Study On Dynamic Mechanical Properties Of Red-sandstone Under Wet-Dry Cycle In Acidic Environment

In rock engineering fields such as high and steep slopes in reservoir area,dams and surrounding rocks of underground engineering,some rock and soil mass have been in the environment of alternating wet-dry cycles for a long time due to the rise and fall of groundwater level,rainfall and fluctuation of water level in reservoir area.Compared with the conventional static loading condition,the mechanical properties and failure mechanism of rock under the coupling action of high strain rate and wet-dry cycles are essentially different under the disturbance of dynamic loads such as mechanical excavation,blasting,rock burst and earthquake.Aiming at the practical needs of the above projects,this paper takes red-sandstone as the research object,with the help of advanced testing technology(SEM),theoretical analysis and comprehensive use of experimental research,the dynamic characteristics and failure mechanism of redsandstone under the action of wet-dry cycling in acidic environment were comprehensively investigated.The research contents and main work are as follows:(1)Physical and mechanical parameters such as density,longitudinal wave velocity,water absorption,uniaxial compressive strength and tensile strength of red-sandstone under wet-dry cycling in acidic environment were tested,and the evolution law of these physical and mechanical parameters with the number of wet-dry cycles and pH was analyzed.The appearance of the specialized specimens was observed by scanning electron microscopy,and then the damage degradation mechanism of redsandstone under the action of wet-dry cycling in neutral solution and acid environment was measured and compared.(2)With the help of SHPB test system,the dynamic compression tests of redsandstone specimens under wet-dry cycling in acidic environment were carried out.The variation of stress-strain curves,elastic modulus,peak stress,energy dissipation,macroscopic failure characteristics and fractal dimension were obtained with strain rate,number of wet-dry cycles and pH.According to the slope of the linear fitting equation,the sensitivity of compressive strength,elastic modulus and energy consumption density to the above three factors was discussed.(3)The Brazilian disc loading method was used to study the dynamic tensile properties of red-sandstone after wet-dry cycling in acidic environment.The change rules of dynamic tensile strength,energy dissipation,macroscopic failure characteristics and average size of fragments with loading rate,number of wet-dry cycles and pH were analyzed.The sensitivity of dynamic tensile strength and energy consumption density to the three various influencing factors was studied.(4)Considering the effect of strain rate(loading rate)in damage variable,the decay function model of compressive strength and tensile strength of red-sandstone specimens after wet-dry cycling was established,which provides a reference for the prediction of rock dynamic strength under long-term wet-dry cycling.(5)Dynamic fracture toughness of red sandstone specimens under wet-dry cycling in acidic environment was tested by NSCB method.The effects of loading rate,number of wet-dry cycles and pH on dynamic fracture toughness were obtained.The phased expression of dynamic fracture toughness of red sandstone changing with loading rate was established,and the variation of sensitivity of fracture energy to the three influencing factors was discussed.(6)Based on the scanning electron microscopy(SEM)test of fragment morphology after dynamic compression test,the variation of fracture morphology and damage fracture modes with strain rate,number of wet-dry cycles and pH was analyzed,and the micro-mechanism of macro-damage and failure mechanism of red sandstone under wet-dry cycling in acidic environment was revealed.(7)Based on the theory of rock damage and fracture,combined with the dynamic compression test results of red-sandstone under wet-dry cycling in acidic environment,the damage evolution equation and constitutive equation of red-sandstone considering both strain rate and wet-dry cycling effect were established on the basis of Weibull distribution statistical damage model.Finally,the reliability of the model was verified by the comparison between experimental curves and theoretical curves.The research results can provide reference for rock dynamic response and related engineering design under complex environmental condition.The paper has 128 pictures,27 tables,and 192 references.