The formation mechanism and evolution of force chain in the granular media system of fault fracture zone are important foundations for studying the occurrence of geological disasters such as creep

stick-slip and earthquake. By photo-elastic test device of particles under biaxial loading and bilateral flowing conditions

the macro-mechanical characteristics

the network structure and evolution

the spatial distribution and strength of force chain in the fracture zone are studied under shear. The results show that in fault fracture zone

the interaction between particles of rock mass is transmitted through the force chain. There are easy sliding section and non-easy sliding section between the fracture zone and the fault-induced fracture zone

which reveals the non-uniform characteristics of spatial deformation of the fracture zone under shear. The rearrangement of rock particles in the fracture zone results in the dynamic evolution of easy sliding sections and non-easy sliding sections. The larger-sized breccia particles in the fracture zone carry the main compression and friction between the upper and lower plates of the fault

which plays the role of “skeleton support”. With the increase of shear force

the direction of the strong force chain is deflected in the vertical direction. Rock particles near the middle of the fracture zone are more likely to be destroyed

fractured and rearranged when the fault is in a high stress state

which results in the change of spatial orientation of strong force chain. With the increase of vertical load

the spatial orientation of strong force chain changes from obvious anisotropy to uniform isotropy. The change of vertical load has little effect on the force chain ratio and the distribution of particle contact force frequency in fault fracture zone

but has great influence on the spatial distribution and strength of the force chain.