Abstract: In view of the long-term dynamic stability and replacement thickness of red clay cutting bed under ballastless track of Wuhan-Guangzhou high-speed railway, the variation rules of dynamic strain of red clay in original structure under cyclic loading with vibration times are studied by means of the modified stress-controlled dynamic triaxial test instrument, and values of the critical dynamic stress of red clay in original structure are obtained under 11 kinds of test conditions. According to the trend features of curves, the
curves can be divided into three types: attenuated, critical and destructive ones, and they are the same as those of other cohesive soils. Based on the results of laboratory and field tests, the long-term dynamic stability of red clay cutting bed under ballastless track of Wuhan-Guangzhou high-speed railway is preliminarily evaluated by use of the critical dynamic stress method, and the corresponding minimum replacement thickness is given. Influences of water content ratio, confining pressure and consolidation ratio on the critical dynamic stress of red clay and the replacement thickness of cutting bed are discussed. Two practical empirical formulas are obtained by means of multiple linear regressions. The critical dynamic stress decreases linearly with the increase of water content ratio, and increases linearly with the increase of confining pressure and consolidation ratio. The replacement thickness increases linearly with the increase of water content ratio and decreases linearly with the increase of confining pressure, and the influences of consolidation ratio are not obvious on it. A new idea is put forward for the long-term dynamic stability evaluation and the determination of cutting bed replacement thickness under ballastless track of high-speed railways, and the first-hand valuable data are accumulated for further studies on dynamic characteristics of red clay.