Investigation of the effect of loading pulses on the ballast resilient modulus with SmartRock in a large-scale triaxial test

Abstract

Ballast resilient modulus is a key metric for assessing track resiliency and guiding railroad maintenance. Large-scale triaxial tests are used to determine the ballast resilient modulus and mechanical properties. Replicating complex train-induced loading pulses from field observations in a laboratory setting is challenging owing to technical limitations. Consequently, laboratory tests often employ simplified half-sine and haversine loading pulses with various rest intervals to simulate real-world conditions. However, the effects of different pulses on the obtained ballast resilient modulus remain unclear. In this study, large-scale triaxial tests were conducted using SmartRock sensors to investigate the effects of various cyclic loading pulses on the resilient modulus of the railroad ballast. A new index, called the cyclic loading duration ratio (CLDR), was introduced to categorize these pulses. The results revealed that the resilient modulus correlated with the CLDR, with its impact contingent upon the deviator stress. A CLDR value of 0.20 emerged as a critical threshold, yielding the lowest resilient modulus. Values below this threshold resulted in an increased resilient modulus owing to the consequential large axial acceleration. This study provides insights into the micromechanical resilience reactions of railroad ballast under diverse loading pulses and offers guidance for pulse selection in triaxial testing.