Highway Research Record

VI. RESEARCH WORK DONE IN ACADEMIC INSTITUTIONS RELATED TO THESIS WORK
B. PAVEMENT ENGINEERING AND PAVING MATERIALS
A Study on the Evaluation of Granular Layer Moduli for Flexible Pavements

Date of Start:May 2004
Indian Institute of Technology, Kharagpur (S,I)

Scope and Objectives
(i) To experimentally study the behaviour of granular material under different states of stress.
(ii) To develop a finite element program for pavement analysis
(iii) To develop models for estimating effective moduli for granular layers for different combinations of layer thicknesses,       subgrade strength and wheel loads.
(iv) To evaluate experimentally the effect of moisture and fines on the resilient modulus of the granular layer.

Methodology
Granular material with WMM gradation was chosen for testing. Repeated triaxial tests were conducted on the material to determine the stress dependence of the modulus of the material. Different combinations of deviator stress and lateral stress were used for evaluating the resilient modulus of the material. The generalized constitutive model (NCHRP1-28A) proposed in the AASHTO 2002 draft design guide was used to characterize the material. The material was also modeled according to the K-Theta model. Additional repeated triaxial tests were conducted by varying the moisture content in the material and also by varying the fines content.
ANSYS package was used to conduct finite element analysis of typical pavement structure. A macro has been developed that conducts iterative analysis of the pavement structure after modifying the modulus values of the granular layer elements each time, according to the stress values obtained from the previous iteration. The iterations were continued until the desired convergence in the modulus values was obtained and then the responses in terms of surface deflections at seven radial locations were obtained.

Findings and Conclusions
(i) The resilient modulus value of granular material was found to be significantly affected by the state of stress, presence of     moisture and presence of fines.
(ii) The effective modulus of the granular layer has been found to be a function of different pavement parameters like      subgrade strength, bituminous layer strength and layer thicknesses.