Effective stress—the fraction of the total stress that is transmitted through the solid skeleton—controls the mechanical behavior of porous media, from land subsidence due to groundwater pumping to the cohesion of sand in sandcastles. Karl von Terzaghi, father of soil mechanics, introduced this concept a century ago [1]. Unveiling effective stress recognizes the powerful coupling among viscous, capillary, and frictional forces within fluid-filled porous media, especially granular media with strongly-coupled fluids [2]. However, effective stress remains a physical quantity that can only be calculated by subtracting pore pressure from the normal component of the stress tensor, or inferred from its “effect”, typically the solid skeleton deformation. Particularly challenging is capturing the evolution of effective stresses in path-dependent physical processes in porous media, such as friction, fracturing, creeping, plastic deformation, and multiphase flows. Here, we use photoelasticimetry to visualize the evolving effective stress field in fluid-filled granular media in processes that couple fluid flow and mechanical deformation. We hereby refer to this experimental method as photo-poromechanics. We design the fabrication processes, similar to “squeeze casting”, and produce millimeter-scale residual-stress-free photoelastic spheres with high geometric accuracy. We use color, for the first time, to quantify the forces acting on the particles over a wide range of forces, while using light intensity for a small range of forces. We then provide a first application of photo-poromechanics to illustrate the evolution of effective stress during 1-D consolidation: a process by which the stresses caused by a sudden load are gradually transmitted through a fluid-filled granular pack as the fluid drains and excess pore pressures dissipate. We show that compaction of the granular pack is concomitant with the emergence of particle-particle force networks, which originate at the top boundary (where the pore fluid seeps out) and propagate downwards through the pack as the pore pressure gradually dissipates (Figure 1). Our novel technique provides a powerful experimental model system to study the strong coupling of solid and fluid in granular media.