Study On Particle Breakage And Wetting Deformation Characteristics Of Soft Rock Filler Under The Equal Principal Stress Ratio Path

In recent years,with the vigorous promotion of "green and environmentally friendly" transportation construction,more and more soft rock crushed stone materials generated from tunnel excavation and other engineering projects are used for roadbed filling.Soft rock fillers have low strength,poor water rationality,and complex mechanical properties,which are prone to particle breakage under external forces and become more obvious after wetting with water.The internal stress development of actual roadbed filling engineering is close to the loading path of equal principal stress ratio,and the change in stress state will change the mechanical properties of rock and soil.The fragmentation and deformation of soft rock particles are dependent on the stress path;The softening of particles in contact with water is the main factor affecting the deformation difference between rock and soil before and after immersion.Poor control of wetting deformation will lead to damage and failure of the roadbed.However,there is currently a lack of systematic and in-depth research on the fragmentation and wetting deformation laws of soft rock filling particles in the roadbed under medium principal stress ratio paths.Therefore,this article conducts triaxial tests on soft rock fillers under equal principal stress ratio loading paths under two states of air drying and saturation,exploring the development law of deformation and particle breakage.Combined with PFC numerical simulation software,analysis and experiments are conducted to obtain the laws of particle breakage and wetting deformation of soft rock fillers under equal principal stress ratio paths.The main research conclusions are as follows:(1)The mineral composition of soft rock samples was analyzed through uniaxial compressive strength test and XRD test;By using a triaxial instrument,equal principal stress ratio loading tests were carried out on air dried and saturated samples,in which the influence of rubber film insertion on volumetric measurement results was eliminated through isotropic consolidation tests.Preliminary analysis of the test data shows that the stress-strain curves of air dried and saturated samples are roughly similar.With the constant increase of the principal stress ratio R,the partial stress axial strain curve gradually transits from a power function type to a hyperbolic type,and the axial strain volume strain relationship curve is approximately linear.The samples show volume compression during compression,and the strain value of air dried samples is always less than that of saturated samples under the same stress state change.(2)The samples under specific stress levels were screened for particles,and the particle breakage rates of air dried and saturated samples under different stress state changes were obtained.It was found that the particle breakage rate of soft rock was dependent on the stress path.The particle breakage rate of air dried and saturated samples was a hyperbola function with the principal stress ratio,and an exponential function with the average principal stress,A prediction model for the fragmentation rate of soft rock particles under air drying and saturation conditions was proposed regarding the principal stress ratio and average principal stress.(3)The relationship between particle breakage and axial deformation of air dried and saturated samples is approximately hyperbola;The relationship between particle breakage rate and volumetric strain is approximately linear,and is not affected by stress paths.A strain prediction model for air dried and saturated samples based on particle breakage is proposed.The predicted values and experimental values are compared and their errors are analyzed.The maximum error value under different principal stress ratio paths is around 15%,achieving more accurate prediction of the stress-strain relationship of soft rock samples.(4)Under different loading paths with equal principal stress ratios,the wetting axial strain of the sample increases as a exponential function function with the stress level,and the wetting volume strain increases linearly with the stress level;Comparing the grading curves of air dried and saturated samples under the same stress state changes,it was found that the grading of soft rock changes significantly before and after immersion;By comparing the particle breakage rates of air dried and saturated soft rocks under the same stress conditions,the wetting particle breakage rate of soft rocks is obtained.The data results show that the wetting particle breakage rate is an exponential function of stress level;The wetting axial and wetting volume changes of the sample are approximately linearly related to the fragmentation of wetting particles.(5)The PFC numerical simulation software was used to simulate the deformation and particle breakage of the sample during the loading process with equal principal stress ratio.Two sets of microscopic parameters were obtained through parameter calibration,which were consistent with the indoor test results.The particle cluster unit was introduced using Fish language to achieve particle grading statistics.The stress-strain curve in the numerical experiment was roughly the same as the particle breakage,and the variation pattern of particle breakage rate was basically consistent with the indoor test,At the same time,the process of particle changes in the sample was analyzed from a microscopic perspective,and the number of particle cracks and displacement field inside the sample were statistically analyzed.