Investigation of long-term behavioral models of salt cavern under cyclic loading

Natural gas, air and oil materials can be stored in caverns, which are created in salt domes and have thick rock salt layers. These caverns may be subject to cyclic loading on a daily, weekly, and monthly basis due to the internal consumption of accumulated materials. The amount of deformation created over long periods of time effects the stability of the cavern. A number of models have been proposed to predict the long-term deformation of rock salt. One of these models is the Lubby2 model. In this research, the long-term behavior and stability of salt cavern storage under cyclic loading has been investigated. As a case study, the geometry of the German Hantorf salt cavern compressed air has been used. Salt rock properties of the Nasrabad Dome were considered. Creep tests were conducted on samples of rock salt at three stress levels in a stepwise manner and each test in different temperatures. Parameters of the Lubby2 model were determined. In order to investigate the effect of loading and unloading frequency on rock salt behavior, cyclic loading tests with different frequencies were also performed. For the purposes of this research, LOCAS finite element software with the Lubby2 model was utilized. A geometrical model of the cavern was built and executed in the software. The long term stability of the cavern and ground settlement were also investigated. tThe results showed that the Maxwell's viscoelastic coefficient in Lubby2 model is dependent on cycle loading frequency and it decreases exponentially with increasing loading frequency. Maxwell's viscosity coefficient decreases with increasing loading frequency. The deformation of cavern and ground subsidence with daily loading frequency has a rate of 10% and 8.6% higher than a cavern with constant loading, respectively. The effect of the cyclic load on Maxwell's viscoelastic coefficient was seen and the Lubby2 model was corrected for cyclic loading.