Paper Number
PO28                         My Program 

Session
Poster Session

Title
Unifying intrusion dynamics in granular media for space exploration

Presentation Date and Time
October 16, 2024 (Wednesday) 6:30

Track / Room
Poster Session / Waterloo 3 & 4

Authors (Click on name to view author profile)

1. Ruck, John G. (University of Pennsylvania, Earth & Environmental Science)
2. Pradeep, Shravan (University of Pennsylvania, Earth and Environmental Science)
3. Bush, John (University of Southern California)
4. Jerolmack, Douglas J. (University of Pennsylvania, Department of Earth and Environmental Science)

Author and Affiliation Lines (in printed abstract book)
John G. Ruck¹, Shravan Pradeep¹, John Bush² and Douglas J. Jerolmack^1
1Earth & Environmental Science, University of Pennsylvania, Philadelphia, PA 19104; ²University of Southern California, Los Angeles, CA

Speaker / Presenter 
Ruck, John G.

Keywords
experimental methods; dense systems; future of rheology; particles; space applications

Text of Abstract
As sand transitions from loose to very tightly packed, its effective friction can change by a factor of 5. Loose sand is weak and compacts under a load, but fails gradually. Tightly packed sand is strong and dilates under a load, failing catastrophically. The classic critical state soil mechanics approach is to treat this behavior using a dilatancy angle, which predicts a symmetric increase or decrease in friction µ as volume fraction F increases or decreases from a critical value Fc that separates dilation from compaction. We find something different. We report on vertical intrusion experiments performed by a robotic leg - previously used for measuring soil strength - in a custom fluidized bed of frictional granular materials. This approach allows us to carefully observe how µ changes over the widest possible range in F and examine the material controls on it. We intrude into distinct materials, including silica sand, glass beads, and LHS-1 (lunar regolith simulant), over each specific attainable range in F. Angularity and polydispersity were found to have notable effects on µ and F. By accounting for how material properties control F, we collapse our intrusion data onto a universal curve. The way µ controls material strength is primarily through its control on F. Unifying these intrusion dynamics in granular materials presents new potential for predicting rheology in unknown environments, useful for understanding erosion thresholds of soil and river beds, for mobility on granular terrain, and for the exploration of other planets.