Experimental Evaluation of Mobilized Friction Angle of Sandy Soil-Rubber Mixtures for Different Loading Stress Paths

Tire-derived aggregates mixed with granular soils are amongst the new materials with different characteristics, as compared to the base materials, which are being used more commonly with the increase of waste rubbers and tires. These lightweight materials, having controlled compressibility, could be used in civil engineering infrastructures, road construction, and geotechnical structures. Up to now, limited experimental studies have been performed to present optimum mixing ratio of waste rubber and sand to attain the engineering purposes including the maximum bearing capacity and the most proper compressibility. Nevertheless, determination of a specific mixing ratio and identification of shear strength parameters of sand-rubber mixtures under different stress paths needs further study. In this research, results of triaxial tests, considering constant radial stress (CRS) and constant axial stress (CAS) paths on the sand alone and also mixed with rubber chips and granulated rubber are presented. Results of relative density tests demonstrated that the optimum rubber mixing ratio of 30% in weight acquires the least void ratio when sand is mixed with rubber chips. The sand alone tests resulted in an effective strength envelope which is approximately linear with a friction angle of approximately 36.8° in both stress paths. While, the outcome of the two different loading methods on the sand-rubber mixtures is an approximately bilinear stress envelope. The internal friction angle of sand mixed with rubber chips is greater than that of sand alone by 8.5 and 4 degrees under the CAS and CRS conditions, respectively. This parameter is about 1.5 and 5 degrees less than sand alone for granulated rubber mixed with sand, under the CAS and CRS conditions, respectively.