NOTATION AR Aspect ratio a 0 …..a 3 Coefficient of the regression equations for each response variable evaluated CC Chip content c’ Cohesion EAC Energy absorption capacity E i Initial stiffness φ’ Friction angle σ 3 Confining pressure (σ 1 – σ 3 ) f Deviator stress at failure x 1 ….x 3 Input variables y Response variable 1. INTRODUCTION Complete recycling of scrap tires is difficult as they contain integrally combined tread rubber, steel wires and synthetic fibers. Shredding is the only means for easy disposal. The product of shredding is referred as to “Tire chips” when they are generally between 12 mm to 50 mm in size. The term “Tire shreds” is used when particles are larger (Lee et al 1999). The specific gravity of the tire shreds/chips varies from 1.02 to 1.26 Ahmed, 1993; Edil and Bosscher, 1994 and Foose et al, 1996) depending upon the quantity of steel belting present. Bosscher et al. (1993) reported that shred- ded tires do not show any likelihood of being a hazardous waste. The tire leach data indicate little or no likeli-hood of shredded tires having adverse effects on ground water qual- ity. Bosscher et al (1997) concluded that chips smaller than 75 mm are easy to handle. The problems with the use of pure tire shred / chips are that of spontaneous combustion. However, such is unlikely in tire chip-soil mixtures due to non-availability of adequate oxygen (Venka-tappa Rao and Dutta, 2006). Ahmed (1993) conducted triaxial tests on the mixtures of tire chips with Ottawa sand and Crossby Till. He found that the apparent cohesion in-creases and friction angle decreases as the chip content is increased in the mix. Edil and Bosscher (1994) reveal that addition of 25 % chips (size 20 to 80 mm) to sand results in shear strength (obtained by direct shear test) slightly greater than that of dense sand at low normal stresses. At higher normal stresses (76 kPa) the effect of tire chips on shear strength was not as dramatic irrespective of the tire chips content. The studies conducted by Foose et al (1996) on sand reinforced with shredded waste tires of sizes 6 to 50 mm (designated as 50 mm shred), 50 to 100 mm (designated as 100 mm shred) and 100 to 150 mm shred (designated as150 mm shred) in a direct shear test, reveal that the Mohr strength envelopes were non-linear and were influenced by shred contents; normal stress and sand matrix unit weight, and opined that shred length may have only “border-line significance”. Lee et al. (1999) determined the stress-strain relationship of mixture of sand and tire chips and observed that the dilatancy behaviour of rubber sand is in be-tween pure sand and pure chips. This type of R. K. Dutta 1* and G. Venkatappa Rao 2 Regression models for predicting the behaviour of sand mixed with tire chips ABSTRACT: The paper presents the behaviour of sand mixed with tire chips. For this purpose drained triaxial compression tests with strain measurement were conducted on sand mixed with tire chips. The joint effects of chip content (up to 20 %), aspect ratio (up to 2) and con-fining pressure (up to 276 kPa) on the behaviour of sand using multiple regression analysis were investigated. These empirical models may be useful for preliminary esti-mation of energy absorption capacity, deviator stress, initial stiffness and cohesion and friction angle of sand mixed with tire chips. KEYWORDS: Energy absorption capacity; Deviator stress; Initial stiffness; Cohesion; Friction angle: Regression model. *Corresponding Author 1 Department of Civil Engineering, National Institute of Technology, Hamirpur – 177005, India, Email: rkd@nitham.ac.in, Phone No.: +91-1972-254330(O). 2 Honorary Professor, Department of Civil Engineering, University College of Engineering, Osmania University, Hyderabad - 500 007, A.P. India, email: gvrao.19@gmail.com, Phone: +91-9908383330. 51 International Journal of Geotechnical Engineering (2009) 3: (51-63) DOI 10.3328/IJGE.2009.03.01.51-63 J. Ross Publishing, Inc. © 2009