Publication Details

Indraratna, B., Nimbalkar, S., Navaratnarajah, S. K., Rujikiatkamjorn, C. & Neville, T. (2014). Use of shock mats for mitigating degradation of railroad ballast. Sri Lankan Geotechnical Journal - Special Issue on Ground Improvement , 6 (1), 32-41.


In Australia, increasing demand for High Speed Rail (HSR) and heavier freight transport is a technical and economic challenge for practicing engineers, designers and researchers. Because of this increased train speed and axle load, high undue stresses are transferred to the ballast and underlying formation. Ballast degradation is a major factor affecting track longevity and stability. Use of energy absorbing shock mats to reduce noise and vibrations is an established practice. The shock mat is sometimes called as Under Sleeper Pad (USP) and Under Ballast Mat (UBM) depending upon their placement position. However, studies to analyse their effectiveness in minimising ballast degradation are limited. A series of large-scale laboratory tests were conducted on ballast using a high-capacity drop-weight impact testing equipment to understand the performance of energy absorbing shock mats in the attenuation of impact loads and subsequent mitigation of ballast degradation. A numerical model was developed based on the modifed stress-dilatancy approach to capture particle breakage during impact loading. Model predictions are compared with laboratory results. This paper presents state-of-the-art review of laboratory studies and numerical modelling illustrating benefits of USPs and UBMs in the practice.