| Since the "13th Five-Year Plan",the pace of infrastructure construction in China has been further accelerated,in the construction of projects in key areas,many cold area projects have been built,during the construction of these cold area projects,more and more complex rock engineering problems have appeared,most of the construction problems of projects in cold areas are related to rock freezing damage.At the same time,with the further development of China’s modern industry,the consumption of fossil fuels such as coal,oil and natural gas increases,and the amount of pollutants emitted from the atmosphere rises sharply,resulting in the deterioration of environmental pollution.Following global warming,acid rain has become a global environmental problem that has attracted much attention.With the proposal of the key projects of the "14th Five-Year Plan",such as the Sichuan Tibet railway and the railway along the border,in order to ensure the engineering safety in the cold region,the research on the stability of rock and soil structure,the strength,deformation and failure characteristics of rock materials and other mechanical properties has inevitably become the primary problem faced by the construction of key projects.Therefore,it is of great practical significance to study the deterioration law and damage mechanism of rock mechanical properties under the coupling action of acid solution erosion and freeze-thaw cycle.Aiming at the problem of freezing and thawing of rock in rock mass engineering in cold regions,the paper selects sandstone as the sample,through indoor freezing and thawing cycle test,acid corrosion test,scanning electron microscope observation and triaxial compression test,the quality change rate,density change rate,longitudinal and transverse wave velocity change rate,microstructure and mechanical properties of sandstone were analyzed.Then,based on the Lemaitre strain equivalent hypothesis theory,the deterioration degree and damage evolution law of rock materials were described by introducing the damage variables that can reflect the failure process of rock,the total damage variables of rock under the coupling action of multiple factors were deduced,and the damage evolution equation and constitutive model of rock under the coupling action of multiple factors were established by using the theory of continuous damage mechanics.The main research work and achievements of this paper were summarized as follows:(1)The quality,density,longitudinal and transverse wave velocity and triaxial compressive strength of acid corroded sandstone were analyzed,and the microstructure and failure mechanism of sandstone specimens were observed and analyzed by scanning electron microscope(SEM).The sandstone soaked in acid solution had undergone complex chemical reactions,mainly mineral dissolution and mineral secondary action;Acid solution had an impact on the physical properties,microstructure and mechanical properties of sandstone,which was manifested in the reduction of macro mechanical parameters in varying degrees in the macro,and the change of micro structure and composition in the micro.(2)The quality,density,longitudinal and transverse wave velocity and triaxial compressive strength of freeze-thaw cyclic sandstone were analyzed,and the microstructure and failure mechanism of sandstone specimens were observed and analyzed by scanning electron microscope(SEM).After the freeze-thaw cycle,the surface mesostructure of sandstone has changed to some extent.Under the action of freeze-thaw cycle,a certain frost heaving force was generated in the rock.Under the repeated action of this frost heaving force,the macro aspect was realized as the reduction of rock strength,the continuous decline of quality and wave velocity,the increase of deformation,the fracture and spalling of rock and other phenomena,In the micro view,it shows the change of micro structure.(3)The quality,density,longitudinal and shear wave velocity,and triaxial compressive strength of the sandstone after acid corrosion and freeze-thaw cycles were analyzed,and the microstructure and failure mechanism of the sandstone test block were observed and analyzed by scanning electron microscope(SEM)equipment.The surface microstructure of the sandstone test block after immersion in acid solution and freezethaw cycle treatment was more obvious than that when the two act alone;Not a simple superposition of damage caused by acid etching and freeze-thaw cycles,it was an overall effect formed by the coupling of acid erosion and freeze-thaw cycles,which will aggravate the damage of rock structures.(4)Based on the Lemaitre strain equivalence hypothesis,it was assumed that the micro-element strength of the acid-corroded rock under the coupled action of temperature and confining pressure obeys the Weibull distribution.Continuous damage mechanics and statistical theory were used,and chemical damage variables,thermal damage variables and mechanical damage variables were introduced,under the condition that the microelement damage conforms to the DP criterion,the damage evolution equation and constitutive model of the acid-etched rock considering the coupling effect of temperature and confining pressure were constructed.The required model parameters were obtained by the method of theoretical derivation,and the model was verified based on the triaxial compression test data.The peak point of the experimental curve was compared with the peak point of the theoretical curve of the model,and the results show that the two were in good agreement.(5)Based on Lemaitre strain equivalent hypothesis theory,the deterioration degree and damage evolution law of rock materials were described by introducing chemical damage variables,freeze-thaw damage variables and mechanical damage variables,and the total damage variables of acid corroded rocks under the coupling action of freezethaw and confining pressure were deduced.The damage evolution equation and constitutive model of acid eroded rock under the coupling action of freeze-thaw and confining pressure were established by using the theory of continuous damage mechanics.Finally,the rationality and accuracy of the model were verified by using the triaxial compression test data of freeze-thaw rock.The peak point of the test curve was compared with the peak point of the model theoretical curve,and the results show that the two were in good agreement.(6)Based on Lemaitre’s strain equivalent hypothesis theory,the deterioration degree and damage evolution law of rock materials were described by introducing meso freezethaw damage variables and force damage variables that can reflect the process of rock freeze-thaw failure.Using the theory of continuous damage mechanics,the damage evolution equation and meso damage constitutive model of rock under the coupling of freeze-thaw and confining pressure were established.Finally,the rationality and accuracy of the model were verified by using the triaxial compression test data of freeze-thaw rock.The peak point of the test curve was compared with the peak point of the theoretical curve of the model.The results showed that they were in good agreement.The damage constitutive model can better reflect the stress-strain peak characteristics of rock during triaxial compression,and verify the rationality and reliability of the model and the method for determining model parameters.The model expands the damage model of rock under the coupling action of freeze-thaw and confining pressure,and further reveals the damage mechanism and failure law of rock under the coupling action of freeze-thaw and confining pressure. |
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