiresoil. (The applied constraint in all studied
cases is of about 0.015 kg/[cm.sup.2]). The test tank was placed then in
a water bath and remained submerged in water, during 71day period,
vertical displacements were recorded. At the end of all tests moisture
content was about 92% and 98% for expansive soils and 99% for sand
Tiresoil, which can be considered as saturation.
Tiresoil fill
The Tiresoil is arranged by layer on the expansive soil. An
anticontaminant sheet of cardboard is arranged between the soil and
Tiresoil.
The reduced tires are polyurethane crowns which have a scale 1/20
as compared to truck tires. The same crowns used by the INSA of Lyon,
the ENI of Tunis and the ENTP of Algiers for all tests on reduced models
of the other applications of Tiresoil.
The used sand is obtained from the career of Sidi Ali Benyoub in
Sidi Bel Abbes with a maximal diameter of 1mm and minimal diameter of
0.315mm, its humid density is 1.4. The mass of sand is 4000 g/layer.
Tiresoil fill so organized is formed of one to two layers of tire (48
tires / layer), disposed circularly with a shift of about a half
diameter. The mass of the fill is about 6000 g/ layer (Table 3). A
photograph of Tiresoil preparation is given in Fig. 12.
[FIGURE 12 OMITTED]
Results and discussions
Referential tests (no Tiresoil)
These first tests allow the tracing of reference curves in order to
compare them with the other studied cases. Let's note G the
potential of swelling of the soil.
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]
Where:
[V.sub.i]: initial volume of the soil.
[V.sub.f]: final volume of the soil.
[h.sub.i]: initial height of the soil.
[h.sub.f]: final height of the soil.
The mechanism of swelling is complex and is influenced by a number
of factors: the type and amount of clay minerals present in the soil,
the specific surface area of the clay, structure of the soil and the
valency of the exchangeable cation [23].
For tests with no Tiresoil, it is observed that measured vertical
swelling displacements increased with time, as shown in Fig.13. The
displacements reached maximum swelling displacement. Then, they were
decreased slightly. After that, they remained almost constant as found
in the work of Ikizler et al, 2007. The diagrams are given for periods
since the measured vertical swelling displacements remained almost
constant. At the end of the test, the maximum measured vertical swelling
for Tanera soil was about 1.06%. The moisture content of Tanera soil was
11% at the beginning of test; it was 92% at the end of test.
For the bentonite, the clay swells to 11.89%. The swelling of the
Bentonite was distinctly longer in time than the Tanera soil (Fig. 13).
The final moisture content of the bentonite was 98%.
[FIGURE 13 OMITTED]
The maximum swell of bentonite is of about 13.6 more significant
than the Tanera soil. These results confirm what was stated by the
literature concerning the swell potential. The maximal swelling
variation of the volume remains relatively weak compared to oedometric
tests; this can be due to the height of the soil, because the more the
height of the soil increases, the more swelling decreases. This
reduction is due to the lateral frictions against the tank.
Tests with Tiresoil
Laboratory test results--expansive soil with 1 layer of Tiresoil
In the third and fourth test set up, one layer of Tiresoil with a
thickness of 30mm was inserted between the load and expansive soil. At
the beginning of test, the moisture content of Tanera soil and Bentonite
was 11%; the Tiresoil was completely dry. Fig. 14 shows the measured
vertical swelling with time. The percentage of swelling reduction
"[DELTA]G/G (%)" is calculated in table 4.
The Tanera soil with Tiresoil settles about 1.1% with a swelling
reduction of 226.44%. This very large value is due to the fact that the
soil of Tanera has a low swell potential. At the end of test (71 days
after) the moisture content of Tanera soil was 95%; for Tiresoil,
moisture content of sand was 99% and 13% for tires. The final Tiresoil
thickness can be calculated by the formula:
[h.sub.f] = [h.sub.i] + [DELTA]h - [DELTA][h.sub.a]
Where:
[h.sub.f]: final thickness of Tiresoil.
[h.sub.i]: initial thickness of Tiresoil.
[DELTA]h: thickness variation of the expansive soil with Tiresoil.
[DELTA][h.sub.a]: thickness variation of expansive soil alone
(referential tests).
[FIGURE 14 OMITTED]
The calculated final thickness of Tiresoil reported to referential
test is about 27mm For the test with Bentonite with one Tiresoil layer
(Fig 15), the maximum vertical displacement was measured about 0.39%.
Note that the vertical swelling was reduced 96.72%. At the beginning of
test, the moisture content of expansive soil was 11%, Tiresoil was
completely dry. After 71-day periods the moisture content was 98% for
the bentonite, 99% for sand Tiresoil and 13% for tires. The calculated
final thickness of Tiresoil reported to referential test is about
16.2mm.
[FIGURE 15 OMITTED]
Laboratory test results--expansive soil with 2 layers of Tiresoil
For this test setup, only the thickness of Tiresoil was different.
In this case two layers of Tiresoil with a thickness of 60mm were
inserted between the vertical load and expansive soil. The measured
vertical swelling potential with time is shown in Fig. 15. The measured
maximum vertical settlement is -0.93%; with 107.82% of swelling
reduction.
The moisture content of expansive soil at the beginning of test was
11% with a completely dry Tiresoil. At the end of the test (71 days
after) the moisture content was 98% for expansive soil, 99% for Tiresoil
sand and 13% for tires.
The calculated final thickness of Tiresoil for this test is about
44.62mm.
Conclusions
The two techniques adopted to build on expansive soils are; either
the stabilization of the clay (mechanical, thermal, or chemical
stabilization), or the adaptation of the structure to the expansive soil
(respect of construction rules on the levels of the infrastructure, the
structure, purification and the peripheral protection of the
evaporation). Other techniques of stabilization are in phase of study as
the use of used tire-chips mixed with clayey soil [24].
The suggested technique in this research consists in the adaptation
of the infrastructure to expansive soil by disposition of a compressible
material (Tiresoil) between foundations and expansive soil. For the case
of the roadways, Tiresoil can be a shape layer between the roadway and
the soil.
The basic purpose of this investigation is to determine the
potential decrease in swelling as a result of the inclusion of Tiresoil
with different thicknesses placed between an expansive soil and a rigid
foundation using an experimental setup.
For this purpose, two swelling soils were placed and compacted in
an experimental device in a controlled laboratory environment. To
examine the potential for reducing vertical swelling of these soils,
Tiresoil with different thicknesses were placed between foundation and
expansive soil in experimental test tank.
The experimental results indicate that the reduction of swelling is
related to the Tiresoil thickness as well as to the swell potential of
soil (pressure of swelling). For the same Tiresoil thickness (1 layer),
in the case of the Tanera soil, clay with a low swell potential, no
swelling was noted but a settlement with a very significant reduction of
swelling of 226.44%. For the bentonite, clay with a very high swell
potential (Montmorillonite), the recorded reduction is 96.72% less than
half of the value recorded for the Tanera soil.
If Tiresoil layers number is doubled, Bentonite with Tiresoil
settle with a reduction of swelling of 107.82%, an increase in the
reduction of swelling compared to the test with only one layer of
approximately 11%.
It's noted that for all tests the Tiresoil thickness decrease.
An attempt to exploit and adapt the principles of homogenization to
simulate the behavior of Tiresoil under foundation on expansive soils is
being studied. To control this technique full-scale tests and tests with
several cycles of swelling and shrinking should be done.
References
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Habib Trouzine (a,b), Aissa Asroun (b) and Nguyen Thanh Long (c)
(a) Sciences et Modelisation, Institut de Mathematiques de
Bordeaux, France. Email: h_trouzine@yahoo.fr
(b) Laboratoire de Materiaux et d'Hydrologie; Departement de
Genie Civil, Universite de Sidi Bel Abbes, Algeria. Email:
a_asroun@yahoo.fr
(c) Laboratoire Central des Ponts et Chaussees Paris, France.
Email:Pneusol@yahoo.fr, h_trouzine@yahoo.fr Fax: +33 558 57 46 43 Phone:
+33 610 70 94 33
Table 1: Some properties of the used sand
Properties Sand
Coefficient of uniformity Cu 1.90
Coefficient of concavity Cc 1
Maximum dry unit weight [[].sub.d OPN] (kN /[m.sup.3]) 15.4
Optimum moisture contents [W.sub.OPN] (%) 16
Minimal dry density 1.35
Maximal dry density 1.65
Specific gravity 2.6
Table 2: Some properties of the investigated soils
Properties Soil of Tanera Bentonite
Liquid limit (%) 31 133
Plastic limit (%) 17 50
Shrinkage limit (%) 11.5 9
Plasticity index (%) 14 83
Specific gravity 1.17
Grains sizes
Gravel (%) 0 0
Sand (%) 25 20
Silt (%) 27 18.8
Clay (%) 48 61.2
Methylene blue values
Volume of blue [V.sub.B] ([cm.sup.3]) 8 42.7
Specific surface SST ([m.sup.2]/g) 168 897
Table 3: Swelling-shrinkage potential soils as assessed by the
different classifications
Tanera soil Bentonite
Altmeyer (1955) Critical High
Holtz, Dakshanamurthy Low to moderate --
et Raman (1973)
Snethen (1980) Low Very high
Building Research Low to moderate High to very high
Establishment (1980)
Table 4: Some properties of the Tiresoil
Sand tire Tiresoil
Number /layer 48
Mass (g) /layer 4000 2000 6000
[D.sub.min] (mm) 0.315
[D.sub.max] (mm) 1
Table 5: Reduction of the final swelling of the Tanera
soil and the Bentonite in the presence of Tiresoil fill.
Tanera soil
G (%) [DELTA]G/G (%)
Only Clay (referential test) 0.87 --
Clay with 1 layer of Tiresoil -1.1 226.44
Clay with 2 layers of Tiresoil -- --
Bentonite
G (%) [DELTA]G/G (%)
Only Clay (referential test) 11.89 --
Clay with 1 layer of Tiresoil 0.39 96.72
Clay with 2 layers of Tiresoil -0.93 107.82
