| Glauber's salt is a typical soluble rock salt with good rock quality,difficult weathering,moderate hardness,and high strength.It consists of sodium sulfate which is easily soluble in water and calcium sulfate which is slightly soluble in water.Its ore body is an important sources of chemical raw materials have high industrial value.At present,it is generally exploited by water-soluble mining methods.However,due to the shortcomings of low resource utilization,high labor intensity,low work efficiency and environmental pollution,some well-known scholars put forward the method of in-situ leaching mining for their deposits after continuous research.However,in this mining process,the ore body is under the action of leaching and in-situ stress for a long time.With the continuous change of the leaching conditions(concentration and temperature of the leaching solution),fine cracks are generated inside the ore body,and the mechanical properties are weakened.As a result,the cavity is destabilized,and the cavity after the instability is gradually lost to support the overburden.Under the action of gravity,the overburden deformed downward and deformed to cause the ground to sink.Obviously this is a time-dependent creep problem under different leaching conditions,and the research on this problem can be calcium on the one hand.The leaching and mining of the Glauber's salt mine and the water-soluble mining of the salt-bearing salt-bearing salt rock provide certain theoretical guidance.On the other hand,it has certain engineering significance for the stability analysis and surface subsidence of salt rock cavern construction.Therefore,in order to study the creep properties of glauberite salt under different leaching conditions,this paper combines theoretical analysis with experimental research to carry out axial compression of 5MPa,confining pressure of 4 MPa,and different osmotic pressures(3,2,1MPa),different permeate concentrations(fresh water,semi-saturated sodium chloride solution,saturated sodium chloride solution),different temperature(30 ° C,60 ° C,90 ° C)conditions of glauberite triaxial compression creep test,will be The creep test of the test pieces is divided into four processes: immersion-connected creep,saturated creep,drainage creep and axial pressure 20 MPa creep.The creep characteristics of the glauberite in different creep processes are compared and analyzed.Before and after the test,the glauberite samples were scanned by CT and the crack propagation law was observed.Finally,the generalized Kelvin model is improved based on the nonlinear rheological mechanics theory,and the creep constitutive model of the glauberite is constructed according to the experimental conditions.The creep test data is used to fit the model.The effect was fitted to verify the applicability of the improved model under the conditions of this test.Thus the following conclusions are obtained:(1)It is found that the main factors determining the dissolution and connectivity of glauberite specimens are the concentration of solution and osmotic pressure in the process of creep.When the osmotic solution is fresh water,only osmotic pressure greater than 1MPa can dissolve.When the osmotic solution is semi-saturated sodium chloride solution,only osmotic pressure greater than 2MPa can dissolve.When the osmotic solution is saturated sodium chloride solution,only osmotic pressure greater than 3MPa can dissolve.When glauberite can be dissolved,the main effect on creep deformation is the softening effect of sodium chloride solution on the bottom of specimens under the action of time.When glauberite cannot be dissolved,the main effect on creep deformation is the erosion of impurities in the glauberite and calcium sulfate.(2)During the saturated water creep process,the creep strain increases with the increase of temperature,but the increase is gradually reduced,and thermal expansion occurs.Under the conditions of temperature of 30°C,60°C,90°C and osmotic pressure of 3MPa,the creep strain after creeping for 72 h in fresh water is 0.001%,0.003%,0.007%,and the permeate is half.The creep strain of the saturated sodium chloride solution was 0.0015%,0.002%,and 0.0035%,respectively.The main factors affecting the creep deformation of this process are the permeate concentration and the effective stress.(3)During the process of drainage creep,the creep strain and its increase increase with the increase of temperature.Under the conditions of temperature 30°C,60°C,90°C and osmotic pressure 3MPa,the permeate is fresh water.After 72 h creep,the creep strains were 0.0995%,0.1515%,and 0.254%,respectively.When the permeate is a semi-saturated sodium chloride solution,the creep strains were 0.0715%,0.1035%,and 0.173%,respectively.The main factors affecting the creep deformation of this process are the degree of weakening of the mechanical properties of the solid structure of the glauberite by the temperature and the history of the leaching process in the first two processes.(4)During the creep process of axial pressure increase to 20 MPa,the creep strain increases with the increase of temperature,but the increase range decreases with the increase of temperature.Under the experimental conditions of this paper,various factors are related to calcium.The influence of creep deformation of Glauber's salt is from large to small: concentration > osmotic pressure > temperature,and increasing the concentration of permeate can weaken the effect of temperature on the creep deformation of glauberite.The permeate fluid changed from fresh water to semi-saturated sodium chloride solution.The creep deformation of the glauberite was reduced by 0.4035%,and the average conversion from the semi-saturated sodium chloride solution to the saturated sodium chloride solution was reduced by 0.066%.(5)The creep strain of the glauberite creep test under different temperature and concentration leaching increases with the increase of temperature and osmotic pressure,decreases with the increase of concentration,and when the test piece can be dissolved,the effect of temperature on creep deformation of glauberite is non-linear.When the test piece cannot be dissolved,the effect of temperature on the creep deformation of glauberite is almost linear.(6)The number of cracks on the surface of the Glauber's salt sample under different temperature and concentration leaching increases with the increase of osmotic pressure,and decreases with the increase of the permeate concentration.The opening and breadth of the crack increase with temperature.(7)The dissolution zone of glauberite dissolved under different temperature and concentration leaching gradually increased with the increase of temperature,and the opening and length of the fracture of the cross-section pore increased with the increase of osmotic pressure.The change of pore fracture rate increases with the increase of temperature and osmotic pressure,and the creep strain of glauberite increases with the increase of the fracture rate of the framework pore.The dissolved and infiltrated area of the specimen section and the number of cracks gradually decrease with the increase of the scanning height.Under the same stress condition,the creep deformation gradually decreases with the increase of the height of the limestone specimen.(8)Based on the nonlinear rheological mechanics theory,the generalized Kelvin model is improved.According to the creep test data,the generalized Kelvin model before and after the improvement is fitted,and the improved generalized Kelvin model is found under different temperatures and concentrations.The glauberite creep test has a higher fitness fit. |
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