Deflection Comparative Study on Subgrades between Falling Weight Deflectometer and Dynamic Load Plate

Abstract

Falling Weight Deflectometer (FWD) and Dynamic Load Plate (DLP) are two survey systems very similar in their concept. In both devices there is a load which falls from a certain height on a plate which is in contact with the ground. The deflection is measured by a sensor placed on the load point. The impact tries to reproduce the passing of a standard axis loaded truck, but in a dynamic and not static way, which is how loads are actually produced on roads. There are variations both in the load and the plate. Also, the FWD has additional sensors, which makes it possible to supply the necessary data to carry out back calculations. However, in the case of subgrades evaluation, the value that is used is the maximum deflection, thus the presence of more sensors does not improve the data acquisition when it comes to the evaluation of subgrades. There is another traditional test included in the Standards to evaluate subgrades which is based on a static load plate. There are several studies trying to establish a correlation between static and dynamic load plate tests. Nevertheless, the fact that there are different types of load (static and dynamic) makes it quite difficult. With regard to this, there are also studies that advise against the use of the static load plate test to evaluate subgrades. In this paper the comparison between these two systems using dynamic loads (FWD and DLP) is analyzed. The maximum deflection comparison has been sought in more than 1500 tests, performed by both devices at the same point and with equal moisture conditions. This number of tests has to be more than enough to find a correlation between the two tests.