Use of Shredded Tires as Lightweight Backfill Material for Retaining Structures

Abstract

Each year in the United States, approximately 242 million automobile, truck and specialty tires are discarded. Almost 78% of these scrap tires wind up in overcrowded landfills, and thousands more are strewn across the country's empty lots, highways and illegal tire dumps. Used tires pose both a serious public health and an environmental threat. Therefore, economically feasible alternatives for scrap tire disposal must be found. Some of the current uses of scrap tires are tire-derived fuel, barrier reefs, and crumb rubber as an asphalt additive. However, all of the recycling, re-use and recovery practices combined only consume about 22% of the discarded tires. Thus, a need still exists for the development of additional uses for scrap tires. This paper addresses one potential use of scrap tires within the civil engineering field. Specifically, the feasibility of using shredded tires as a lightweight backfill material for retaining walls has been investigated. In this study, laboratory tests were first performed to determine the engineering properties of shredded tires. Based on sieve analyses, the shredded tires used for this study can be classified as uniformly graded material. The unit weight of shredded tires was found to range from 35 to 38 lbs ft-3 (pcf), and the hydraulic conductivity was determined to be 0.03 cm s-1. The values of shear strength parameters, cohesion and angle of internal friction, were determined to be 147 lbs ft-2 (psf) and 27 degrees, respectively. Using these properties, retaining walls of various heights were then designed using shredded tires as the backfill material. Retaining walls were also designed using conventional sand as the backfill material for comparison purposes. When comparing the overall cost for the retaining wall using shredded tires with the retaining wall using sand, a substantial cost saving was realised by the use of shredded tires. An increase in the factor of safety was also a result of using shredded tires instead of sand as backfill. The results of this study indicate that shredded tires have a definite potential to be used as a backfill material for retaining structures.