Using of LWD test results to evaluate the pavement granular material and provide empirical models for determining the modulus.

The performance of unbound granular layers, such as base and subbase, is evaluated by various methods. Non-destructive test equipment such as LWD is an appropriate method that, in addition to increasing the speed and accuracy in comparison with destructive methods, evaluates the structural properties of unbound granular material properly. The most important output parameter of the LWD is a modulus that influences various factors such as inherent and massive properties of unbound granular material. In this research, the LWD modulus was determined in different conditions using aggregates based on Grain No. 5 of 234 code. For this purpose, compaction, moisture content, stress level and saturation level were selected as factors affecting the unbound granular material modulus. Using the response surface method, the intended experiments were designed. The results of the experiments showed that the compaction-moisture model has a better interpretation than compaction-saturation and moisture-saturation models, and the interaction of compaction and moisture has a significant effect on the LWD stiffness modulus. Also, the results showed increasing in the modulus of LWD in the form of exponential correlation due to increasing of LWD weight. Finally, the compaction-moisture model was compared with other similar models and it was found that the coefficient of determination of the proposed model is significantly higher than other models and, unlike other models, has a compaction-moisture parameter explaining the interaction effect of compaction and moisture on the LWD modulus.