Understanding the microscopic origin of behavior in particulate and particle-fluid systems such as granular materials, foams, and emulsions is of both practical and fundamental importance. In this internship project, we will investigate the mechanical behavior of an assembly of immersed gel beads (isodense) by ultrasound imaging (transient elastography) and rheology. Studying such a soft granular material or suspension is of interest not only for biomedical applications (muscles and tissues) and for geophysical implications (landslides), but is also relevant to the physics of complex systems where the transition from a liquid state to a solid state remains a highly topical issue. In this work, we will first use an ultrafast ultrasound scanner to monitor the low-frequency shear wave within an optically opaque dense gel bead packing generated by an oscillating plate. We are particularly interested in nonlinear response such as shear elastic softening and fracture dynamics as a function of shear amplitude, and monitor the structure change due to plastic rearrangements of particles by ultrasonic imaging.