A theoretical method for the investigation of the effects of soil improvement on train induced ground-borne vibrations

Ground-borne vibrations by railway trains are generated at the rail-wheel interface due to the passage of wheels and due to irregularities of wheels and tracks. These vibrations need to be predicted and controlled during the design and service of the railway for the safety and the serviceability of the railway to avoid possible vibration induced problems such as settlement and differential settlement due to their compaction effect, liquefaction and discomfort of people. While such railway vibrations are modeled by different techniques, only few studies do exist to analyze them in the case of soil improved conditions. In this study we propose a mathematical framework to study the effects of soil improvement on the ground-borne vibrations induced by the railway trains. We use an experimentally calibrated model which utilizes the evolutionary random process approach in order to model the time varying transfer functions between the axles of the train and fixed observation point. The railway is modeled as a Winkler foundation with rail pads and corresponding transfer functions are used. The target area of this study is the Eminönü-Alibeyköy Tramway Line in ˙Istanbul, which is under construction and planned to be completed in late 2018. Due to poor soil conditions at the specific stations along the proposed tramway route, soil improvement by the application of geosynthetics are performed at the site and taken into account in our model. The improvement in soil conditions are modeled as increased vertical soil stiffness in the Winkler foundation of the evolutionary random process model. To model the various tramway loading conditions, both the 5-axle and 6-axle tramway configurations with non-uniform axle spacing are considered. We show that by increasing the vertical soil stiffness ksb, the vibration velocity and acceleration levels can be reduced significantly. By implementing model proposed, we present the reduction of the vibration velocity and acceleration levels as the functions of soil improvement parameters and discuss our findings and the applicability of the model.