On the Characterization of Lifting Forces During the Rapid Compaction of Deformable Porous Media

In a recent paper, Wu (2005, "Dynamic Compression of Highly Compressible Porous Media With Application to Snow Compaction," J. Fluid Mech., 542, pp. 281-304) developed a novel experimental and theoretical approach to investigate the dynamic lift forces generated in the rapid compression of highly compressible porous media, (e.g., snow layer), where a porous cylinder-piston apparatus was used to measure the pore air pressure generation and a consolidation theory was developed to capture the pore-pressure relaxation process. In the current study, we extend the approach of Wu to various porous materials such as synthetic fibers. The previous experimental setup was completely redesigned, where an accelerometer and a displacement sensor were employed to capture the motion of the piston. The pore-pressure relaxation during the rapid compaction of the porous material was measured. The consolidation theory developed by Wu was modified by introducing the damping effect from the solid phase of the porous materials. One uses Carman-Kozeny's relationship to describe the change in the permeability as a function of compression. By comparing the theoretical results with the experimental data, we evaluated the damping effect of the soft fibers, as well as that of the pore air pressure for two different porous materials, A and B. The experimental and theoretical approach presented herein has provided an important methodology in quantifying the contributions of different forces in the lift generation inside porous media and is an extension of the previous studies done by Wu.