Study On Shear Creep Characteristics Of Weak Intercalation Under Acid Corrosion

The weak interlayer(Permian carbonaceous shale)in the slope of an open pit mine has low mechanical strength and obvious creep effect.When affected by the acidic hydrogeological environment of the mining area for a long time,its mechanical properties will gradually deteriorate,and the creep characteristics will significantly change,causing a very adverse impact on the long-term stability of the mine.Therefore,it is of great significance to study the shear creep characteristics of weak intercalated layers under acid corrosion,which can lay a solid foundation for long-term stability analysis of high slopes in mines with weak intercalated layers.In this paper,the weak intercalation in Mount Huangshan limestone mine is taken as the research object,and the direct shear test,shear creep test and electron microscope scanning test of weak intercalation under different acid etching conditions are carried out by using indoor test,theoretical analysis and other methods,Based on the test results,a shear creep damage constitutive model for weak intercalations subjected to acid etching was established.The main research conclusions are as follows:(1)Acid etching has a significant deterioration effect on the shear strength parameters of weak intercalation.The average shear strength,internal friction angle,and cohesion of the weak intercalation gradually decrease with the increase of the acidity of the immersion solution and the increase of the acid etching time.After acid etching,the compression stage and unstable fracture development stage of the shear stress displacement curve of the weak interlayer become more obvious,the elastic stage is shortened,and the stage after failure presents a "downward convex" decline.(2)Acid etching has a significant impact on the creep characteristics of weak intercalations.As the acidity of the acid etching solution increases,the shear stress required for the weak interlayer to enter the accelerated creep stage gradually decreases,the total creep duration gradually decreases,and the total creep displacement gradually increases;Under the same shear load,the instantaneous displacement and steady-state creep displacement of the weak interlayer gradually increase with the enhancement of the acidity of the acid etching solution.Under the same acidic condition,with the increase of shear load,the instantaneous displacement of the weak interlayer gradually decreases,while the steadystate creep displacement gradually increases;The accelerated creep rate of the weak intercalation increases with the increasing acidity of the acid etching solution;When a weak interlayer corroded by a strong acidic solution fractures,the shear surface fluctuates greatly,the strike is unclear,and the overall sample is relatively broken.The failure of the sample gradually changes from brittle failure to plastic failure.(3)The degradation mechanism of acid etching on the mechanical properties of weak intercalated layers lies in the following: the chemical reaction of the mineral components inside the weak intercalated layers occurs in an acidic environment,resulting in an increase in internal pores and fissures,changes in the bonding mode between mineral particles,weakening of the bonding strength,and changes in the internal micro and micro structures,leading to the gradual deterioration of the mechanical properties of the weak intercalated layers.(4)Taking chemical damage and stress damage into account and introducing them into the nonlinear composite element model,a nonlinear creep damage constitutive model for weak intercalated layers under acid corrosion was obtained.After parameter identification,it was found that the model fitted well with the shear creep test results,verifying the rationality of the model.