Influence of loading history on creep behavior of rock salt

Creep is a vital factor that affects the long-term stability of gas storage salt caverns. When we conduct a labo-ratory creep test of rock salt, compared with the single-stage loading method, the multi-stage loading method is used more frequently as it eliminates the discreteness of the sample. However, the early loading history affects the later creep behavior when the multi-stage loading method is used. To study the influence of loading history on the creep behavior of rock salt, the multi-stage loading triaxial creep test of rock salt and synchronous acoustic emission test were performed. Then, the numerical sample is established based on the laboratory test results and the discrete element numerical simulation is carried out. Single-stage loading and multi-stage loading creep tests were carried out on the initial numerical samples, respectively. Finally, the multi-stage loading data processing methods were compared using numerical simulation data. The results indicate that: (1) the improved multi-stage loading data processing method works well and it is recommended to use this method to process the multi-stage loading creep data. (2) Cracks are more developed in multi-stage loading sample, which experienced an early loading history, than in samples under single-stage loading. The damage accumulation in rock salt leads to its mechanical properties deterioration, which makes the creep deformation more prone to occur in the later stage. (3) The steady-state creep rate of rock salt is independent of loading history, only related to stress and tem-perature. The effect of damage accumulation in the loading history is mainly reflected in the transient strain and the strain in the transient creep phase. The study is helpful to further understanding the influence of loading history of rock salt on its creep, and provides an important basis for the design, construction, and operation of gas storage salt caverns.