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.Ibrahim 1* Dr. Gandhi G. Sofia 2* Zaman T. Teama 3 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.