Fatigue life prediction of limestone is the basis of long-term stability analysis of surrounding rock in karst tunnel under train cycle loading. Through the low cycle fatigue tests of karst limestone under different upper limit stress, stress amplitude, loading frequency and saturated condition, the basic fatigue characteristics of the limestone are experimented. The fatigue test results show that the fatigue life of rock will be significantly reduced after saturation and increases linearly with the decrease of upper limit stress. There is also a fatigue threshold for the limestone and the fatigue threshold value increases with the loading rate increasing. The stress amplitude plays a key role in the fatigue life of the limestone. The fatigue life of the limestone increases with the loading frequency increasing. The linear relationship between the fatigue life and loading frequency satisfies the double logarithmic coordinate. By introducing a correction coefficient, a fatigue life evaluation model based on load frequency and stress level is established.
With the development of high-speed and heavy haul railways, effect of low-cycle fatigue damage of rock wall between karst cave and tunnel caused by the combined action of long-term train vibration cyclic load and the seismic dynamic loading is an important problem which restricts the long-term stability of such tunnels.
The fatigue damage law and fatigue life of limestone are the foundation of long-term stability analysis of surrounding rock of karst tunnel under the train vibration cyclic load and the seismic dynamic loading. However, in the previous research, the fatigue properties and prediction models of metal and concrete materials have been studied a lot, but the fatigue properties of rocks were seldom studied. Burdine (1963) found that the fatigue failure of Berea sandstone occurred within a certain number of cycles when the specimen reached a certain upper limit stress. Haimson & Kim (1972) proved that the fatigue life of the two marbles is closely related to the rock type and stress level. When the stress level is different, the fatigue failure cycles of Georgia marble and Tennessee marble are different. Attewell & Farmer (1973) studied the effect of loading frequency (0.3Hz, 2.5Hz, 10Hz, 20Hz) dolomite fatigue life. Ishizuka & Abe (1990) also proved that the fatigue life of rocks increases with the increase of loading frequency, and the fatigue strength of rocks under wet conditions is about 7% lower than that under dry conditions. Singh (1989) proved that the fatigue life of Australian miscellaneous sandstone increases with the decrease of stress amplitude, and the number of loading cycles increases logarithmically with the decrease of stress amplitude. Zhen & Hai (1990) show that the deformation caused by sinusoidal wave loading is greater than that of triangular wave, and the longer the cyclic amplitude, the shorter the life of rock. Ge & Jiang (2003) found that the rock fatigue failure has a threshold value, threshold value corresponds to demarcation point of the linear and nonlinear.
