Document Details
|
Document Type |
: |
Thesis |
|
Document Title |
: |
Behavior of Granular Bases / Subbases with Fines سلوك طبقات الأساس و تحت الأساس الحصوية ذات المواد الناعمة |
|
Subject |
: |
Faculty of Engineering |
|
Document Language |
: |
Arabic |
|
Abstract |
: |
Flexible pavements has been the predominant type in use in Saudi Arabia roads and other parts of the world, where the majority of paved surfaces fall under the over all category of flexible pavements. Pavements in developed urban areas should be of high performance. Granular base and subbase layers are essential components of a conventional flexible pavement system where their function is to reduce traffic induced stresses in the pavement surface and to minimize rutting in the granular layers and the subgrade. Therefore, characteristics and behaviors of granular base and subbase layers have a major influence in the performance of flexible pavement systems.
Previous empirical methods, based specifically on the California Bearing Ratio test (CBR), have been used to evaluate the properties and behavior of flexible pavement systems. However, concerns about this empirical approach forced highway engineers to develop new techniques to perform dynamic loading tests on granular materials to asses the dynamic response of soil to vehicular traffic.
Resilient Modulus (MR) of the granular materials has been used to characterize its elastic behavior and is being used as one of the main input variables in the analytical procedures used to predict the behavior of flexible pavements. In 1982, the American Association of State Highway and Transportation Officials (AASHTO) established the Standard Method of Test for Subgrade soil AASHTO Designation T 274 -82 . Since then several updates to the testing method were developed, and AASHTO Designation T 307-99 is the latest. The mechanistic-empirical (M-E) design of flexible pavements approach adopted by AASHTO Design Guide 2002 requires specifying MR as the main input property to describe the granular layers.
Fine materials, which is the materials passing sieve no.200, fills the voids between particles in granular aggregate, resulting in lower hydraulic conductivity that decreases exponentially with increasing fines content. On the other hand, excess fines and improper drainage in areas with high ground water table tend to increase water retention of the granular layers and might bring its water content close to saturation level, which in turn reduces its resilient modulus (MR). Moisture sensitivity depends on gradation, nature primarily plasticity index (PI) and amount of fines and the degree of saturation. Gradation of the aggregate, particularly the fines content has been observed as a key factor in the development of permanent deformation, in an aggregate base/sub-base that originates from excess pore water pressures delivered by dynamic axle loads. Also, Conventional asphalt pavements with dense-graded bases showed more fatigue when compared to asphalt pavements with permeable bases [72].
Local experience confirms the above findings, where it was observed that several conventional asphalt pavements with granular base/subbase layers exhibited poor performance in the areas with high ground water table [64].
The main objective of this research is to study the effect of fine contents and degree of saturation on the resilient modulus of granular base and sub base and its effect on the overall performance of flexible pavement.
In this research, an experimental program was conducted to determine the effects of fine content and degree of saturation on MR of granular base and sub base materials.
A triaxial test sample is compacted to maximum dry density at optimum moisture content and at different degrees of saturation. After that, the prepared sample is tested to determine their MR. the AASHTO Standard Method of Testing Designation T 307-99 was adopted. The test result shows that, as the amount of fines is increased the resilient modulus MR is decreased. Also, the test result shows that, as degree of saturation is increased, the resilient modulus MR is increased up to approximately 90 % degree of saturation, after which MR is decreased. Decreasing of the slope of curve is less for 4% fines content and sharper for 16 % fines.
Based on the tests results, a calibrated predictive model of the MR was developed for granular materials with fines.The predicted model shows stress dependency of relating MR with the stress invariant (Ө), the deviatoric stress (σd), degree of saturation (S), and fines contents (passing sieve no. 200). Also, the calibrated predictive model indicates a reasonable value of MR when compared to experimental values. |
|
Supervisor |
: |
Prof. Sabry Ahmad Shihata |
|
Thesis Type |
: |
Doctorate Thesis |
|
Publishing Year |
: |
1430 AH
2009 AD |
|
Added Date |
: |
Wednesday, January 13, 2010 |
|
Researchers
| عبد الله عيسى الزهراني | Al-Zahrani, Abdallah Isa | Researcher | Doctorate | |
|
Back To Researches Page
|