Basic Research On Ore Body Deformation And Surface Subsidence Prediction In Glauberite In-Situ Solution Mining

Salt deposit is the basic materials to the chemical industry. The drilling solution method is widely used for the mining of salt ore owing to their diffluent characteristics. This method also applies to the mining of glauberite. However, when the soluble component had been dissolved, the residual solid frame also have the supporting capacity which will not only affect the seepage and transport properties of the fluid, but also have deeply effect to the surface subsidence and the deformation of the salt ore and overburden strata. The deformation characteristics have been closely related to the meso-structure evolution and mechanical properties weaken during the mining process. In order to reveal the inherent characteristics and perform the corresponding theoretical analysis of the subsidence prediction, the paper conducted some experimental studies on the structure evolution and mechanical properties under the different solution condition during the process of the glauberite in-situ solution mining, furthermore, based on the experimental results, the theoretical and numerical simulation were adopted to analysis the deformation of ore body and overburden strata during the leaching process. The following conclusions were obtained:1. The CT tests of the glauberite specimens under different temperatures and dissolved time were conductedtoinvestigate the microstructural evolution law by using the μCT225kVFCB high precision industrial CT testing machine. These research findings were obtained:dissolution mechanism of glauberite specimens varied with the different temperatures of the leaching solutions. The hydration swelling of argillaceous cement is obvious in the room temperature; The dissolution mainly occurred along the hydration cracks in the35℃and65℃; The temperature plays a important role in the spread of solution concentration under the95℃condition.2. Under the different solution temperatures, The initial crack location of the glauberite specimens has the following characteristics:One is the interface between the white glauberite crystal and argillaceous cement, the other is the inside of the glauberite with larger crystal grains. Furthermore, the temperature affected the expansion ratio of glauberite obviously, under the range of experimental temperature, the expansion ratio decreases with increasing temperature3. Mechanical characteristic test of the standard glauberite specimens those soaked in different concentrations solution for20d were conducted by using the electro-hydraulic servo TYT-600machine. The results of research contains:The disintegration of hydrophilic minerals in the cement, the dissolution of sulfate, the exchange of ions and the erosion damage leading to the serious weakening of mechanical properties. After soaked in saturated and sub-saturated solution for20d, The weakening ratio of extreme strength reduced to0.2and0.1, respectively.4. The triaxial compressive deformation test of standard glauberite specimens with φ50mm×100mm were conducted under the conditions with and without pore water after dissolving. The research found that the axial deformation had larger difference under the two conditions due to the weakening of the mechanical properties of the solid frame affected by the pore pressure and mineral solution.5. The Nishihara model is used to describe the triaxial deformation properties affected by the different osmotic pressure under the long-term compressive pressure, through defining the relationship that porosity changed over time, establishing the deformation constitutive equation:And fitting with the measured data, coming up with some material parameters such as shear modulus and viscosity coefficient.6. Based on the layered characteristics of glauberite deposits and the properties of porosity media caused by the dissolved glauberite, to revise the parameters of existing mining subsidence prediction formula, such as the mining height, the tangent of the main impact angle, the typical prediction formula of solution mining was obtained which were applied to the glauberite in-situ solution mining. Furthermore, based on the physical mechanical characteristics of the glauberite, compile the relevant program to simulate the surface subsidence and the deformation of the overburden rock under the different solution mining conditions.