) FWD( ارزيابي سازه اي آزادراه تهران -قم با استفاده از دستگاه افت وخيز سنج ضربه اي

Structural Evaluation of Tehran-Qom Freeway using a Falling Weight Deflectometer

Determination of modulus of elasticity of various layers of pavements helps in determining the pavement condition and drawing up an effective rehabilitation strategy. In this research 18 Km long section of Tehran - Qom freeway was structurally evaluated by using a PHOENIX FWD. Part of the testing was carried out on the existing pavement and part of these was performed on a section that had been recently recycled using a cement and foam bitumen stabilization technique. Data were analysed by using two programs; namely KENLAYER and Back Calculation Analysis, which are two pre-defined methods that determine elastic modulus of the various layers. From the above analysis it was revealed that there is no strong correlation between the elastic modulus values obtained by the above two methods. This discrepancy was recognized to be mainly due to difference between two major parameters, namely, the reference temperature and the equivalent single axle loads, which are different in the two methods. Calculating the above differences and other minor discrepancies such as geophone positioning in FWD equipment, it was revealed that the overlay design and pavement life predictions achieved in these systems could not be reliable. Alternatively, a Back Calculation Compromise method was proposed. This resulted in more reliable values of the modulus of elasticity of the various layers.