FACTORS AFFECTING THE MECHANICAL RESPONSE UNDER LOADING OF UNBOUND GRANULAR MATERIALS

Several studies are devoted to the calculation of serviceability life and design of foundation layers of road pavements, which are two of the main concerns of pavement engineering. For comprehension it is fundamental to have a knowledge of the mechanical behaviour of granular materials to reach a satisfactory pavement structural analysis and design. One of the most used parameters is the resilient modulus. The structural analysis starts with the assumption of constant elastic modulus used as an input for the calculation of the internal tensions in order to obtain resilient modulus using regression parameters k1, k2 and k3. By the use of constant Young modulus, the first problem was to verify if such approximation generates valid results. The behaviour of granular materials depends on stresses and moreover it changes properties with the variation of the environmental conditions. Through the analysis of the obtained results, a second problem emerged: the choice of representative points where tensions could be calculated. Indeed, stresses are strictly dependant on the point of calculation and tension results. Instead, with the experimental analysis the resilient modulus was obtained by tests on specimens in which it was tried to reproduce "in situ" conditions. Indeed, specimens were realized with different combinations of density and water content. Supposing to create a representative condition of land, the variations of moisture content, compaction density and loads applied are the main three characteristics that allow identifying six different specimen configurations. Thanks to this, it was possible to understand how to change material behaviour in different conditions. Density effect and influence of water content were analysed for this purpose.