How local perturbation in regularity changes force chains in model granular soil under the shallow foundation

A phenomenon of the progressive failure in ground under the shallow foundation has been understood whereas its micro-mechanical mechanism is still under question. We examined confined buckling of particle force chains differently generated in two model assemblies. One model assembly contains particles packed regularly and the other contains the similar regularly packed particles with limited heterogeneity. The photoelastic measurement technique was employed to visualize the contact force transmission within particle assemblies. Three model assemblies bounded by a steel frame were built by stacking bi-dimensional circular particles made of Polytetrafluoroethyleneand Polycarbonate elastomer. Each particle was coated by a thin photoelastic sheet so that the force transmission among particles can be visualized. In a contacted particle, both magnitude and orientation of principal stress difference can also be measured via the photoelasticity technique. The model assembly was subjected to incremental surface loading, which simulates a bearing capacity problem of the shallow foundation on granular soils. A local perturbation can cause significantly different pattern of the contact force chains in the regular assembly than the assembly without perturbation.