INVESTIGATION OF MACH CONE DEVELOPMENT IN BALLASTLESS RAILWAY TRACK STRUCTURES OVER SOFT CLAYS

Abstract

High speed trains (HST) have many challenges from a geodynamic perspective; such as the case of HST operating in areas with soft soils like soft clays in Delta areas. The speeding trains can easily reach critical velocity due to the resonance of Rayleigh surface waves developed by the train and the low shear wave velocity of the soft soil. When this resonance happens it can develop a phenomenon called “Mach cones” which is similar to the ones the air jets produce at the speed of sound. This phenomenon can be observed in theoretical analytical measurements as well as in practical measurements. This paper studies the occurrence of mach cones in the soft clay soil under ballastless track structure systems and compares this phenomenon with the traditional ballasted track. Results of the displacement contours in the clay layer of the ballasted track show concentric pattern with train velocity of 250 km/h which indicated mach cone development around this velocity. Other ballastless track types modeled show that the displacement contours are distributed with no concentric pattern and indicating no mach cones even with velocities reaching 250 km/h.