Transition of shear flow for granular materials in a numerical ring shear test
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ORIGINAL PAPER
Transition of shear flow for granular materials in a numerical ring shear test Zhibo Dong1,4 · Lijun Su1,2,3,4 · Chonglei Zhang1,2 · Zhenyu Liu1,4 · Siyou Xiao1,4 Received: 3 April 2020 / Accepted: 28 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The shear flow behaviors of granular materials exist widely in natural events. Ring shear tests based on the discrete element method were carried out to study the effects of shearing rate on the transition of quasi-static and slow flow phases of granular materials. The simulated results indicated that the shear stress and normalized volume increase linearly with the square of the shearing rate, and the two corresponding critical shearing rates are the same. Through the analysis of the μeff (I) rheology model, the micro-mechanism of the transition between the quasi-static and slow flow phase has been discussed quantitatively. Additionally, the critical shearing rate under different normal stress and rolling resistance friction coefficient were tested. It is found that the critical shearing rate augments with the increase in normal stress. However, it does not change with the increase of the rolling resistance friction coefficient of granular materials. The above work on the flow phase transition of granular materials can be helpful to study the mechanism of the starting stage of geological disasters, such as landslides and debris flows. Keywords Granular materials · Flow phases · Critical shearing rate · DEM · Ring shear test
1 Introduction The shear flow of granular materials widely exists in various natural events [1–5]. Granular flow can normally be divided into rapid flow, slow flow, and quasi-static flow, and it shows solid-like or liquid-like properties under different conditions, such as start-up and accelerated sliding stage of a landslide, which is a typical type of shear flow of granular materials [6–8]. The earliest work on the shear flow of granular materials can be traced to the 1950s. Bagnold [9] reported stress–strain relations of granular materials by using a rheometer. Since * Lijun Su [email protected] 1
Key Laboratory of Mountain Hazards and Earth Surface Processes, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu 610041, China
2
CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China
3
China-Pakistan Joint Research Centre On Earth Sciences, CAS-HEC, Islamabad, Pakistan
4
University of Chinese Academy of Sciences, Beijing 100049, China
then, laboratory experiments have developed rapidly. Various testing methods have been utilized to study the phase transition and properties of granular flow, such as annular shear cells, incline flows, and vertical chute flows [10, 11]. The ring shear test is the main method to determine the relationships between shear stress and shearing rate of particles. Savage [12] found the effect of shearing rate and volume fraction on the effective friction coefficient through ring shear tests.
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