E – 1400 Scrap Tire Earth Retaining Structures

Throughout the United States and Canada, millions of waste tires are generated each year. Huge stockpiles of waste tires represent an enormous depot of lost energy, materials, and money. Moreover, waste tires present a number of environmental, health and safety hazards to the public and represent a serious public nuisance. While scrap tires represent only about 2 percent of the total solid waste stream in industrialized countries, tires decompose slowly. This combined with limited uses of scrap tires and limited methods of disposal results in stockpiling of scrap tires. According to the Rubber Tire Manufacturer Association, US annual tire production is about 270 million and Canadian annual tire production is about 25 million. US scrap tire stockpiles are estimated to be about 700 to 800 million tires, with 17 US states having individual stockpiles with at least 1 million scrap tires. The US EPA estimates that 9 million scrap tires are exported annually from the US. Most of the exported tires go to undeveloped countries for further use on vehicles and eventually into stockpiles.

This course outlines three uses of scrap tires as earth retaining structures. Included are example designs of retaining walls that utilize the following types of products as the basic structural unit: (a) individual tires filled with gravel or low strength flowable fill, (b) bales of compressed tires, (c) compressed tire bales encapsulated in reinforced concrete. The design charts have been developed for varying wall heights and batter, as well as for various loading conditions.

This course is based on the publication, “Use of Whole Tires in Earth Retaining Structures” by the Texas DOT, US DOT, FHWA and The Center for Multidisciplinary Research in Transportation at Texas Tech University. The techniques and methodologies described in this course document are evolving rapidly.

With the increasing number of scrap tires in the US and Canada, the problem of scrap tire disposal will only grow. Regulated stockpiles and illegal dumps pose major environmental and safety problems, such as combustibility and possible toxins in the leachate. They also provide habitat for insects such as mosquitoes. Mechanically stabilized earth and gravity walls can be an effective use of large quantities of scrap tires. Scrap tire earth retaining structures appear to be economically competitive and no harder to construct than conventional walls. While the exact costs of all types are unknown, the assumption can easily made that the scrap tire walls will be cheaper.