The Development of a Micromechanical Apparatus Applying Combined Normal–Shear–Bending Forces to Natural Sand Grains with Artificial Bonds

Abstract

Natural soils are often cemented, and there has been a need to better understand and properly model their behavior for the safe design and assessment of critical infrastructure. This necessitates the study of cemented soils at the scale of the grain. In this study, a new-generation apparatus is presented that is capable of conducting complex load path tests on two natural sand grains cemented with an artificial bonding component. Thus, the apparatus gives the opportunity to obtain insights into the micromechanics of cemented soils/weak rocks and contribute to the development of more accurate models to be utilized in the discrete element analysis of geomaterials. Apart from the presentation of the major technical features of the new apparatus, a description of the methods which were used for specimen preparation and mounting, as well as a preliminary set of experiments, are presented and discussed in this note.

Micromechanical behaviour in shearing of reproduced flat LBS grains with strong and weak artificial bonds

“…A new micromechanical apparatus for investigating the behaviour of artificially bonded sand-sized grains under normal, shear and bending loads was developed by Wang et al (2019) at City University of Hong Kong. The apparatus has two loading systems in the vertical and horizontal directions with a linear stepping motor and a load cell in each direction.…”

“…The apparatus has two loading systems in the vertical and horizontal directions with a linear stepping motor and a load cell in each direction. Based on these preliminary results and the built of the apparatus by Wang et al (2019), significant modifications were required, in terms of mechanical arrangement of the apparatus and the testing methodology so that the upgraded apparatus can provide adequate precision of forces and displacements in order to obtain high quality data in terms of forcedisplacement relationship and subsequently contact stiffness of the bonded specimens.…”

“…Such an upgrade to the loading arm was needed to increase the stiffness of the apparatus and also to enable the apparatus to carry out cyclic shearing tests. In the previous version of the apparatus by Wang et al (2019), the loading arm was very long (~10mm) which might induce additional flexibility during shearing. Shortening the loading arm and fixing it at both ends increased the tangential stiffness of the apparatus.…”

“…Using sand grains bonded with gypsum plaster, Wang et al (2017) highlighted the cemented particle crushing behaviour by defining different modes of failure. Wang et al (2019) conducted complex loading tests by imposing shearing and combined shearing and bending loads on bonded grains at 50N normal load. These studies indicated that bond thickness and the morphology of the grains at the boundary with the bonding material are key factors which influence the strength parameters and mechanical behaviour of the specimens.…”

“…The experiments were performed using a newly developed micromechanical loading apparatus for cemented grains, which provides high precision of force and displacement increment and so the quantification of contact stiffness of cemented grains is feasible, overcoming a limitation of the apparatus previously developed by Wang et al (2019).…”