Evaluating Flexible Pavement Deformation Over Sand Subgrades

Journal of Environment and Earth Science www.iiste.org
ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online)
Vol.4, No.14, 2014
78
An Approach in Evaluating of Flexible Pavement In Permanent
Deformation OF Paved AND Unpaved Roads Over Sand Dunes
Subgrade Under Repeated Loads
Dr. Saad F.Ibrahim1*
Dr. Gandhi G. Sofia 2*
Zaman T. Teama3
1* B.Sc., M.Sc., PhD (C.E.).MISSMGE.M.I.ASCE, College of Engineering.,Al-Mustansiria University, Iraq,
drsaadfarhan@yahoo.com
2* B.Sc., M.Sc., PhD (C.E.), College of Engineering.,Al-Mustansiria University,Baghdad, Iraq,
gandhisofia@gmail.com
3* B.Sc., M.Sc.(C.E.).College of Engineering.,Al-Mustansiria University, Iraq
alitalaz@yahoo.com
Abstract
Thickness of flexible pavement play very important factor in cost of construction of road ,in this study effect of
change thickness of pavement on rutting of road is investigated . Two approaches are adopted; the first is the
laboratory tests through simulation of three layers of paved road and two layers for unpaved road, using a steel
box with dimensions of 600mm length 500mm width and 400mm depth. Sand dunes are used as a subgrade layer
to investigate its behavior by using it as a part of flexible pavement structure under repeated load at relative
density 55.7%. The effect of change in thickness of asphalt layer in permanent deformation is also investigated,
through using three models at three different thicknesses, starting from zero (unpaved), 50mm and 100 mm. The
second approach is the development of a three-dimensional finite element model for flexible pavements using
ABAQUS (6.12-3) to simulate the laboratory test The results indicate that increase in the thickness of flexible
pavement to 50mm from zero (unpaved), increases the number of passes about 971.42%, while the increase of
thickness from 50mm to 100 mm, increases the number of passes by 517.33%. The results of ABAQUS program
are very close to results of laboratory tests.
Keywords: Sand Dunes subgrade, Thickness of Flexible Pavement, ABAQUS Models
INTRODUCTIO
Flexible pavement layer in construction of roads consider as highest cost and more strength than other layers in
paved road, asphalt layer carry the major part of the traffic loads and reduce the stress which progressive to
subgrade to reduce the distress in pavement body .so it's necessary to study the effect of existing asphalt layer in
ability of road to carry traffic load over sand dunes subgrade. Sand dunes cover large area of Iraq so it's
necessary to investigate the behavior of paved and unpaved road over sand dunes subgrade. During construction
and operation of roads or highways on sand dunes bed may encounter several problems. Some of the associated
problems are mentioned ;A)The real problem of sand dunes is their crawl that affects development of
projects.Sand Dunes cause a decrease in the efficiency and an increase in the maintenance costs for these
projects. The delay of work in a highway between Diwaniyah and Nasriyia is a good example for that (Salem,
2011), B) the formation of depressions and settlement of road (Aiban,1994), C) Shallowness of the ground-
water in some parts (Fookes and H igginbottom,1975) which alters the compressibility of the soil and can lead to
fines migration , D)Variability in strength and compressibility leading to differential settlement (Abu-Taleb and
Egeli, 1981; Al-Amoudi et al., 1991) E)Sand movement causes abrasion to the existing structures and blockage
of some streets and highways. This presents an unacceptable risk in normal practice and calls for the
improvement of the geotechnical properties of such soils prior to any construction (Aiban et al., 1996).
2. RESEARCH METHODOLOGY
2.1 Subgrade
Laboratory experimentation is done to investigate effect of change relative density of sand dunes subgrade
2.2 Subbase Course
The sub base is brought from Al_ Nibaee quarry, north of Baghdad, this type of sub base is commonly used as a
layer in flexible pavement construction.
2.3 Surface course
50-60-penetration grade bitumen is considered for experimentation and aggregates Confirming midpoint
gradation of grade II specifications as per Iraq specification have been used.
2.4 Laboratory pavement setup
Laboratory based pavement sections with conventional materials and that with one value of subgrades relative
density is prepared , subbase layer and surface course is prepared in a prefabricated box type arrangement made
of mild steel of size 600mm length X 500 mm width X 400 mm depth.

Vol.4, No.14, 2014
79
Three Laboratory based multi-layer sample pavement sections were formed, one of them pavement section
with sand dunes subgrade at relative density 55.7% ,subbase and thickness of flexible pavement Zero
(unpaved ) mm symbol , other one of one of them pavement section with sand dunes subgrade at relative
density 55.7,subbase and thickenss of flexible pavement 50 mm and last one same models but with flexible
pavement thickness 100mm.
3 DATA ANALYSIS
3.1 Material Properties
Table 1 show properties of sand dunes which used, table 2 show properties of subbase layer and table 3 show
properties of asphalt layer which used
Table 1: Properties of sand dune
Property Type properties Index
Value
Standards
GS Specific
gravity(G.S)
2.67 ASTM: D -854 -
02L.L Liquid Limit
(L.L. %)
25 ASTM: D -4318-
00P.L Plastic Limit
(P.L. %)
NP ASTM: D -4318-
00PI Plasticity Index
(PI %)
NP
γ max Modify
Compaction
18.7
kn/m3
ASTM 698-00
γ min minimum dry
density
12KN/m3
Soil
Symbols(USCS)
SP-SM (USCS).
Table 2: Properties of Subbase
Chemical Element Result %
So3 2.26
gypsum 4.87
Tss 2.12
Om 1.69
Maximum density 2200
Soil classification GP
Table (3) Properties of asphalt cement
Property
ASTM Designation
Number [16]
Asphalt Cement
Daurah (40-50)
Penetration (25°C, 100 gm., 5sec),
(1/10 mm)
D-5 43
Softening Point (Ring and Ball), °C D-36 51.5
Ductility, cm D-113 > 100
Flash Point (Cleave land open-cup) D-92 335
Specific Gravity , 25 °C D-70 1.048
Loss on heat (5 hrs, 163 °C, 1/8"), % D-1754 0.18
3.2 Laboratory based multi-layer pavement
The thickness of the pavement layers have been designed to ensure that the stresses reach the subgrade level. It
was proposed to form the multi-layer sample pavement section with the 0,50mm and 100mm thick bituminous
concrete, 100mm thick subbase layer and 200 mm thick as show in figure 1and Figure 2 depict the laboratory
pavement.

Journal of Environment and Earth Science
Vol.4, No.14, 2014
Figure 1 Cross section multi
4-FINITE ELEMENT MODELING
4.1 Model geometry
FEA has been proven suitable for application to complex pavement problems. 3D mode was built by using the
finite elements program ABAQUS (6.12
displacements in the entire pavement layers when different densities of subgrade layer, (3D
that has the capacity to simulate actual vehicle loading conditions and estimate the structural response for
flexible pavements are used to simulate laboratory models. The thickness of layers are same thickness of
laboratory are 200mm sand dunes subgrade , 100 subbase and 50 mm and 100mm asphalt ,as shown in Figure
(3). Elastic properties (modulus of elasticity and Poisson’s r
Figure (3): General Geometry
Layers
Asphalt layer
Subbase layer
Subgrade very loose layer
Subgrade
loose layer
Subgrade medium layer
0948 (Online)
80
Figure 1 Cross section multi-layer pavement section
FINITE ELEMENT MODELING
finite elements program ABAQUS (6.12-3), to understand, with more precision, the
displacements in the entire pavement layers when different densities of subgrade layer, (3D
are used to simulate laboratory models. The thickness of layers are same thickness of
(3). Elastic properties (modulus of elasticity and Poisson’s ratio) are shown in Table (4)
Figure (3): General Geometry of the Pavement Layers by ABAQUS Program
Table (4) material properties
Layers Modulus of Elasticity
(MPa)
Poisson’s ratio(
Asphalt layer 1200 0.35
Subbase layer 110 0.35
very loose layer 2 0.3
Subgrade
loose layer
2.5 0.3
Subgrade medium layer 2.7 0.3
www.iiste.org
3), to understand, with more precision, the distribution of the
displacements in the entire pavement layers when different densities of subgrade layer, (3D-DFEM) program
are used to simulate laboratory models. The thickness of layers are same thickness of
of the Pavement Layers by ABAQUS Program
Poisson’s ratio( )*

Vol.4, No.14, 2014
81
4.2 Finite Element Types and Mesh Size
All the parts of the model are modeled using the 8-node continuum three dimensional brick element (C3D8R)
with reduced order numerical integration available in ABAQUS (6.12-3). This element has the capability of
representing large deformation, geometric and material nonlinear Solid element (C3D8R) has three degrees of
freedom at each node. . All layers are simulated with the same shape to preserve the continuity of nodes
between consecutive layers (Massod, 2013). Figure (4) shows total model
Figure (4 )Mesh of All Layers
Boundary Condition
The boundary conditions have a significant influence in predicting the response of the model, the bottom surface
of the subgrade and sides of layers is assumed to be fixed, that means that nodes at the bottom of the subgrade
and sides of layer cannot move horizontally or vertically. This represents the bottom and sides of steel box.
Figure (5) shows the boundary conditions used in the analysis
Figure (5) the Boundary Condition

Vol.4, No.14, 2014
82
4.3 Moving Load
The wheel load applied in the ABAQUS is 96 kg (0.96 KN) and is distributed uniformly over the total contact
area. The resulting uniform contact pressure is 550 MPa which is equal to the pressure of tire which used two
parameters, longitudinal and transverse distribution of vertical pressure on loaded area (Al-Qadi and Wang Hao
2009). Loading is applied to simulate wheel horizontal motion in a pre-determined speed. In this method, loading
position should be moved in a gradual form in order to have a complete wheel rolling as shown in Figure
(6).Figure (7) show wheel path in model
Figure (6) Schematic Illustration of Tire Moving along Pavement Surface
Figure (7) show wheel path
5 RESULTS
Wheel tracking device was used to evaluate the rut depth. These laboratory based pavement were subjected to
wheel tracking on the wheel-tracking device under a contact pressure of 550 MPa and temperature 50 cº result
indicate when thickness of pavement change from zero to 50 mm the ability of pavement structure to carry
traffic loads increase by about 971.42% this value show the effect of flexible pavement in increase capacity of
pavement structure to carry traffic loads while the increase thickness of flexible pavement from 50mm to 100
mm increase ability of pavement to carry traffic loads by about 517.33% Figure (8) and (9) show pavement
surface profile for subbase and subbase/subgrade interface for unpaved model. Figure (10 to 12) show flexible
pavement surface profiles, flexible pavement/subbase interface and subase /subgrade interface respectively for
model with asphalt thickness 50mm .Figure (13 to 15) show flexible pavement surface profiles, flexible
pavement/subbase interface and subase/subgrade interface respectively for model with 50mm thickness for
model with asphalt thickness 100 mm.

Vol.4, No.14, 2014
The results of ABAQUS program are very close to results of laboratory tests, Figure 16 and 18 shows the
ABAQUS out displacement (rutting) .figure 17 and 19 show shows the Result of Lab and ABAQUS for 50mm
and 100mm asphalt thickness respectively. Figure 20 and 21 show the statistical analysis of two models to find
the effectiveness of ABAQUS program in simu
Technique. Figure 22 show the relation between rut depth and number of passes at different flexible pavement
thickness. When thickness of flexible pavement increase traffic benefit ratio incre
is defined as the ratio of the number of passes necessary to reach a given rut depth for model with specific
pavement thickness , divided by the number of passes necessary to reach this same rut depth for control model
with the same subgrade properties. Figure (23) shows the relationship between thickness of flexible pavement
and number of passes at 6 mm rut depth. Figure (24) shows the relationship between rut depth and thickness of
flexible pavement at constant number of pass
passes in unpaved model.
Figure (9) Surface Profile of Subbase /Interface
-30
-25
-20
-15
-10
-5
0
5
0 5 10
Rutdepthinmm
0948 (Online)
83
the effectiveness of ABAQUS program in simulation laboratory models using Graphical Technique, histograms
thickness. When thickness of flexible pavement increase traffic benefit ratio increase as shown in Table (5).TBR
e same subgrade properties. Figure (23) shows the relationship between thickness of flexible pavement
flexible pavement at constant number of passes, the number of passes 55 which represent the max number of
Figure (8) Surface Profile of Subbase
Figure (9) Surface Profile of Subbase /Interface
10 15 20 25 30 35 40 45 50
Width of Steel container in cm
www.iiste.org
lation laboratory models using Graphical Technique, histograms
ase as shown in Table (5).TBR
e same subgrade properties. Figure (23) shows the relationship between thickness of flexible pavement
es, the number of passes 55 which represent the max number of
50
n=0
n=3
n=55
n=37
n=12

Vol.4, No.14, 2014
84
Figure (10) Flexible Pavement Surface Profile for 50mm Asphalt Thickness
Figure (11) Asphalt /Subbase Interface Profile for 50mm Asphalt Thickness
Figure (12) Subbase/Subgrade Interface Profile for 50mm Asphalt Thickness
-30
-25
-20
-15
-10
-5
0
5
0 5 10 15 20 25 30 35 40 45 50
Rutdepthinmm
n=185
n=250
n=270
N=140
n=0
N=110
N=172
n=280
n=365
n=410
n=22
n=40
n=55
-20
-15
-10
-5
0
5
10
0 10 20 30 40 50
Rutdepthinmm
Width of steel container in cm
n=0
n=280
n=410
n=185
n=365
n=90
n=245
-14
-12
-10
-8
-6
-4
-2
0
0 10 20 30 40 50
Rutdepthinmm
N=410

Vol.4, No.14, 2014
85
Figure (13) Flexible Pavement Surface Profile for 100mm Asphalt Thickness
Figure (14) Asphalt /Subbase Interface Profile for 100mm Asphalt Thickness
Figure (15) Subbase/Subgrade Interface Profile for 100mm Asphalt Thickness
-7
-6
-5
-4
-3
-2
-1
0
1
0 5 10 15 20 25 30 35 40 45 50
Rutdepthinmm
n=88
n=120
n=176
n=0
n=89
n=222
n=463
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
0 10 20 30 40 50
Rutdepthinmm
n=463
n=0
n=222
n=283
-1.8
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0 10 20 30 40 50
Rutdepthinmm
n=463

Vol.4, No.14, 2014
Figure (16): ABAQUS output of displacement side for 50mm asphalt thickness
Figure (5.17): The Result of Lab and ABAQUS
Figure (18): ABAQUS output of Displacement for 100mm asphalt thickness
0
5
10
15
20
25
30
0 100
Rutdepthinmm
0948 (Online)
86
Figure (5.17): The Result of Lab and ABAQUS for 50mm asphalt thickness
100 200 300 400
number of passes
www.iiste.org
for 50mm asphalt thickness
500
lab.
ABAQUS

Vol.4, No.14, 2014
87
Figure (19): The Result of Lab and ABAQUS for 100 mm Asphalt Thickness
Figure (20) Histogram of Rutting in Lab. vs. Rutting in ABAQUS for 50mm asphalt thickness
Figure (21) Histogram of Rutting in Lab. vs. Rutting in ABAQUS for 100mm asphalt thickness
0
1
2
3
4
5
6
7
0 100 200 300 400 500
permanentdefformationin
mm
number of passes
lab
ABAQUS
0
5
10
15
20
25
30
ruttinginmm
Different number of passes
Lab.
abaqus
0
1
2
3
4
5
6
7
Ruttinginmm
Different number of passes
lab
abaqus

Vol.4, No.14, 2014
88
Figure (22) the Relation between Rut Depth and Number of Passes at Different Flexible Pavement Thickness
Table (5) Traffic Benefit Ratio TRB
Model type TBR
S3-0-M CONTROL
S3-50-M 7.45
S3-100-M 66.14
Figure (23) the Relationship between Thickness of Flexible Pavement and Number of Passes
0
50
100
150
200
250
300
350
400
450
500
0 1 2 3 4 5 6 7
Numberofpasses
Rut depth at surface in mm
0 cm(unpave)
10cm
5 cm
0
50
100
150
200
250
300
350
400
450
500
0 20 40 60 80 100 120
Numberofpasses
Thickness of flexible pavement in mm
rut 6mm

Vol.4, No.14, 2014
89
Figure (24) the Relationship between Thickness of Flexible Pavement and Number of Passes
5 CONCLUSIONS
Increase in the thickness of flexible pavement increases the number of passes which reaches the same value of
rutting (value of failure) and leads to decrease the displacement in subgrade and subbase layers. ABAQUSE
program was successful in simulation pavement structure models, so ABAQUS program can use in analysis of
paved road.
REFRENCES
• Abu-Taleb, M.G. and Egeli, I. (1981): "Some Geotechnical Problems in the Eastern Province of Saudi
Arabia." Proc., Symp. Geotechnical Problems in Saudi Arabia, King Saudi Arabia, Vol. I, 799-811
• Aiban, A. S. (1994): ''A Study of Sand Stabilization in Eastern Saudi'' Department of Civil Engineering,
King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia Received 24 March 1993;
revised version accepted 5 July 1994
• Aiban, S., Al-Amoudi, O., Asi, I.M. and Zahrani, A. (1996):"Chemical Stabilization of Ras AL-Ghar
Sabkha Soil", Twelfth Southeast Asian Geotechnical Conference, Kuala
• Al-Amoudi, O.S. and Abduljauwad, S.N (1991): " Geotechnical Considerations on Field and Laboratory
Testing of Sabkha." Proc., Symp Recet Advances in Geotechnical Engineering III, Singapore, Vol. 1, 1-6.
• Al-Qadi and Wang H:'' Pavement Damage Due to Different Tire and Loading Configurations on Secondary
Roads'' USDOT.(2009).
• ASTM D854-00: "Standard Test Method for Specific Gravity of Soil Solids by PycnometerLumpur,
Malaysia, Vol. May, pp. 265-270
• Fookes, P. C. and Higginbottom, I. E. (1975): "The Classification and Description of Nearshore Carbonate
Sediments for Engineering Purposes. " Geotechnique, 2, 406-414
• Masood , G.G. ''Experimental and Numerical Investigation of stabilized unbound Granular Pavement
Materials'' AL-Mustansiriya University College of Engineering Highway and Transportation Engineering
Department Ms. Thesis(2013):
• Salem L. A. (2011): '' An Approach in Evaluating The Behavior of Dune sand Under Shallow Footing'' Ms
Thesis University of Baghdad, College of Engineering
• STM D698-00a: "Standard Test Methods for Laboratory Compaction Characteristics of Using Standard
Effort (600 kN-m/m).
0
5
10
15
20
25
30
0 20 40 60 80 100 120
Rutdepthinmm
Thickness of flexible pavement in mm
n=55

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