Field experimental study on the dynamic response of CRTS-I ballastless track subgrade of the Shanghai-Nanjing intercity high-speed railway during operation period

Shanghai-Nanjing intercity high-speed railway, the busiest high-speed rail in China, built with the highest standards, the longest mileages, and the fastest speed among the world. Having been in operation for 5 years, it is important to figure out the performance and rules of dynamic characteristics evolution of the substructure. To study the vibration characteristics of the ballastless track subgrade after a few years of operation, in-situ train-induced tests were carried out in Shanghai-Nanjing intercity railway representative subgrade sections. The value of vertical vibration acceleration, displacement and velocity of different measuring points in both end and center of track slab under the train load is acquired, and distribution regularities of dynamic response for ballastless track subgrade on the period of operation are summarized. The results show that: At the end of track slab, the vibration acceleration value in each layer of the ballastless track subgrade structure decays dramatically in the vertical direction, which appears an exponential trend; while in the center, the vibration acceleration value decays gently in vertical direction, which appears a roughly linear trend. On the position of subgrade surface and road shoulder, vibration acceleration values are closer in both end and center of track slab; The special parts of the end of track slab mainly have an amplification effect on vibration response of the track slab and concrete roadbed, and the train's speed is considered to have the most notable amplification effect on the vibration acceleration of the end of track slab. The vibration displacements of the track slab and the concrete roadbed show a linear relationship with the variation of the train's velocity, while this trend is not remarkable on the position of subgrade surface and road shoulder, which is in accordance with the dynamic displacement distribution measured among inner part of the subgrade of high speed railways such as Beijing-Tianjin, Wuhan-Guangzhou, Zhengzhou-Xi'an.