Testing of Contact Stress at Ballast Bed-Soil Subgrade Interface under Cyclic Loading Using the Thin-Film Pressure Sensor

Abstract

Abstract A novel pressure testing method, i.e., a thin-film pressure distribution measurement system, was utilized to investigate the contact area and stress at the ballast bed-soil subgrade interface of conventional railways during cyclic loading in model tests. Factors like the amplitude and frequency of cyclic loading and the existence or nonexistence of the subballast were considered to study their effects on the contact area and average stress over the contact area at the interfaces. In addition, the testing results were compared with those measured by the traditional testing method using earth pressure cells and those calculated by the finite element method (FEM) based on continuum theory. The study shows that, because of the discontinuous characters of the ballast medium, the stress diffused from the ballast bed on the subgrade surface was unevenly distributed but becoming relatively evenly distributed as the subballast was being installed. The subgrade surface stresses measured by the earth pressure cell and calculated by the FEM were very similar, but both were about 50 % lower than the average stress over the contact area measured by the novel thin-film pressure sensor. As the interface stress between the ballast bed and the subgrade is a key factor in subgrade deterioration, new testing methods and numerical calculation methods can consider the discontinuous characters of the ballast appropriately to be necessary for the investigations of the interface contact stress.