Effects of compaction effort, inclusion stiffness, and rubber size on the shear strength and stiffness of expansive soil-rubber (ESR) mixtures

The effects of compaction effort, inclusion stiffness, and rubber size on the shear strength and stiffness of expansive soil-rubber (ESR) mixtures was evaluated in this study in undrained axisymmetric compression. The materials tested included an expansive soil from Loveland, Colorado; two granulated rubber samples with 4.8 or 6.7 mm nominal maximum particle size; and a 50/50 mix of broken auto glass and crushed bottle glass. The effect of compaction effort was investigated by preparing and testing identical ESR mixtures compacted to either 95% of the standard or modified Proctor maximum dry densities at optimum water content. The effect of granulated rubber size was investigated by preparing and testing specimens with either 4.8 or 6.7 mm granulated rubber. The effect of inclusion stiffness was investigated by replicating the gradation of the 6.7 mm granulated rubber with two types of glass and testing an expansive soil-glass (ESG) mixture compacted to 95% of the standard Proctor maximum dry density for the ESG mixture. Specimens were evaluated for strength and stiffness by performing isotropically consolidated undrained triaxial tests at a mean effective stress equal to 25 kPa. Peak and critical state friction angles increased with increasing compaction of the ESR specimens in addition to a slight increase in stiffness. The stress-strain response is shown to be similar for both sizes of granulated rubber but the 6.7 mm granulated rubber particle size resulted in slightly higher peak and critical state friction angles. The stiffness of the inclusions is shown to change the material stress-strain response and stiffness substantially. © 2014 American Society of Civil Engineers.