![]() This length is strongly connected to the saturation profile. This is consistent with the idea that, under fluid activity, the puffed rice collapses into its gradually wetting micropores. Since the displacement drops are much smaller than a typical grain, we assume that the micropores control the crushability of puffed rice. This double porosity is common for geomaterials, such as aggregate packs of rockfill dams ( 17), whose hydromechanical collapses motivated this study. Therefore, a pack of puffed rice has two characteristic sizes: a macropore size defined by the voids between the grains (of the order of a typical centimeter grain) and a micropore unit size. 3B, showing pore unit sizes mostly under a millimeter. Using these images, we manually measured over 300 micropore unit sizes, as given by the histogram in Fig. Therefore, to identify the microscopic feature potentially related to these drops, we took more than 15 slices of puffed rice grains and imaged them using a digital microscope, as shown in Fig. 2B that the displacement drops associated with the ricequakes are much smaller than the size of a single puffed rice grain. We note from the spatiotemporal plot in Fig. As seen from this figure, the delay times increase mostly linearly with time. The delay times between consecutive quakes can thus be unequivocally measured, as plotted in Fig. These incremental collapses synchronize perfectly with the instances of stress drops and acoustic bursts, thus all associated to the so-called ricequakes. The downward motion of the upper part of the pack shows recurring incremental drops interluded by creeping compaction periods. This occurred while the interface between the fully soaked and unsaturated parts of the pack remained closely stationary. As revealed by this figure, while the upper unsaturated pack significantly compacted over time, it collapsed almost as a rigid body motion into the lower fully saturated zone. 2A (here focusing on the time after the sample had established the recurring ricequakes). 2B) of the fabric along a central vertical line in Fig. To analyze the local vertical deformations across that region, we formed a spatiotemporal plot ( Fig. To discern the principal mechanism controlling this phenomenon, we used a Hirox KH-8700 digital microscope and recorded the deformation in the small interfacial region between the fully soaked and dry parts of the material, as seen in Fig. It is therefore likely that the ricequakes we find in partially soaked cereals may also develop in wet crustal rocks under experimentally inaccessible geological conditions. The testing of puffed cereal grains, however, is simpler as they are highly porous, brittle, and soft, which renders their compaction feasible within limited spaces and short time scales suitable for laboratory experiments. Following these first observations with puffed rice, the compaction of dry snow also disclosed similar patterns ( 11)-this is likely because rocks, dry snow, and cereals all share the properties of brittle porous media. Specifically, dry cornstarch, carbomer, and silicone have been used to demonstrate transient deformations in correspondingly brittle, semibrittle, and ductile crustal rocks ( 7), while cereal (puffed rice) has been used to reveal previously hidden propagating compaction patterns in dry porous media ( 8– 10). The substitution of subject materials by surrogate materials has been widely effective in science.
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