This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
This RAPID award was made to take advantage of a unique opportunity to add a basic research component to an existing industry testing program that is about to begin. By taking advantage of a project being planned by the Transportation Technology Center, Inc. (TTCI) at their Facility for Accelerated Service Testing (FAST), this research can be accomplished for a small fraction of its costs as a stand-alone research project. The close collaboration with industry also enhances the opportunities for technology transfer.
The research team will investigate the relationship between the dynamic response of sub-track geo-materials to dynamic excitation resulting from train traffic. In particular, the dynamic response will be monitored by six triaxial piezoelectric accelerometers placed in a test section, one in each subsection. The test bed consists of six sections with variations in percent fouling (passing 3/8" sieve) material in the track ballast and the type of tie used in the construction. The purpose of the installation and measurement is to record the acceleration time history when a heavy axle load (HAL) train passes over. Using the power spectral density (PSD), predominant frequencies can be identified. By recording the acceleration time histories over time, the PSD can be compared with the baseline PSD. Changes in the predominant frequencies will relate to the changes in the material behavior of the sub-track geo-materials. The fundamental theory is that as material stiffness changes, the frequency response will also subsequently change. Comparing the change to a baseline conditions would provide an indication of changes in material stiffness. A second part of the research project is to conduct plane strain box tests on the ballast and tie configuration. This is to be done with the same materials used to construct the test section. These tests will be used to evaluate stiffness and deformability of the test section.
The primary objective of the research is to determine if the changes in natural frequency can be correlated to the need for maintenance of the sub-track material and provide a means to predict the need for maintenance prior to the physical manifestation of settlement and deflection that can be measured by conventional means. If successful, this research could lead to a fundamentally new method of evaluating ballast in an automated and continuous process, thereby reducing the number of accidents resulting from ballast degradation.
