31 Oct 2020

31 Oct 2020

Review status: this preprint is currently under review for the journal ESurf.

Controls on the rates and products of particle attrition by bed-load collisions

Kimberly Litwin Miller1,2 and Douglas Jerolmack2 Kimberly Litwin Miller and Douglas Jerolmack
  • 1California Institute of Technology
  • 2University of Pennsylvania

Abstract. River rocks round through the process of impact attrition, where energetic collisions during bed-load transport induce chipping of the grain surface. This process is also important for bedrock erosion. Although previous work has shown that impact energy, lithology and shape are controlling factors for attrition rates, the functional dependence among these quantities is not settled. Here we examine these factors using a double-pendulum apparatus, that generates controlled collisions between two grains under conditions relevant for bed-load transport. We also determine the grain-size distributions (GSDs) of the attrition products. Two experimental results appear to support previous treatments of impact erosion as brittle fracture in the purely elastic regime: (i) mass loss is proportional to kinetic energy, and this proportionality is a function of previously identified material properties; and (ii) attrition product GSDs are well described by a Weibull distribution. Other observations, however, including the development of shallow and surface-parallel cracks, indicate that the common fatigue failure model is inappropriate. Rather, we propose that Hertzian fracture is the dominant mechanism that distinguishes chipping from fragmentation. We also identify an initial phase of rapid mass loss in which attrition is independent of energy and material properties; this is a shape effect associated with removal of very sharp corners. The apparent universality of both mass loss curves and attrition-product GSDs requires further investigation. Nonetheless, these findings are useful for interpreting the contribution of in-stream attrition to downstream fining and the production of sand, resulting from bed-load transport of river pebbles.

Kimberly Litwin Miller and Douglas Jerolmack

Status: open (until 12 Mar 2021)
Status: open (until 12 Mar 2021)
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Kimberly Litwin Miller and Douglas Jerolmack

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Binary Collisions Data Kimberly Litwin Miller

Kimberly Litwin Miller and Douglas Jerolmack


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Short summary
We conducted experiments to investigate the mechanics of sediment attrition due to collisions with the channel bed during downstream transport. During this process, the grains become rounder and smaller, changing the overall distribution of sediment in the river. In this work we examine how material properties play a role in the breakdown of sediment due to energetic collisions as well as the fine particles that are produced when chipped off of larger grains.