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arxiv: 1907.10924 · v1 · pith:MZTRH7JQnew · submitted 2019-07-25 · ❄️ cond-mat.soft

Influence of the size of the intruder on the reorganization of a 2D granular medium

Aymeric Merceron , Alban Sauret , Pierre Jop This is my paper

Pith reviewed 2026-05-24 16:12 UTC · model grok-4.3

classification ❄️ cond-mat.soft
keywords granular packingintruder withdrawalarch formationreorganization dynamics2D granular mediumavalanche eventssize ratio
0
0 comments X

The pith

Small intruders in a 2D granular packing form arches that periodically collapse and drive larger rearrangement events.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper investigates how withdrawing an intruder of varying size rearranges a vertical two-dimensional granular packing over long times and in short-term avalanches. When the intruder is small enough relative to the particles, arches form above it, build stress, and then destabilize in cycles that produce bigger particle rearrangements than occur with larger intruders. A sympathetic reader would care because the size ratio appears to switch the packing between continuous local adjustments and episodic large-scale reorganizations. This distinction matters for any process where an object moves through or is removed from a bed of grains, such as mixing, extraction, or flow initiation.

Core claim

For intruders small enough relative to the surrounding particles, arches form in the packing and periodically destabilize, thereby controlling the reorganization dynamics through larger rearrangement events; larger intruders produce different, less episodic dynamics without these periodic arch failures.

What carries the argument

The intruder-to-particle size ratio, which sets the condition for arch formation and its periodic destabilization above the intruder.

If this is right

  • Reorganization shifts from local continuous motion to episodic large events once the intruder drops below a critical size ratio.
  • Arch destabilization events dominate the short-term avalanche statistics around the intruder.
  • The long-term compaction or void distribution left in the packing after many withdrawals depends on intruder size.
  • The frequency of large rearrangements scales with the build-up and release cycle of the arches.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same size-ratio threshold might control whether an object sinking or rising through a granular bed produces sudden slips or steady motion.
  • Changing particle friction or polydispersity could move the critical size ratio at which arches begin to appear.
  • In industrial settings such as silo discharge or granular mixing, deliberately choosing intruder size could suppress or promote sudden rearrangements.

Load-bearing premise

The observed arches and their periodic collapses arise specifically from the intruder being small enough compared with the particles rather than from other experimental details such as how the packing was prepared or the values of friction and boundaries.

What would settle it

Running the withdrawal experiment with a small intruder and finding neither arch formation nor a measurable increase in the size or frequency of large rearrangement events compared with large-intruder runs would falsify the claimed link.

read the original abstract

We consider the rearrangements of a vertical twodimensional granular packing induced by the withdrawal of an intruder. Here, we focus on the influence of the size of the intruder on the reorganization process. The long term evolution of the granular packing is investigated as well as the avalanche dynamics that characterize the short term rearrangements around the intruder. For small enough intruder, we observe the formation of arches that periodically destabilize and influence the reorganization dynamics of the two-dimensional packing through larger rearrangement events.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript reports an experimental study of intruder withdrawal from a vertical 2D granular packing, focusing on the effect of intruder size. The central claim is that sufficiently small intruders lead to the formation of arches that periodically destabilize, producing larger rearrangement events that govern both the short-term avalanche dynamics around the intruder and the long-term reorganization of the packing.

Significance. If the size-ratio dependence is isolated from other experimental variables, the result would add a concrete observation to the literature on intruder-induced granular rearrangements and arching phenomena. The work is observational rather than theoretical and does not claim parameter-free derivations or machine-checked proofs.

major comments (2)
  1. [Methods] Methods section: no description is given of whether packing preparation protocol, particle friction, withdrawal speed, or lateral boundary conditions were held fixed while intruder diameter was varied. Without such controls, the attribution of arch formation and periodic destabilization specifically to the intruder-to-particle size ratio remains unisolated, directly undermining the causal claim in the abstract.
  2. [Results] Results section: the abstract states an observational claim but supplies no quantitative measures (e.g., arch lifetime statistics, event-size distributions, or size-ratio thresholds with error bars). The absence of these data prevents verification that the reported larger rearrangement events are systematically linked to small intruders rather than to uncontrolled variables.
minor comments (1)
  1. [Abstract] Abstract: the phrase 'for small enough intruder' is used without indicating the range of size ratios explored or the criterion used to define 'small enough'.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and the constructive comments on our manuscript. We address each major comment below and indicate the revisions that will be incorporated in the next version.

read point-by-point responses

  1. Referee: [Methods] Methods section: no description is given of whether packing preparation protocol, particle friction, withdrawal speed, or lateral boundary conditions were held fixed while intruder diameter was varied. Without such controls, the attribution of arch formation and periodic destabilization specifically to the intruder-to-particle size ratio remains unisolated, directly undermining the causal claim in the abstract.

    Authors: We agree that the Methods section must explicitly document the experimental controls. In the original experiments the packing preparation protocol, the particles (hence friction), the withdrawal speed, and the lateral boundary conditions were all held fixed while only the intruder diameter was varied. We will revise the Methods section to include a dedicated paragraph stating these controls and confirming that the intruder-to-particle size ratio is the sole variable under study. revision: yes

  2. Referee: [Results] Results section: the abstract states an observational claim but supplies no quantitative measures (e.g., arch lifetime statistics, event-size distributions, or size-ratio thresholds with error bars). The absence of these data prevents verification that the reported larger rearrangement events are systematically linked to small intruders rather than to uncontrolled variables.

    Authors: The manuscript is primarily observational, yet the full text already contains repeated realizations that allow extraction of the requested statistics. We will add a new subsection (or expand the existing Results) that reports (i) distributions of arch lifetimes, (ii) event-size histograms for small versus large intruders, and (iii) the critical size-ratio threshold together with error bars obtained from multiple independent packings. These additions will directly address the need for quantitative verification. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental observations only

full rationale

This is a purely experimental granular-media study reporting direct visual observations of intruder-induced rearrangements and arch formation. The abstract and described content contain no derivations, no equations, no fitted parameters presented as predictions, and no self-citation chains used to justify a central claim. The reader's circularity score of 0.0 is therefore confirmed; the paper makes no load-bearing mathematical or definitional reductions that could be circular.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

The central claim rests on the experimental observation that arch formation occurs below a critical intruder size. No free parameters, new axioms, or invented entities are introduced in the abstract.

pith-pipeline@v0.9.0 · 5604 in / 1012 out tokens · 19506 ms · 2026-05-24T16:12:48.751868+00:00 · methodology

discussion (0)

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Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

  • Foundation/AlexanderDuality.lean alexander_duality_circle_linking unclear
    ?
    unclear

    Relation between the paper passage and the cited Recognition theorem.

    For small enough intruder, we observe the formation of arches that periodically destabilize and influence the reorganization dynamics... avalanche size distributions... power law... slope becomes less steep for the small intruders (from -2.6 to -1.6)

  • Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear
    ?
    unclear

    Relation between the paper passage and the cited Recognition theorem.

    The formation of arches... jamming events... critical size beyond which jamming events become rare

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

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