Direct shear tests on the effects of displacement rate and particle size ratio on the shear behavior of fine gravel-rubber mixtures

Abstract

Gravel-rubber mixtures (GRM) are eco-friendly materials created by combining gravel and granulated rubber, which are effectively used for geotechnical seismic isolation. The shear strength parameters of GRM are crucial for assessing its effectiveness in seismic isolation; however, the effects of displacement rate and particle size ratio are not yet fully understood. To investigate this, a series of large-scale direct shear tests were conducted, varying displacement rates, particle size ratios, rubber contents, and normal stresses. The results indicated that the displacement rates (0.1 mm/min to 4 mm/min) had a minimal impact on the shear strength and internal friction angle of GRM. However, cohesion increased significantly at displacement rates within 0.5 mm/min. Additionally, a higher displacement rate led to a marked reduction in the contraction of GRM, with the maximum difference reaching approximately 50 %. The shear strength of the mixtures decreased as rubber content increased, particularly with smaller rubber particles and lower normal stresses. Conversely, when the particle size ratio increased from 0.2 to 2, the shear strength of GRM improved by 6∼29 %, while the corresponding vertical displacement decreased by 38∼82 %. A notable increase in cohesion and a slight decrease in the internal friction angle were observed within a particle size ratio of 0.4. Furthermore, while the internal friction angle gradually decreased, the cohesion initially dropped (up to 20 % rubber content) before beginning to rise with increasing rubber content. The findings of this research will improve the understanding of the shear strength of GRMs.</p