Finite Element Modelling of Asphalt Concrete Pavement...

International Journal of Materials Chemistry and Physics

Vol. 2, No. 2, 2016, pp. 62-70

http://www.aiscience.org/journal/ijmcp

Finite Element Modelling of Asphalt Concrete Pavement Reinforced with Geogrid by Using 3-D Plaxis Software

Mohammed Abbas Hasan Al-Jumaili*

Department of Civil Engineering, Faculty of Engineering, University of Kufa, Najaf City, Iraq

Abstract

This paper studied the application of 3-D Plaxis software on reinforced asphalt concrete pavement with geogrid layer at two

positions within the pavement structure to investigate effect of geogrid on the critical pavement responses such as total stress

and vertical surface displacement. An axisymmetric finite element model was loaded with an incremental cycling contact

pressure from 50 to 600 kPa and the geogrid layer was placed either at the bottom of surface asphalt concrete or at top of

subbase course to study influence of geogrid position on pavement performance. The analysis results indicated that under

various tire pressure values, a significant effect on the pavement behaviour was observed when the geogrid layer was located at

bottom of asphalt concrete surface layer. The Plaxis output results also showed a moderate improvement in pavement system

response was obtained when geogrid reinforcement layer was placed at top of subbase layer.

Keywords

Asphalt Concrete, Georid, 3-D Plaxis and Vertical Displacement

Received: January 9, 2016 / Accepted: January 27, 2016 / Published online: February 16, 2016

@ 2016 The Authors. Published by American Institute of Science. This Open Access article is under the CC BY-NC license.

http://creativecommons.org/licenses/by-nc/4.0/

1. Introduction

The high modulus polymer geogrid has been utilized within

the asphalt concrete courses during the past few decades to

enhance flexible pavement behaviour and its performance .

The geogrid will resist the fatigue stress and strain at bottom

of asphalt concrete course due to it has the tensioned

membrane effect. The Geogrid-reinforcement layer can be

placed at the sub base - sub grade interface or between the

base course and sub-base to to reduce total rutting failure at

pavement surface [1]. The use of geogrid reinforcement in

construction of highway pavement started in the 1970s. Then,

the technique of geogrid reinforcement has been increasingly

used and many experimental and analytical studies have been

performed to assess geogrid behaviour in the flexible

pavement [2, 3, 4, and 5].

Pandey et al. [6] studied a two dimensional axisymmetric

FE model was used to analyse the response of geogrid

reinforced bituminous pavement subjected to static and

dynamic loading. They found that the fatigue (horizontal)

stain reduced when geogrid was placed at base -bituminous

concrete interface. The results showed that placing geogrid

layer at the interface of base and subgrade layers caused the

highest reduction in vertical strain. Barksdale et. al. [7]

investigated the structural performance of unreinforced and

geogrid reinforced pavement subjected to laboratory

cycling loading testing. The vertical permanent deformation

was measured of both unreinforced and geogrid reinforced

pavement. The results indicated the stiff geogrid placed at

the bottom of granular base did not give any significant

improvement for a strong pavement whereas the placing the

geogrid at bottom of the base layers resulted in better

performance (low permanent deformation) than the use of a

geotextile. They carried out FE simulation analysis

techniques and showed that the benefits of geosynthetic

reinforcements are more pronounced for weaker subgrades.

Moayedi et. al. [8] used the FE PLAXIS program to study the

effect of geogrid reinforcement in flexible pavement by

developed the axisymmetric pavement response model under

International Journal of Materials Chemistry and Physics Vol. 2, No. 2, 2016, pp. 62-70 63

static loading condition. Bituminous concrete layer and

geogrid were modeled as a linear elastic isotropic material

while the Moho-Coulomb material model was adapted to

represented granular base materials. They obtained that the

geogrid reinforcement placed at the bottom of bituminous

concrete layer reduced vertical pavement deflection.

Hamdy and Ahmed [9] studied a series of FE simulations by

Plaxis software on suggested pavement structures consisted

of asphalt concrete layer, base layer, subbase layer on

subgrade layer.They concluded a significant improvement in

pavement behavior by placing one –layer of geogrid

reinforcement where the vertical displacement and effective

stresses are lower in case of one geogrid layer or two

geogride layers.

In the present study, an attempt has been made to investigate

the influence of geogrid reinforcement at two positions

within the asphalt concrete system through the application of

3-D Plaxis software program. The geogride reinforcement

layer was firstly placed at bottom of surface asphalt concrete

layer and secondly the geogrid was placed at top of granular

subbase layer to investigate.

2. Finite Element Model

The flexible pavement system used in 3-D PLAXIS software

version 2013 consisted of asphalt concrete (AC) surface

layer, asphalt concrete (AC) base layer, granular subbase

layer and sandy subgrade layer subjected to repeated cycling

loading with 0.10 second loading period. The unreinforced

and geogrid reinforced pavement response was evaluated

under a repeated cycling loading (50, 100, 150, 200, 250,

300,350,400,450,500,550 and 600 )kPa acting on a circular

area of 0.15 m radius with frequency of 10 HZ which is

corresponding to 0.1 seconds duration . A triangular wave

with duration of 0.1 second corresponding to an average

speed of around 70 km/h was adopted in this study [10]. The

duration time between two subsequent axles is assumed to be

0.2 second.

The two asphalt concrete layers and geogrid were modeled as

a linear elastic isotropic material while the Mohr-Coulomb

model was used to model granular subbase and subgrade

materials.

An axisymmetric model was utilized in the analysis using

45900-noded structural solid elements with medium

refinement. Axisymmetric modeling was chosen in this study

because it could simulate circular loading and did not require

excessive computational time [2, 11].

Alex [12] indicted that the nodal radial strains were assumed

to be negligible at approximately10 times R (radius of loaded

area) from the area applied wheel load. Also, the nodal

stresses and displacements were assumed to be negligible at

20times R below the pavement surface. Therefore, the width

and the length of the model were set at 5m, and the total

thickness of model is 4m. Total pavement structure thickness

is 0.45 m above sandy subgrade depth of 3.55 m. The

thickness of AC surface course is 0.05 m, the thickness of AC

base course is 0.10 m while the thickness of granular subbase

course is 0.30 m as shown in Figure 1.

Figures 2 through 3 show the model considered in this study

and it was input borehole in 3-D Plaxis software with the

cycling repeated wheel load and these figures indicate the

placement of geogrid at bottom of asphalt concrete surface

course and at top of subase course reactively.

Fig. 1. Cross section of the selected pavement structure

64 Mohammed Abbas Hasan Al-Jumaili: Finite Element Modelling of Asphalt Concrete Pavement Reinforced

with Geogrid by Using 3-D Plaxis Software

Fig. 2. FE axisymmetric model considered for reinforced pavement at bottom of asphalt concrete surface layer.

Fig. 3. FE axisymmetric model considered for reinforced pavement at top of subbase layer.

Since the resilient modulus test equipment is not currently

available in many laboratories, researchers have developed

correlations to converting CBR values to approximate MR

values. The correlation considered reasonable for fine

grained soils with a soaked CBR of 10 or less is [13]:

MR (MPa) = 10.3 * (CBR) (1)

The minimum limit of CBR value of subgrade will be taken

as 4% in accordance with Iraq specifications requirements

(SCRB /R5) [14]. Therefore, resilient modulus of subgrade

can be calculated from eq.(1) and it is founded as 40 MPa.

Claessen et al. [15] established the relation between subbase

resilient modulus and subgrade resilient modulus according

to the following relationship:

MR= 0.2 * h0.45

* MR (subgrade) (2)

Where

h = the thickness of subbase layer in mm.

In this study, the thickness of subbase layer is 300 mm and MR

for the subgrade was 40 MPa and as a result the MR value of

subbase course is 100 MPa. Material parameters and

constitutive models used are shown in Table (1) whereas Table

(2) shows mechanical properties of geogrid reinforcement.

Table 1. Pavement materials properties.

AC Surface AC Base Grave and sand Subbase Sand Subgrade

Model Linear elastic Linear elastic Mohr-Coulomb Mohr-Coulomb

Thickness(m) 0.05 0.1 0.3 2.55

Young’s modulus(MPa) 4000 3000 100 40

Poisson’s Ratio 0.35 0.35 0.45 0.45

Dry density(kN/m3) 23 23 20 17

Saturated density (kN/m3) --- --- 22 20

Cohesion(kN/m2) --- --- 20 8

Friction angle (degree) --- --- 40 35

Dilatation angle (degree) --- --- 15 5


Table 2. Physical and mechanical properties of Netlon CE121 product.

Physical properties

Property Result

Mesh type Diamond

Standard color Black

Polymer type HDPE

Packaging Rolls

Dimensional properties

Property Unit Result

Aperture size mm 6*8

Mass per unit area g/m2 740

Rib thickness mm 1.6/1.45

Junction thickness mm 2.75

Rib width mm 2/2.75

Mechanical properties

Peak tensile resistance kN/m 6.4

Elastic modules GPa 0.39

Tensile strength MPa 9

Percentage elongation at maximum load % 6

3. Results and Analysis

In this section repeated cycling loading condition is presented

for both unreinforced and geogrid-reinforced base. Applied

contact pressure ranged from 50 kPa to 600 kPa and geogrid

was placed at two positions either at bottom of asphalt

concrete surface layer or at the interface of asphalt concrete

base layer and subbase course. Critical pavement responses

i.e. total stress and total vertical displacement of unreinforced

and geogrid reinforced pavements are determined under for

each contact pressure value.

Figures 4 through 6 illustrate the vertical displacement

profile for applied contact load of 600 kPa for case of

unreinforced pavement and reinforced pavement with one

layer of geogrid placed either under AC layer or above

subbase layer.

Fig. 4. Vertical displacement contour for unreinforced pavement (applied tire pressure =600 kPa).



Fig. 5. Vertical displacement profile for reinforced pavement with geogrid at bottom of AC surface layer (applied tire pressure =600 kPa).

Fig. 6. Vertical displacement contour for reinforced pavement with geogrid at top of subbase layer (applied tire pressure =600 kPa).

It may be observed from above figures that a significant

decrease in vertical settlement obtained for reinforced

pavement at both of bottom of AC surface layer or top of

subbase layer. Maximum vertical displacement is 4.213x10-3

m for case of unreinforced pavement, while it is -3.518x10-3

m and -3.675*10-3

m for reinforced AC surface and at top of

subbase pavement courses respectively. It can be concluded

that the reduction in vertical displacement (rutting) at

pavement surface by 16.5% when geogrid was placed at

bottom of AC surface course.

Figures 7 to 9 illustrate the total stresses profiles for applied

tire pressure of 600 kPa for case of unreinforced pavement

and reinforced pavement with geogrid placed under AC

surface layer and at top of subbase layer respectively.


Fig. 7. Total stresses contour for unreinforced pavement (applied tire pressure = 600 kPa).

Fig. 8. Total stresses contour for reinforced pavement with geogrid at bottom of AC surface layer (applied tire pressure = 600 kPa).



Fig. 9. Total stresses profile for reinforced pavement with geogrid at bottom of surface layer (applied tire pressure = 600 kPa).

Figures 6 through 8 indicated that for unreinforced pavement,

maximum total stress (335.9 kPa) is significantly higher

compared with that for case of reinforced pavement with

geogrid at bottom of surface layer (118.8 kPa) and reinforced

pavement with geogrid at top of subbase layer (224.5 kPa).

Figures 10 and 11 show comparison between pavement

system behaviour for three cases: unreinforced pavement,

geogrid reinforced pavement at bottom surface layer, and

geogrid reinforced pavement at top of subbase layer. The

three cases are compared in regards of total stress and

vertical settlement responses

Fig. 10. Maximum vertical displacement values of unreinforced and geogrid reinforced pavements.


Fig. 11. Maximum total stress values of unreinforced and geogrid reinforced pavement.

Regardless of applied pressure values, the pavement with

geogrid reinforcement at bottom of AC surface layer has a

slightly lower maximum vertical displacement and total

stress than that of other cases as shown in Figures 10 and 11.

4. Conclusions

Based on 3-D Plaxis software outputs applied on pavement

structure to evaluate the benefits of reinforcing pavement

with geogrid at two positions, the following conclusions can

be drawn:

1 A significant improvement in pavement behavior is

obtained by placing geogrid layer at bottom of asphalt

concrete surface layer. Vertical displacement and effective

stress responses are significantly lower for reinforced

pavement system in comparison with unreinforced

pavement.

2 Moderate improvement in pavement system behavior was

gained by adding geogride at top of subbase layer.

3 The best location of adding geogrid within the pavement

structure is near to applied tire pressure within the asphalt

concrete layers.

4 The use of geogrid significantly enhances the resistance of

asphalt concrete to the deformation and development of

cracking failure.

References

[1] Pandey, S., Rao, K. R. and Tiwari, D. (2012). Effect of geogrid reinforcement on critical responses of bituminous pavements. 25th ARRB Conference –Shaping the future: Linking policy, research and outcomes, Perth, Australia.

[2] Howard, I. L. and Warren, K. A. (2009). Finite-element modeling of instrumented flexible pavements under stationary transient loading. J. Transportation Eng. ASCE, 135 (2): 53-61.

[3] Perkins, S. W. (2001). Mechanistic-empirical modeling and design model development of geosynthetic reinforced flexible pavements. Montana Department of transportation, Helena, Montana, Report No. FHWA/MT-01-002/99160-1A.

[4] Perkins, S. W. (2002). Evaluation of geosynthetic reinforced flexible pavement systems using two pavement test facilities. Report No. FHWA/MT-02-008/20040, U.S. Department of Transportation, Federal Highway Administration.

[5] Berg, R. R., Christopher, B. R., and Perkins, S. W. (2000). Geosynthetic reinforcement of the aggregate base course of flexible pavement structures. GMA White paper II, Geosynthetic material Association, Roseville, MN, USA, 130 p.

[6] Perkins, S. W., Ismeik, M. and Fogelsong, M. L. (1999). Influence of geosynthetic placement position on the performance of reinforced flexible pavement systems. Proceedings of the Conference Geosynthetics ‘99, Boston, MA, USA, Vol. 1, pp. 253-264.

[7] Barksdale, R. D., Brown, S. F., and Chan, F. (1989). Aggregate base reinforcement of surfaced pavement. Geotext. Geomembrane, 8, pp. 165–189.

[8] Moayedi, H., Kazemian, S., Prasad, B. and Huat (2009). Effect of Geogrid Location in Paved Road Improvement. Journal of EJGE, Vol.14, pp.3313-3329.

[9] Hamdy, F. and Ahmed M. H. (2014). 2D Plaxis finite element modeling of asphalt-concrete pavement reinforced with geogrid. Journal of Engineering Sciences Assiut University Faculty of Engineering, Vol. 42No. 6, November 2014, pp. 1336–1348.

[10] LCPC-SETRA. (1997). French Design Manual for Pavement Structures .Paris: Laboratoire Central des Ponts et Chaussées and Service d’Etudes Techniques des Routes et Autoroutes.



[11] Kazemian, S., Barghchi, M., Prasad, A., Maydi, H. and Huat, B.K. (2010). "Reinforced pavement above trench under urban traffic load: Case study and finite element (FE) analysis", Journal of Scientific Research and Essay Vol. 5 (21), Nov.4, 2010, pp. 3313-3328.

[12] Alex, A., (2000). Characterization of Unbound Granular Layers in Flexible Pavements. Report No. ICAR/502-3, Texas Transportation Institute.

[13] AASHTO, (1993). AASHTO guide for design of pavement structure–1993. The American Association of State Highway and Transportation Officials, Washington, D.C.

[14] SCRB/R9, (2003). General Specification for Roads and Bridges, Section R/9, Hot-Mix Asphalt Concrete Pavement. Revised Edition. State Commission of Roads and Bridges, Ministry of Housing and Construction, Republic of Iraq.

[15] Claessen, A., P. Edwards, P. Sommer, and P. Uge, (1977). Asphalt pavement design: the SHELL method. Proceedings Fourth International Conference on the Structural Design of Asphalt Pavements, the University of Michigan, Ann Arbor, Michigan, USA.

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