5. Conclusions
In this study, we performed cyclic loading tests on rock salt samples to determine the fatigue life of the samples under different upper and lower stresses, speeds of cyclic loading, temperatures, and confining pressures. We found that as the upper loading stress increased, the fatigue life decreased con- siderably. Based on quantitative analysis, we obtained the S–N curve with a fitting coefficient of 0.9995, which shows that the fatigue property of salt rock is similar to that of metal materials.
When the upper stress dropped to 75% of the compression strength, the fatigue life of salt rock was more than 5000; hence we suggest that the fatigue limit of salt rock is equal to 75% of the compression strength. When the lower stress increased to
50% of the compression stress, the fatigue life showed a notable increase. The above results can be useful for determining the pressure limits of gas injection and production of salt rock gas storage.
We also found that as the cyclic loading speed rises, the fatigue damage pattern changes; the percentage of the decelerating and uniform damage phases decreases and that of the accelerating damage phase increases as the cyclic loading speed drops. These results can be useful for determining the limits on the rate of gas injection and the production of salt rock gas storage.
The fatigue life increases notably as the temperature increases. The fatigue life also increases with higher confining pressures; this has implications on the safety of salt rock gas storage located at different depths.
5. ConclusionsIn this study, we performed cyclic loading tests on rock salt samples to determine the fatigue life of the samples under different upper and lower stresses, speeds of cyclic loading, temperatures, and confining pressures. We found that as the upper loading stress increased, the fatigue life decreased con- siderably. Based on quantitative analysis, we obtained the S–N curve with a fitting coefficient of 0.9995, which shows that the fatigue property of salt rock is similar to that of metal materials. When the upper stress dropped to 75% of the compression strength, the fatigue life of salt rock was more than 5000; hence we suggest that the fatigue limit of salt rock is equal to 75% of the compression strength. When the lower stress increased to50% of the compression stress, the fatigue life showed a notable increase. The above results can be useful for determining the pressure limits of gas injection and production of salt rock gas storage.We also found that as the cyclic loading speed rises, the fatigue damage pattern changes; the percentage of the decelerating and uniform damage phases decreases and that of the accelerating damage phase increases as the cyclic loading speed drops. These results can be useful for determining the limits on the rate of gas injection and the production of salt rock gas storage.The fatigue life increases notably as the temperature increases. The fatigue life also increases with higher confining pressures; this has implications on the safety of salt rock gas storage located at different depths.
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