The Springbox is a relatively new piece of equipment, designed to generate realistic values of modulus for use in pavement design. The specimen, which can be of soil, granular or lightly stabilized material, is a 17cm cube, confined by steel sides, two of which are spring-loaded and free to move during the test. Repeated load is applied vertically through a full-face loading plate. Detailed descriptions are given elsewhere, but this paper will include an overview of the equipment. However, the principal content of the paper concerns an evaluation of the true meaning of the test based both on comparisons between Springbox data and on finite element analysis (FE) of the stress conditions within the specimen. The comparative test data are obtained on three different granular materials (Clay soil, Sub-Base and Cement Treated Base). The FE analysis was performed using experimentally obtained values of resilient modulus and Poisson’s ratio and comparing the simulation with the real test in terms of longitudinal and vertical strain in order to assess the FE model. Reference is then made to the FE analysis of the equipment in order to explain the material’s local behaviour inside the specimen with respect to the global mechanical behaviour, which is evaluated during the test by means of point measurements, which are, therefore, assumed to be representative of the stress and deformation state of the material. The model is able to take into account the effect of friction between the steel sides and the material (cf = 0.4), which can highly affect the interpretation of results. Moreover, a FE parametric study was carried out under different static and dynamic load conditions on unbound materials with different characteristics. Finally, conclusions are drawn regarding the potential use of the equipment in generating values of stiffness modulus for design.
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