IMPACT OF REPETITIVE LOADING ON SUBGRADE PARAMETERS DERIVED FROM LIGHT WEIGHT DEFLECTOMETER TEST

The most popular methods used for evaluation of subgrade bearing capacity with light weight deflectometer (LWD) assume linear-elastic behaviour of material. In these methods the input data used for identification of subgrade parameters are limited to initial loading cycles. Change of material parameters occurring under repetitive loading is not taken into consideration. Due to the characteristics of road building materials, including in particular granular materials, omitting the compaction resulting from repetitive loading is considered a rough approximation. Actually the subgrade parameters do change after each load application. It is generally accepted that after the third loading cycle (3rd drop) final degree of compaction is achieved and, as such, the vertical deflections obtained at the fourth, fifth and sixth cycles provide a representative measure of the subgrade parameters (calculated as an average of the three measurements). This paper presents the results of research carried out to verify the above-mentioned assumption by measuring subgrade displacements according to LWD test, followed by comparing the measurement results against numerically identified moduli of the respective layers. The authors have demonstrated that the identified subgrade parameters vary depending on the number of loading cycles (drops) in LWD test. Identification of subgrade parameters was carried out with 3D-FEM (Finite Element Method).