| Glauberite salt deposit is an important type of sodium sulphate deposit,and sodium sulfate is a valuable chemical raw material.The concentration of sodium sulfate brine is up to 33.62% when it is mined,and it has a very high exploitation value.Since the 1980 s,the chamber solution mining method has been applied to the production of glauberite ore.Some of the shallow buried glauberite deposits has been carried out by such method.Up to now,from all the glauberite mine,open-air heap leaching and chamber solution mining are the main mining methods.The change of the internal structure will lead to the change of the mechanical properties and permeability of the rock,which will affect the in-situ leaching efficiency when the glauberite salt rock is soaked in water.In other salt deposits such as rock salt-anhydrite-glauberite salt and so on,the glauberite salt layer is often in the form of roof,bottom plate or in the form of interlayer.Therefore,the study on the weakening effect of mechanics and the change of pore structure of glauberite salt rock under different leaching conditions are also important for the stability of salt rock cavity construction.In this paper,the macroscopic mechanical properties and the internal meso-structure of the glauberite were studied by means of experimental studyand mechanism analysis,and the mechanical properties weakening and the microstructure damage were studied.The main contents and results of this paper are as follows:(1)Experimental study on mechanical properties of natural Glauberite Salt Rock was done.The results show that the average compressive strength of glauberite salt rock in the natural state is 12.08 MPa,and the failure form is the typical columnar cleavage of brittle rock material and it belongs to soft rock classified by rock strength.The average tensile strength is 1.48 MPa,the shear strength curve is τ = 1.3 + σ tan40.6 °,the cohesion is 1.3MPa,the internal friction angle is 40.6 °,and the mechanical parameters above are offered to compare with those of mechanical tests by solution weakening.(2)Experimental study on mechanical properties of glauberite after leaching under different temperature was done.Uniaxial compressive strength test,tensile strength test and variable angle shear test of glauberite were carried out which were immersed in aqueous solution at 35 ℃,65 ℃ and 95 ℃ for 10 hours,and the mechanical properties were compared.The results show that the average compressive strength of glauberite soaked in 35℃ water for 10 hours is about 9.60 MPa and the softening coefficient is 0.79,and the failure mode is mainly monoclinic shear failure.The average tensile strength is 1.18 MPa,the linear regression equation of shear strength is τ = 0.8 + σ tan39.1 °,the cohesion is 0.8MPa,the internal friction angle is 39.1 °;The compressive strength of the glauberite samples which are soaked in 65℃ water for 10 hours is about6.92 MPa,the softening coefficient is reduced to 0.57,and the failure mode is shear failure and tensile failure,and the plastic destruction characteristic begins to appear.And the average tensile strength is 0.68 MPa.The linear regression equation of shear strength is τ = 0.7 + σ tan38.1 °,the cohesion is 0.7 MPa,the internal friction angle is 38.1 °;The compressive strength of glauberite soaked in95℃ water for 10 hours is 2.25 MPa,the softening coefficient drops sharply to0.19,and the shear failure and torsional failure are promoted at the same time.The destruction form is more complicated and the plastic deformation is obvious.The tensile strength is 0.27 MPa,the shear strength linear regression The equation τ = 0.6 + σtan37.0 °,the cohesion is 0.6 MPa,and the internal friction angle is 37.0 °.(3)Study on CT number damage distribution of glauberite under different immersion-stress conditions was done.The orthogonal experiment was carried out under the three kinds of stress(1MPa,1/2 compressive strength and peak strength)times three kinds of temperature conditions(35℃,65℃,95℃)which sumes 9 experimental conditions,and nine Φ50 × 100(mm × mm)specimens were used for the nine conditions respectively.Corresponding to nine kinds of orthogonal experimental conditions,the CT scan was carried out after axial loading,and the CT number of the scanning was statistically analyzed.The results showed that the deformation of the specimen increased with the increase of the stress value of the test sample.The increament of the density damage increases with the increase of the immersion temperature.In the same stressstate,the average density damage increases with the increament of the immersion temperature.(4)Study on the law of crack evolution of glauberite under different leaching-stress conditions.Based on the CT images of the glauberite samples under different leaching and stress conditions,the quantitative analysis of the cracks number at different scales was carried out.It was found that the variation of the cracks number in various types was related by axial loading under different temperature.The microcracks decrease while cracks and fissures increase because when the damage of glauberite caused by dissolution and stress increases,microcracks gradual expand while more and more convergence and connection occure,and the shape and the size gradually become larger.After several qualitative changes,the original microcracks co-evolved into cracks and even fissures,and many cracks can also co-evolve into fissures,so that different types of cracks show the above changes in the law.(5)Study on the change of pore structure of glauberite in different leaching-stress conditions was done.Based on the CT images of glauberite,the porosity,mean pore size and specific surface area of the specimen were analyzed statistically.Based on the same stress state,the values of the pore parameters increase with the increasement of temperature.But the initial damage degree caused by different temperature leaching is different,which leads to the different degree,type and mechanism of damage after loading,so that with the increase of stress when the specimen with large initial damage is loaded,the process offormation and expansion of pore fissure is more intense with the greater the degree of damage at the end. |
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