TIRE CHIPS AS LIGHTWEIGHT BACKFILL FOR RETAINING WALLS - PHASE II

Waste tires cut into 25 to 305-mm (1 to 12-in.) pieces yield a material that is coarse grained, free draining, and has a low unit weight, thus offering significant advantages for use as retaining wall backfill. This project is a continuation of Phase I, in which the engineering properties of tire shreds were determined. The purpose of this project was to determine design criteria for using tire shreds as retaining wall backfill. This was done by testing a granular control fill and tire shreds from three suppliers in a full scale retaining wall test facility. Tests were performed for at-rest and active conditions. For the at-rest condition, the horizontal earth pressure, interface shear, and compressibility were measured, at surcharges up to 35.9 kPa (750 psf). As much as 7% strain occurred during surcharge application with an additional 3% occurring due to time-dependent settlement. The majority of time-dependent settlement was completed in 50 days. For the active condition, the horizontal earth pressure and deformation within the backfill were measured; tests were performed at the 35.9 kPa (750 psf) surcharge. The horizontal earth pressure for tire shreds was 35% to 45% less than expected from conventional granular fill. The coefficients of lateral earth pressure (K sub 0 and K sub a) were found. K sub 0 for tire shreds decreased with depth and fell within a small range. At the maximum surcharge and a depth of 2 m (6.5 ft), K sub 0 ranged from 0.32 to 0.33. K sub a for tire shreds was constant with depth and fell within a small range. At 0.01H of outward wall movement, K sub a ranged from 0.22 to 0.25. The interface shear strength between tire shreds and a concrete faced wall ranged from 30 deg to 32 deg.