Subgrade and Foundation Dynamic Performance Evaluation by Means of Lightweight Deflectometer Tests

ABSTRACT: The evaluation of the in situ bearing capacity of subgrade and foundation layers in nowadays carried out by means of enhanced dynamic testing devices like the Light Weight Deflectometer (LWD). Those devices presents many practical advantages than traditional plate load tests and allows to simulate the real condition of load induced by the heavy vehicles traffic. The types of devices provided with the load cell and geophone are able to acquire the load-deflection time histories, sampling data every 0.25 ms, with a great level of accuracy. LWD data are mainly used to calculate Surface Modulus of the tested materials by means of Boussinesq equation; more recently some particular procedures, specifically developed to estimate the material compaction level achieved on site, are also starting to be used. This paper regards the use of LWD to investigate performance of subgrade and foundation layers materials in terms of stiffness (bearing capacity) and compaction achieved. Great effort have been devoted to the evaluation of the possibility to enhance deflectometric tests correlating the Energy Loss (energy spent to deflect the tested surface, determined as the area enclosed by the load-deflection graph) to performance of tested material, especially in terms of compaction level achieved on site. Furthermore the influence of load frequency on results obtained have been analyzed and described. Results, obtained on different trial fields, confirm the reliability of LWD in roadwork quality control and for staged design approach to earthworks.