عنوان مقاله [English]
In most asphalt pavements design methods, there is less focus on base and sub-base layers and most of the researches are focused on the asphalt layer. While these layers play an important role to reduce stress on the base layer. The behavior of pavement aggregate layers in short-term and long-term is different and these layers show a complex behavior due to their elastoplastic characteristics. Thus it is important to evaluate their behavior to compare and try out different materials. This leads to select the best material for pavement and the best grading, wet and compaction conditions. Related to above, it is extremely important to select the laboratory condition which can exactly simulate real stress condition applied on the pavement. Portable falling weight deflectometer (PFWD) test is commonly used for assessment of the pavement’s bearing capacity of unbound layers. PFWD test results are modified with multiple variables. Previous studies have demonstrated the effects of different variables on layer stiffness modulus, one by one. In the present study, we tried to find the simultaneous effects of different variables such as sample thickness, wet content, weight, and compaction on base layer surface modulus and deflection. The results of the present study have shown that the fluctuation range of preliminary and modified central geophone was between 90 to 240 μm and 40 to 110 μm, respectively. Moreover, the highest fluctuation of preliminary central geophone was estimated for 20 cm thickness and 20 kg mass weight. In addition, our results have revealed that the range of modified surface modulus was between 175 to 500 MPa which the maximum value was for 97% compaction and 40 cm thickness and the minimum value was for 10 Kg weight in 20 cm thickness. Furthermore, we confirmed that an increase in layer compaction and thickness leads to a decrease in deflection and an increase in mass of weight, though moisture has not influenced the mentioned factor significantly. With regard to the correlation coefficients obtained from all four cases, it is concluded that the choice of the mathematical model adoption, is correct and practical. This study evidenced that each of variables significantly has an effect on the fluctuation of preliminary and modified central geophone as well as a fitted model of modified surface modulus, while moisture, compaction, and thickness have an effect on the fitted model of the preliminary surface modulus.