Compressibility and strength of pebble piles

¹ Department of Aerospace Science and Technology, Politecnico di Milano, Via La Masa 34, Milano 20156, Italy
² Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP, Paseo del Bosque S/N (1900), La Plata, Argentina
³ Institute of Geophysics and Extraterrestrial Physics (IGEP), Technische Universität Braunschweig, Mendelssohnstraße 3, 38106 Braunschweig, Germany
⁴ Space Research & Planetary Sciences, Physics Institute, University of Bern, Gesellschaftsstrasse 6, Bern 3012, Switzerland

^★ Corresponding author: irinaluciana.sansebastian@polimi.it

Received: 4 July 2025
Accepted: 7 October 2025

Abstract

Context. Pebbles play a crucial role in planetary and planetesimal formation, as planetesimals and their remnants form from the gravitational collapse of a pebble cloud. Understanding the compressibility and strength of pebble piles is essential not only for elucidating these processes, but also for collisional evolution studies.

Aims. We aim to characterise the compressibility and tensile strength of pebble-pile samples under static compression.

Methods. We generated different-sized silica pebbles in the laboratory to assemble pebble-pile samples. The samples were compressed to derive their crush curves, then determine the tensile strength of the compressed samples using the Brazilian disk test. Additionally, we calculated the tensile strength through discrete element method simulations (DEM) and compared the results with our experimental findings.

Results. We obtain a new empirical relation linking tensile strength with the volume filling factor, consistent with previous results at low pressures but extended to higher compaction levels. Our findings show that tensile strength is independent of pebble size within the tested range. We also establish a new relationship for tensile strength as a function of pressure in pebble piles, which provides a better fit at higher pressures than previous approximations. The DEM simulations reproduce experimental results with good agreement.

Conclusions. The tensile strength of pebble piles, at moderate to high compaction, converges with those of dust aggregates, indicating partial or complete disintegration of the pebbles. Our results provide physically consistent scaling laws that describe relationships between pressure, porosity, and tensile strength.