Tire derived aggregate (TDA) is used for a wide range of public works projects and other civil engineering applications. These include lightweight embankment fill, landslide repair/slope stabilization, various landfill applications, retaining wall backfill, vibration mitigation, and more.
Lightweight Embankment Fill
When constructing soil fills on unconsolidated sediments the additional force from the weight of the fill on the underlying material may result in settlement over time. This consolidation can cause substantial engineering challenges and must be considered during the design.
Differential settlement can occur as the roadway transitions to a stationary surface, such as a bridge abutment, creating a bump in the road surface. These areas require extra maintenance to avoid creating an unsafe condition. Tire-derived aggregate (TDA) can be used to limit settling by decreasing the weight of the fill, resulting in a significant advantage to engineers in both cost and construction of the project.
In 2000, an embankment fill was constructed for the Dixon Landing Road/Interstate 880 south bound on-ramp in Milpitas, California. This completed project resulted in an overall project cost savings by using TDA as the lightweight fill material, and by shortening the project timeline by decreasing the surcharge and consolidation time that was required. When lightweight construction fill is needed, TDA can be the cost-effective solution.
Landslide Repair/Slope Stabilization
When a road landslide or "slip out" occurs, it is often necessary to excavate the sliding road material down to more stable soil and then rebuild the slope and road in compacted layers of soil called lifts. Drainage networks are typically installed so that hydrostatic pressure does not build up behind the fill, causing potential instability. By using TDA as a lightweight backfill material, less excavation is necessary and TDA’s free-draining properties allow for a more cost effective design.
In 2007 the California Integrated Waste Management Board (CIWMB), now the Department of Resources Recycling and Recovery, or CalRecycle teamed with the Mendocino County Department of Transportation to develop an alternative method for landslide repair using TDA. The solution involved using TDA in a section of Marina Drive near the city of Ukiah which had been damaged by a landslide. This project used 131,000 tires. CIWMB later partnered with Sonoma County Public Works Department to repair two similar road slide projects at Geysers Road and Sonoma Mountain Road.
TDA can be used as drainage material in landfill gas and leachate collection and removal systems. Both Type A and Type B TDA can be used as a gravel substitute in these applications. Throughout California, TDA is being used as a cost-effective substitute for gravel in landfill gas collection trenches, header pipe protection and leachate recirculation systems.
Retaining Wall Backfill
TDA is a good backfill material to use when designing a retaining
wall because it is lighter than soil, is free draining, and has a
high internal angle of friction, which results in significant
pressure reduction on the wall.
The weight of TDA is about two-thirds that of conventional soil and combined with the free draining property of TDA, the pressure against the retaining wall is significantly reduced.
The benefit of this is that the materials used to construct the retaining wall can be reduced, therefore reducing the cost of construction, which can result in substantial savings.
Through an interagency agreement between CIWMB and Caltrans, two pilot projects in Riverside County were constructed using TDA backfill behind standard Type 1 retaining walls. The walls were fully instrumented to analyze the effects that lightweight TDA backfill had on reducing the soil pressure on the walls.
Prior to construction of the Vasona Light Rail Line, the Valley Transit Authority (VTA) in San Jose, California, sought to find an effective, cost-saving alternative to using conventional vibration mitigation technology. This technology consisted of rubber ballast mats, special track fasteners, or floating concrete slabs to mitigate ground vibration. It was effective but expensive to install. This was a joint effort between CIWMB and the VTA.
In 1999 CIWMB conducted a large scale field test to examine the effectiveness of TDA to mitigated vibration. With the findings obtained from that study, the VTA constructed a, 80-foot-long test section in their San Jose rail yard. The result from the two studies indicated that TDA was a cost effective vibration mitigation alternative to the conventional technology currently used by VTA.
The goal in using TDA was to reduce the ground-borne vibrations that affect residences and business located adjacent to the transit lines. Based on the favorable results in the VTA maintenance yard, the VTA decided to use TDA as a vibration mitigation method for the Vasona Corridor Light Rail Extension Project.