Support Condition and Traffic Loading Patterns Influencing Laboratory Determination of Under Ballast Mat Bedding Modulus and Insertion Loss

In recent years, noise and vibration concerns have grown as environmental regulations and requirements impose greater responsibilities on infrastructure owners. Under ballast mats, rubber elastomers inserted below the ballast or concrete slab, have been widely deployed and studied in Europe, but the amount of research to date in North America is limited. Current testing practices for obtaining component level properties of under ballast mats are based on European practices and loading environments. Moreover, these procedures use experimental setups, which are often not representative of field loading conditions. With this in mind, the research presented in this paper investigates static bedding modulus properties of three under ballast mats by varying support and loading conditions to simulate revenue-service field scenarios involving both ballasted and concrete slab track. Performance prediction indicators such as insertion loss (related to vibration reduction) were also evaluated using prediction models that required the use of the experimentally obtained bedding modulus results as inputs. Results showed a difference of up to 33% in bedding modulus results among the support conditions tested. Additionally, the insertion loss was changed by up to 1.8 dB. Traffic pattern simulations also demonstrated a sharp rate of stiffening due to static preload conditioning as well as a gradual rate of asymptotic stiffening with accumulated loading cycles. This finding further identifies the need to quantify a revenue service “working range” stiffness for the component.