| Soil-rock aggregate is a special kind of material,its property is between soil and stone,and it is widely distributed in nature.In recent years,as the country invests heavily in infrastructure,a large number of buildings and roads,bridges,tunnels and other projects,more and more people begin to find and contact the geological body.Soil-rock aggregate has certain disparity and uncertainty,and limited to the current understanding of the characteristics of the geological and engineering index,processing methods tend to be conservative.Therefore,the study of the physical and mechanical properties and deformation characteristics has important theoretical meaning and engineering value.In this paper,based on Chongqing metro line 10 from range Shang Wan road ~ Huan Shan park backfill soil sections,through theoretical analysis,laboratory test and numerical simulation method of PFC,and the using of MATLAB digital image processing,the author did a thorough research to the soil-rock-mixture of backfill soil section in mesoscopic mechanical characteristics.The main research and results of this paper are :(1)By the test of field sampling and screening sieving,we get the gradation curve of earth-rock aggregate,then configure different stone content(0%,10%,20%,30%,0%,50%,60%,70%,80%)of the test sample,and under different confining pressure(200 kPa,400 kPa,600 kPa to 800 kPa)indoor triaxial test.Results show that with the increase of confining pressure,soil-rock-mixture packing by the strain softening damage gradually transition to the strain hardening damage,the corresponding body strain by dilatancy transition to the shear shrinkage,and the higher the stone content,the lower confining pressure and strain softening of the more obvious dilatancy phenomena,while higher confining pressure and strain hardening of the weaker shear shrinkage phenomenon,at the same time with the sample of the stone content increased from 0% to 80%,the friction angle increase,while cohesive force decrease.(2)Using earth-rock aggregate after sieving,with different content of rock sample,and making digital collection,self-compiled program,then we use MATLAB software to make the digital image binary processing,get different stone content of soil-rock aggregate binary image,(3)According to binary map,we build up particle flow software(PFC2D)to carry out numerical simulation.Then according to the lab,it is concluded that stress strain curve,volume strain curve and c value to demarcate the microscopic parameters of model,and calculation model is established to simulate the indoor triaxial test process.The numerical simulation is set in different content of stone(200,400,600,800kPa),different loading speed(1 mm/min,1.5 mm/min,2 mm/min,3 mm/min),and different sizes(300×600 mm,450×900 mm,600×1200 mm,900×1800 mm),the three affecting factors are used to explore mesoscopic mechanics properties of soil-rock aggregate.(4)According to the results of numerical simulation 1)analysis of the axial strain-deviatoric stress curve,as the loading conditions are consistent,stone content of the model has a great effect on shear properties,the higher the stone content,the higher the peak value of deviatoric stress,as well as the model shows greater rigidity,shear stress and shear strain curve near elastic section with bigger slope,deviatoric stress peak value of the corresponding axial strain becomes smaller.From the analysis of the axial strain-volume strain curve,it shows that as the stone content increased gradually,transverse strain transforms gradually from shear contraction to shear dilatancy,namely,dilatancy is gradually enhanced.2)With the sample grading,load conditions,when the model size increases,the peak value of deviatoric stress shows a trend of decrease,the corresponding axial strain is less.For axial strain-deviatoric stress curve near elastic section,the change of model size has little influence on it,so,it can be assumed that the model size is irrelevant to the overall stiffness.From the analysis of axial strain and volumetric strain curve,as the size of the model increases,the shear volume decreases gradually,and the shear strength decreases.3)Under the loading rate,the axial strain-deviatoric stress curve went through two stages,namely initial faster-growing stress linear elastic deformation stage,and the latter the slower-growing stage.The main stress difference between the first stage and the second stage increases significantly with the loading rate,i.e.the initial elastic modulus of the sample is positively correlated with the loading rate.The sample’s body strain is mainly sheared at the beginning of loading,but then transit to dilatancy after a period of low confining pressure. |
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