A preliminary study into dynamic non-linear elasto-visco-plastic modelling of soil mechanics simulated using light weight deflectometer data

The rational structural design, construction and maintenance of a conventional ballasted railway track requires a suitably calibrated computational model of the railway trackbed system. Such a model facilitates design by enabling train induced stresses, strains and displacements to be computed at any point in the track system and for the purposes of construction and maintenance it allows for the back-calculation of the material properties of an existing track. Data from the Falling (FWD), and Light Weight, Deflectometers (LWD), representing the behaviour of the railway track under traffic-like simulated load, are being increasingly used to develop and calibrate these computational models. However, when material properties back-calculated from LWD/FWD data are compared to material properties back-calculated from different tests (e.g., cone penetrometer test or plate load test) the results are not in agreement.
Thus, the first part of this paper discusses the rheological properties of several mechanical models of material behaviour proposed in the literature to be utilized within the LWD and FWD methodology. The review argues that in order to replicate material behaviour more closely there may be a need for a new mechanical model for use within the FWD / LWD methodology, which would combine non-linear elasto-visco-plasticity and dynamics. In the second part of the paper, a preliminary one dimensional form of such a model is presented. The rheological properties of the model, created by combining impact mechanics models and non-linear plastic models, are explained and the results of its calibration using LWD data are given. From the results, it is shown that in order to calibrate the material constants of the permanent part of the model both LWD deflection data and LWD load data need to be measured until the deflection stabilizes after the drop.