Abstract
Solution mining for glauberite salt rock is a long-term process that takes several years to several decades. Therefore, deposit deformations and subsidence of ground surfaces are time-dependent deformation problems that should consider the effect of water dissolution. In order to investigate the time-dependent deformation characteristics of glauberite salt rock, tri-axial time-dependent deformation tests were conducted under the condition of 4 MPa confining pressure and 5 MPa axial pressure with infiltration pressures of 3, 2, 1, and 0 MPa, respectively, and the micro-CT scan system was used to scan the glauberite specimens before and after the experiment in order to study the fracture evolution inside the specimen, and a damage constitutive model was established to fit the time-dependent deformation curves based on the damage mechanics and effective stress principle. To simulate the solution mining process, the time-dependent deformation process of glauberite salt rock was divided into three stages: hydraulic connection stage, water-saturated stage, and drainage stage. The results demonstrate that the hydraulic connection time for glauberite salt rock decreases with increasing infiltration pressure. The time-dependent deformations of the specimens at the hydraulic connection and saturated-water stages are significantly affected by the effective stress and continual mineral dissolution. At the drainage stage, the softening degree of the solid skeleton mechanical properties, which is caused by the dissolution effect and infiltration pressure loading history, decides the deformation of glauberite salt rock. In addition, the degree of softening inside glauberite salt rock caused by dissolution becomes more severe with increasing infiltration pressure using the micro-CT scan technology. Lastly, the time-dependent damage constitutive model is able to describe the tri-axial time-dependent deformation behavior of glauberite salt rock, and the variations of time-dependent deformation parameters further indicate the damage evolution of the solid skeleton mechanical properties of glauberite caused by infiltration pressure and dissolution effect.
Highlights
Glauberite is an unusual salt rock that mainly consists of sodium sulfate and calcium sulfate, i.e., Na2 Ca(SO4 )2, in an anhydrous state [1]
Comparing the time-dependent deformations of specimens 1, 2, and 3 with that of specimen 0, it is obvious that infiltration pressure causes degradation of mechanical properties of the glauberite specimen
At the hydraulic connection stage and water-saturated stage, the time-dependent deformations of the specimens were dominated by the effective stress and the degree of weakening of the solid skeleton caused by the dissolution effect
Summary
Glauberite is an unusual salt rock that mainly consists of sodium sulfate and calcium sulfate, i.e., Na2 Ca(SO4 ) (anhydrous sodium calcium sulfate), in an anhydrous state [1]. An important raw material in the chemical industry, can be extracted from glauberite deposits using. Energies 2020, 13, 1797 solution mining technologies [3]. Solution mining is a long process of ore body dissolution that takes several years to decades. Based on the principle of effective stress, subtracting the total stress to pore water pressure gives the effective stress. During this process, ore bodies are subjected to mineral dissolution and dynamic effective stress changes, and time-dependent behaviors of ore bodies occur with the gradual evolution of the pore structure
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