Uniaxial Compression of Photoelastic Granular Systems Around a Fixed Pin

The jamming transition—the onset of mechanical stability in granular systems—is typically controlled by packing fraction or applied stress, but the degree of quenched disorder is also a key factor. This is often introduced by fixing the positions of a subset of particles, known as pins, which can serve as a tool to tune the critical behavior and properties of amorphous materials. Here, we experimentally investigate how these pins affect the jamming transition as controlled by packing fraction. Our experiments utilize uniaxial compression on two-dimensional arrangements of bidisperse photoelastic particles, which allows for the direct visualization of contact forces. We observe that the force chain network is dramatically shifted even by a single pin, making it more likely for nearby particles to carry a stronger load. Our analysis of the force chain network, contact number, and pressure evolution reveals a rich, organized structure in the dynamical network heatmaps surrounding the fixed pin.