The subgrade defect of expansive soil is of main concern in high-speed railway construction. Based on the monitored data of the cutting subgrade of Yun-Gui high-speed railway and using software FLAC3D

a three-dimensional dynamic analysis is performed to study the dynamic behavior of the cutting subgrade under the moving train load. It is shown that the dynamic response can be described by numerical model and the predicted variation is consistent with the observations. The vertical dynamic stress of subgrade is exponentially attenuated and the variation of vertical dynamic displacement with depth follows a power law. The dynamic displacement value of railway surface is 0.95 mm which satisfies the requirement of high-speed railway specification. The effect of working conditions on dynamic responses of subgrade is significant. The dynamic stress and vibration velocity of subgrade surface increase due to immersion condition. Laying waterproof and drainage structure layer will improve dynamic stress distribution

reduce dynamic displacement of railway surface and enhance anti-vibration performance of subgrade. The conclusions can provide references for engineering practice and theoretical research of high-speed railway in expansive soil area.