Presentation Information
[PPS04-P01]Laboratory Experiments on the Compaction Behavior of Hierarchical Granular Layers: Comparison with a Model
*Tomomi Omura1, Hiroaki Katsuragi2, Yukari M Toyoda3 (1.Osaka Sangyo University, 2.Osaka University, 3.Astrobiology Center)
Keywords:
planetesimals,dust,hierarchical structure,compaction,laboratory experiment
The physical properties of planetesimals, such as mechanical strength and thermal properties, depend on the granular structure of the constituent particles. The granular structure evolves from its initial state through compaction, which is mainly driven by self-gravity. Recently, gravitational instability in protoplanetary disks has been widely discussed as a mechanism for planetesimal formation. Planetesimals formed through gravitational instability are expected to have a hierarchical granular structure consisting of agglomerates (pebbles) composed of dust grains. The compaction of hierarchical granular layers proceeds through the following three-stage process, as demonstrated by numerical simulations [1]: (1) rearrangement of the aggregate (pebble) packing structure (2) plastic deformation of the aggregate (3) elastic deformation of constituent particles. This three-stage process is qualitatively consistent with previous experimental studies. However, the relationship between pebble characteristics and compaction behavior has not been sufficiently investigated. We aim to address this question experimentally. Although a model equation proposed in [1] successfully reproduces the compaction curves at each stage based on pebble characteristics, its applicability to realistic particle layers remains unclear. In this presentation, we discuss the applicability and limitations of the existing model based on comparison with our experimental results.
Compaction experiments were conducted using a universal testing machine (Shimadzu, AG-X). The pebbles used in this study were agglomerates with diameters of 1–2 mm, composed of glass beads with a diameter of 4.2 μm (Potters Ballotini, EMB-10). These agglomerates naturally formed within the glass beads during storage in the laboratory. The pebble filling factor was estimated to be 0.39 from measurements of ~4 mm agglomerates. When uncertainties in the volume and mass measurements are considered, the estimated filling factor ranges from 0.3 to 0.6. Pebble layers were compacted with a piston mounted on the testing machine at a loading rate of 10 μm/s, reaching a maximum pressure of 6 × 106 Pa. For comparison, the same experiments were performed on a homogeneous particle layer composed of glass beads that were sieved to remove agglomerates.
The compaction curves, i.e. the relationship between the pressure applied to the sample layer and the filling factor of the sample, show that pebble layer required higher pressures than the homogeneous layer until the compaction proceeded significantly. To examine structural evolution in this pressure range, samples subjected to maximum pressures within this range were observed using a X-ray CT scanner (NAOMi-CT 3D-M). The observations indicate that compaction in this regime proceeds through pebble deformation.
The overall curve shape in the regime could be reproduced by the model proposed in [1], but only after significant parameter adjustment. The compaction curves could not be reproduced quantitatively using the measured and assumed parameter values. Therefore, we treated the pebble filling factor and the unmeasured compression onset displacement δagg,0 as free parameters. The best agreement was obtained when the pebble filling factor was set to 0.56 and δagg,0 was taken to be three times larger than the value assumed in the model. Increasing δagg,0 further allowed quantitative agreement with the experimental data, even at lower pebble filling factors. In this presentation, we discuss the physical plausibility and implications of these parameter values.
References: [1] Arakawa et al., 2025, EPS, 77:89
Compaction experiments were conducted using a universal testing machine (Shimadzu, AG-X). The pebbles used in this study were agglomerates with diameters of 1–2 mm, composed of glass beads with a diameter of 4.2 μm (Potters Ballotini, EMB-10). These agglomerates naturally formed within the glass beads during storage in the laboratory. The pebble filling factor was estimated to be 0.39 from measurements of ~4 mm agglomerates. When uncertainties in the volume and mass measurements are considered, the estimated filling factor ranges from 0.3 to 0.6. Pebble layers were compacted with a piston mounted on the testing machine at a loading rate of 10 μm/s, reaching a maximum pressure of 6 × 106 Pa. For comparison, the same experiments were performed on a homogeneous particle layer composed of glass beads that were sieved to remove agglomerates.
The compaction curves, i.e. the relationship between the pressure applied to the sample layer and the filling factor of the sample, show that pebble layer required higher pressures than the homogeneous layer until the compaction proceeded significantly. To examine structural evolution in this pressure range, samples subjected to maximum pressures within this range were observed using a X-ray CT scanner (NAOMi-CT 3D-M). The observations indicate that compaction in this regime proceeds through pebble deformation.
The overall curve shape in the regime could be reproduced by the model proposed in [1], but only after significant parameter adjustment. The compaction curves could not be reproduced quantitatively using the measured and assumed parameter values. Therefore, we treated the pebble filling factor and the unmeasured compression onset displacement δagg,0 as free parameters. The best agreement was obtained when the pebble filling factor was set to 0.56 and δagg,0 was taken to be three times larger than the value assumed in the model. Increasing δagg,0 further allowed quantitative agreement with the experimental data, even at lower pebble filling factors. In this presentation, we discuss the physical plausibility and implications of these parameter values.
References: [1] Arakawa et al., 2025, EPS, 77:89