| The soil is a natural loose granular medium, with solid, liquid and gas-phase, belonging todense material particles media. Meanwhile, The soil granular medium is composed ofdifferent sizes and shapes of particles gathered together to form a non-continuous body, itsmechanical properties associated with microstructures such as the particle size, shape,distribution and the link mode between the particles, and it has a very complex and uniquemechanical properties. It is significant to understand the soil granular medium from theperspective of microstructure, and it is not only beneficial to explain the internal mechanismof granular media system, but also conducive to provide a reasonable effective approach topractical geotechnical problems. In this paper, the study of soil particles medium onlyconsider solid phase, liquid and gas is not to consider, and the soil particles are approximatelycircular ideally. This kind of assumption can study well the soil effective stress (net of porepressure and water pressure) and deformation characteristics. Therefore, we use photo-elastictechnology test compression and shear visualization tests and analysis. The main results ofthis paper are the following aspects:(1) The force chain of particle system is distributed such as tree branches or mesh, in thecompression test force chain is mainly straight down, shear test is mainly tilted upward, andforce chain has unevenness distribution. The formation and disappearance of archingillustrate visually shear failure recombinant of particle systems. From the microscopic point ofview reveals the mechanism of shear dilatancy or contraction in granular media system is dueto the redistribution of the particles after the particles loose or tight each other because ofsqueezing and shear action. The initial state arrangement of the system, volume fraction,forms of the boundary loads, particle size and strengthening particles influence thedevelopment of force chain mesh.(2) Stress arching is one of the characteristics of granular media different from thecontinuous medium. This article prove existence of stress arching in sticky particles visually，its arch thickness has a direct relationship with section width of the pile, the granular layerthickness obviously impact the stress arching shape. With the boundary load increases, thestress arching limit damage will occur, but then it gradually formed a new arching structure,Size of boundary loads affects high of arching. Distance to diameter ratio affects formation ofstress arching, This paper considers qualitatively in diameter3mm particle system thatdistance to diameter ratio L/D is set to1:2is most reasonable.(3) Some photo-elastic images of compression and shear model are digital image analysized. Before the particle system is not applied boundary loads，the geometry of theinitial structural exists anisotropy. compression load enhance system anisotropy, shear loadweaken system anisotropy. Anisotropy of geometry in particles media affect the distributioninternal stress of system. Particle size and particle size distribution affect the anisotropy of thegeometry, thus affecting the stress distribution within the system.(4) The Changes of visualization displacement field in particle explains the conditions forthe formation of stress arching, the one is uneven displacement or relative displacementbetween the soil particles, another one is the presence of the arch of the foot support. Thisarticle fit the stress arch stress field to further elaborate discussion that boundary load size,granular layer thickness and distance to diameter ratio are the main factor of stress arching. |
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