Novel assessments on dynamic behavior of unbound materials by means of deflectometric tests

The evaluation of the in situ bearing capacity of soils and unbound layers is moving from traditional plate load test (PLT) to enhanced dynamic testing devices, like the Light Weight Deflectometer (LWD), able to provide many practical advantages and to better simulate the real stress levels induced by the heavy vehicles. The type of devices provided with the load cell and geophone allows to acquire the load-deflection time histories, sampling data every 0.25 ms. LWD data are mainly used to calculate Surface Modulus of the soil by means of Boussinesq equation using the peak of applied load and the correspondent peak of centerplate deflection; more recently some special procedures, specifically developed to estimate the material compaction level achieved on site, are also starting to be used. The experimental results presented in this paper analyze the possibility to deeply investigate the dynamic behavior of unbound materials using the information related to load-deflection time histories, focusing attention on the amount of energy spent to deflect the soil. This parameter, usually reported as Energy Loss, represents the area enclosed by load-deflection graph (Hysteresis Loop) and is generally considered an index of the dynamic response of the soil to applied loads. The paper reports the analysis of different correlations between Energy Loss and soil stiffness parameters developed with the aim to investigate the potential use of the Energy Loss for Qc/Qa activities. Results confirm the reliability of this parameter as a quality indicator of soil conditions, providing a wider range of information when compared to standard bearing capacity tests.