Laboratory Research And Theoretical Analysis On The Mechanical Properties Of Cracked Rock Subjected To Complex Hydrochemistry Environment

Rock mass deformation failure and its mechanical characteristics in a chemical environment are basic'research subjects in the current environmental-geotechnical engineering research field.Microcracks,crevices,and flaws of different orders are inevitably scattered inside rock masses.However,studies on the degradation of mechanical properties and the mechanisms of deformation and fracture under complex chemical environments are still in the initial research stage.This is especially true of studies of fractured rock enduring chemical corrosion(CC)combined with freeze-thaw(FT)and dry-wet(DMW)cycles,which are rare in previous literature.Further experimental research in these researches is required.In the present workt,three test schemes were designed to conform to actual rock environments:long-term immersion in a ch:emical solution,CC during FT cycles,and CC during DW cycles.These were coupled with a theoretical analysis of the mechanical properties of fractured rock sampled from the hydrofluctuation belt of a typical bank slope,In the first test scheme,I studied the physical and mechanical properties of rock after CC in the chemical environment.Deformation properties at various stages of stress-strain curves were analyzed,along with strength parameters of the rock affected by different chemical solutions.Variations in the various stages of the deformation and failure processes of rock immersed in different chemical solutions were also observed.A nondestructive testing method was used to determine the porosity of the rock,measured indirectly through its P-wave velocities.I devised a method to calculate a chemical damage variable based on changes in porosity,and then quantitively analyzed chemical damage to the mesostructure of the rock.After the interaction between the water-chemical solution and the rock,the mechanism of the chemical damage and deterioration of the rock was further revealed from the perspective of progressive failure characteristics and energy mechanisms,These characteristics included the deteriorating law and the effects of time,energy accumulation,and energy dissipation and conversion in the strain energy of the rock immersed in natural and chemical solutions under load.In addition,the connection between energy characteristics and the chemical damage to the rock was analyzedThe effects of the stress and chemicals on the mechanical properties of the rock were considered synthetically.Chemical and mechanical damage was achieved,and total damage caused by both stress and chemicals was determined to increase the range of the damage.Thinking about the heterogeneity and complex stress conditions of the rock,the chemical damage constitutive model of the rock was established under uniaxial and different confining pressures.The damage degradation of the mesostructure of the rock and the mechanical properties of the rock were analyzed quantitatively through the damage variable and chemical damage constitutive modelIn the second test scheme,a rapid FT cycle was adopted to explore the damage deterioration mechanism and the physical and mechanical properties of the rock under the coupled effect of different water-chemical solutions and FT cycles.Variations in the physical and mechanical properties of the rock immersed in different chemical solutions after they underwent different instances of FT cycles were analyzed.Rock samples were taken from the hydrofluctuation belt of a typical bank slope in the Three Gorges Reservoir region and the construction site of the Longtan Reservoir in the Tongchuan New District,China.I analyzed variations in the physical and mechanical characteristics of rock subjected to different chemical solutions for 30 d,and then analyzed the combined effects of different CC and FT cycles.Physical properties,fracture toughness KIC,and the mechanical properties of the mode I fractured rock were studied under the coupled effect of different water-chemical solutions and FT cyclesThe damage deterioration mechanisms of chemical corrosion and FT of rock were analyzed and studied from micro view angle using a stereomicroscope,a scanning electron microscope,and an energy dispersive spectrometer.Change in the rock's porosity was used to calculate chemical damage,and a quantitative analysis method of chemical and FT cycles damage of the rock mesostructure is describedIn the third test scheme,to mimic the actual environment of the hydrofluctuation belt of a typical bank slope,I used prefabricated,fractured rock-like materials to simulate a jointed rock mass.A test scheme of DW cycles was adopted to explore the mechanical behaviors and failure characteristics of the fractured rock The variation of those factors with different DW cycle times and different chemical soaking solutions was analyzed.Also we analyzed variations in the mechanical characteristics of differently fractured dip rock under DW cycles in different chemical solutions.Crack initiation propagation and coalescence of fractured specimens were observed in real time using high-definition cameras during loading.A variable rule of crack propagation,the manner of breakthrough,and failure properties under the different crack angles were analyzed and summarizedBased on the degradation of the elastic modulus of rock under natural and DW cycles,the damage variable D was set up.An evolution equation of chemical damage of fractured specimens was devised under DW cycles.The effects of the fracture dip on the DW damage degradation were also considered.To unify the damage evolution equation of the DW test for both complete and fractured specimens,I established a general type of damage evolution equation of fractured rock undergoing DW cycles and the relations between different deformation characteristics and damage characteristics of different fractured dip rock under different chemical solutions.In addition,its damage mechanism was analyzed.These provided a test basis for establishing the evolution equations and constitutive models for fractured specimens under the combined effects of CC and DW cyclesFinally,the degradation mechanism was studied for fractured specimens undergoing CC,stress conditions,and chemical damage under load.Meanwhile,the stress fields of single fractured specimens were calculated by an ANSYS computer software application.The first,second,and third principal stress fields in the early stage of compression were obtained,and variations in the failure mechanism,crack initiation,and propagation paths of the fractured specimens were analyzed.For those single fractured specimens,the failure and damage deterioration mechanisms accompanying CC and DW cycles are discussed.Meanwhile,a damage evolution equation of the fractured specimens was set up under the combined effects of CC and DW cycles.This damage constitutive model was used to analyze the damage degradation of fractured specimens under the combined effects of CC and DW cycles.In addition,the chemical damage evolution rule was analyzed under DW cycles.The theoretical model was verified reasonably by the results of numerical analysis.