The micro-mechanical behaviour of sand–rubber mixtures under shear : An experimental study based on X-ray micro-tomography

The micromechanical behaviour of two sand–rubber mixture samples (i.e., a glass bead–rubber mixture sample (GB–R) and a Leighton Buzzard sand–rubber mixture sample (LBS–R)) under triaxial compression is investigated using X-ray micro-CT (μCT). Both samples contain sand and rubber grains with similar size and have a rubber content of 30% by mass. The results are compared to those of two pure sand samples (i.e., GB and LBS). Both sand–rubber mixture samples are found to exhibit a significantly lower strain localisation than the pure sand samples. The average coordinate number (CN) of sand–sand contacts of the sand–rubber mixtures experiences a significant decrease at the late shear stage, although volumetric compression of the samples occurs. Meanwhile, sand–sand contact fabrics of the sand–rubber mixtures are found to remain almost unchanged throughout the test, with an anisotropy degree of around 0.04 for GB-R and −0.15 for LBS-R, respectively. In contrast, increasing contact areas and bias towards the major principal direction of sand–rubber contacts are observed in the sand–rubber mixtures as shear progresses, with the maximum anisotropy degree of about 0.27 for GB-R and 0.15 for LBS-R, respectively. Moreover, large-sized and small-sized sand–rubber contacts are found to concentrate towards the major and minor principal directions, respectively, throughout the test. The experimental observations highlight the important role of sand-rubber contacts in the stress-transmission behaviour of sand-rubber mixtures.