Tire Chips as Lightweight Subgrade Fill and Retaining Wall Backfill Author(s): Humphrey, Dana N. & Sanford, Thomas C. Origin: Maine Date: October, 1993 Categories: Performance Key Words: Tire chips, scrap tires Summary: Scrap tires that have been cut into chips are coarse grained, free draining, and have a low compacted density, thus offering significant advantages for use a lightweight subgrade fill and retaining wall backfill. This paper presents the engineering properties that are needed use tire chips for these purposes. The following properties were determined for tire chips from three suppliers: gradation, specific gravity, compacted density, shear strength, compressibility, coefficient of lateral earth pressure at rest, and permeability. For most of these properties tests were also performed on tire chips from a fourth supplier. The maximum size of the tire chips tested was 76 mm (3in.). This large size, in combination with the high compressibility of the tire chips, made it necessary to design and fabricate custom testing equipment.