Pfc Simulation Of The Mechanical Behaviors Of Loading And Unloading On Deep Artificial Frozenclay

The safety of the frozen soil wall and shaft lining is the most nuclear technology in freeze sinking project in deep alluvium,and in-depth understanding of the engineering properties is an important foundation for the design of the frozen soil wall and shaft lining.It has significant structural because of its special environment.The artificial deep frozen clay experienced loading and unloading process meanwhile the freeze sinking project.The structural of the deep undisturbed clay changed much after remodeling,which led to the macromechanic difference between the undisturbed clay and remolded clay.Therefore it is necessary to characterize the structural from the subtle concept of scale,researching on macroscopic and microscopic mechanical properties of loading and unloading process contribute to understand the mechanical properties essentially,which is significance for the design of soil wall and shaft lining.This paper carried out the following tasks(1):Quantitative analysis of the microscopic structure of the deep undisturbed clay and remolded clay through SEM image digital processing,building artificially deep frozen remolded clay and undisturbed clay of particles flow model, support vector machine prediction model Lib SVM of microscopic mechanical parameters were calibrated combined triaxial test data.(2)Designing loading and unloading numerical simulation for deep remolded clay and undisturbed clay at different temperature and confining pressure,getting the strength、deformation and evolution of the microstructure.(3)Triaxial tests were carried out for artificially deep frozen remolded clay at different temperature and confining pressure,comparing the results of numerical simulation and laboratory test.Conclusions as follows through these studies:(1) According to the IPP image processing results,the granules of artificial deep frozen remolded clay are mainly concentrated in the area below 1002mm,mainly located in the angle between 50°~70°,and the porosity is 0.25.The granules of artificial deep frozen undisturbed clay are mainly concentrated in the area below 1002mm,mainly located in the angle between 10°~50°,the porosity is 0.24. After microscopic mechanical effects analysis,the microscopic parameters obtained by support vector machine model can reflect deep mechanical properties of artificial frozen clay well.(2) The strain increased with time at loading phase of artificially deep remolded clay,the strain variation in constant lateral pressure coefficient loading phase is much larger than that at isostatic loading phase and vary lateral pressure coefficient loading phase;the strain variation of undisturbed clay is the same as the remolded clay at loading phase,except that the time and strain is less than the end of each stage.In the constant axial pressure and unload confining pressure process,the strain significantly increased with time increasing;the strain significantly uncreased with time increasing in constant confining pressure and unloading axial pressure process.(3) The strain increased linearly with partial stress increasing at constant lateral pressure coefficient loading phase of artificially deep frozen remolded clay.The strain increased with partial stress increasing at constant axial pressure and unloading confining pressure process,the relationship is strain hardening characteristics;the strain uncreased with partial stress uncreasing at unloading axial pressure and constant confining pressure process,the relationship is strain hardening characteristics.(4) The variation of the artificially deep frozen clay is the same as the remolded clay at constant lateral pressure coefficient loading phase,the strain increased with partial stress increasing in the early,and then uncreased with partial stress uncreasing after reaching the peak intensity,the relationship is strain softening.The variation is the same as the remolded clay at constant confining pressure and unloading axial pressure.(5) The structure of the artificially deep frozen remolded clay is the same as “drum” after loading;the structure of the artificially deep frozen undisturbed clay is “split state”,both of which you can see the contact force.The diameters of the “drum” is much larger after the unloading phase than that on the loading phase at unloading confining pressure and constant axial pressure process,the height is lower and contact force is more complete;the splitting crack of “split state” is bigger,sheat plane appears at the contact force. When the uninstall is complete,the effect of temperature on the peak strength and elastic modulus is linearly,the impact is greater than the effect of confining pressure.(6) Traixal unloading tests under constant axial pressure and unloading confining pressure、constant confining pressure and unloading axial pressure process were carried out on frozen clay to obtain the curves of stress-strain and strength、elastic modulus,obtaining the impact of confining pressure and freezing temperature on strength 、elastic modulus、deformation modulus,drawing the conclusion that freezing temperature is main factors than confining pressure.(7) According to the rusults of laboratory,the curves of stress-strain and sample failure modes are the same as numerical simulation.The strength under laboratory test condition is 4 percent lower than numerical simulation and elastic modulus is 24 percent higher under the constant axial pressure and unloading confining pressure process; the strength under Laboratory test condition is 5 percent lower than numerical simulation and elastic modulus is 15 percent higher under the constant confining pressure and unloading axial pressure process.