*Article* **Identification of Parameters and Fatigue Life Assessment of the Road Pavement Lower Construction Layers under Heavy Construction Traffic**

**Piotr Mackiewicz \* and Bartłomiej Krawczyk**

Faculty of Civil Engineering, Wrocław University of Science and Technology, 50-370 Wrocław, Poland **\*** Correspondence: piotr.mackiewicz@pwr.edu.pl; Tel.: +48-71-320-45-57

**Abstract:** This article analyzes the results of testing the subgrade and the lower layers of the pavement structure with the light weight deflectometer at a load of 0.1 and 0.15 MPa. It is shown that, with layer systems with an equivalent layer modulus lower than 80 MPa, significant nonlinear phenomena occur at a load of 0.15 MPa. In this situation, the identification of a reliable replacement module, a commonly used test method, at a load of 0.1 MPa, is not appropriate—it significantly overestimates the value of the modules (even by 34%), which in turn translates into a significant overestimation of the fatigue life of the structure. In a situation where intensive exploitation of the lower layers of the pavement structure is planned before the final layer arrangement is made, it is required to apply test loads corresponding to the stress conditions occurring in these layers of the structure. Such a situation takes place under the influence of technological (construction) or temporary traffic (substitute, e.g., by-pass) during construction. In order to verify the above assumptions, numerical calculations (FEM) were carried out in the elastic model for layered structures with replacement modules determined in field tests. It was found that, especially in the case of low-bearing layer systems, it is necessary to use correction factors for modules determined with a dynamic plate at a load of 0.1 MPa. Taking into account the corrected values of the modules will allow to correctly determine the change in the durability of layers at the construction stage and in the subsequent operation of the final pavement structure.

**Keywords:** pavement; fatigue; subgrade; modules; FEM; light weight deflectometer
