Study On Field Measurement And Full-scale Model Test On Dynamic Response Of High-speed Railway Subgrade

The rapid development of China high-speed railway has brought great convenience and economic benefits for national development and people’s daily live. As an important foundation under the slab track, subgrade provides adequate support and stiffness for the upper structure to meet the security and comfort requirement. Therefore, the dynamic response of the high-speed railway subgrade is an important indicator of the service performance, comfort and safety evaluation.Bridges are being widely used in many of China high-speed rail lines across the special topography. A field measurement of viaduct was carried out at Jiaxing high-speed railway station to collect the measured data of vibration transfer law among viaduct bridge span structures, piers, foundation and the ground around. The result shows that the load-transfer behavior of the box-girder structure is not completely symmetrical and affected by the factors as structure type, material properties, etc. The cushioning effect of isolation bearing significantly reduces the vibration strength which transmits from the deck to the pier. The pipe-pile foundation causes the stiffness mutation of the connection part between the pier and cap, and a rapid increase of the vibration strength of the pier bottom.Culvert-subgrade transition sections are widely used in high-speed railways. The difference of stiffness and strength between culvert and subgrade may cause uneven settlement. A field measurement of culvert was carried out at Liyang high-speed railway station in order to research the vibration response of culvert-subgrade transition section and the influence of the culvert structure on vibration. The result shows that the characteristics of the culvert affect the vibration damping effect obviously and the vibration at the top of the culvert enhances.Subgrade is the most commonly used foundation structure under the track. The dynamic response of the subgrade is an important indicator of the strength of the vibration performance. The field measurement in this paper shows that the train load in the low speed condition can be regarded as quasi-static moving load, and courses lower vibration in the foundation and ground. The strength and the frequency of the vibration increase when the train speed increases. The vibration will become very strong when the rain reaches the critical speed. Because of the limitations of the field test, such as complex field conditions and internal dynamic which cannot be fully measured, a full scale physical model test was used to measure the moving effect, cyclical effect of the vibration performances in different speed and conditions by Zhejiang University with a self-developed distributed loading system. Experimental studies were taken on vibration response of the track-subgrade system and distribution characteristics, and attenuation law of the internal stress of the subgrade. By studying the correlation of the dynamic stress and speed, the empirical formula of dynamic stress amplification factor was proposed. The empirical formula of dynamic stress in ballastless-track subgrade was proposed based on the attenuation law of the subgrade surface stress and the internal dynamic stress.