California, September 28: Engineers in California used hundreds of thousands of shredded waste tyres as lightweight construction material beneath a highway on-ramp turning a major waste management challenge into an infrastructure solution.
The project was carried out in 2000 at the Interstate 880 and Dixon Landing Road interchange in Milpitas, where engineers faced around 30 feet of soft, unstable bay mud. The planned southbound connecting ramp required an embankment about 26 feet high 700 feet long and 50 feet wide.
Using conventional soil or rock would have placed substantial weight on the weak foundation and could have resulted in long term settlement. Engineers therefore used tyre derived aggregate made by shredding discarded vehicle tyres as lightweight fill.
About 662,700 shredded tyres weighing roughly 6,627 tons were used in the foundation. According to CalRecycle project records cited in the report the material reduced the downward pressure on the underlying soil by around 40%.
A conventional earth embankment would have exerted approximately 3,750 pounds per square foot of pressure on the foundation. The tyre derived aggregate reduced this to about 2,250 pounds per square foot.
The approach also produced financial savings. CalRecycle reported that the use of shredded tyres instead of commercial lightweight aggregate saved approximately $477,000 in project costs.
The tyres were installed in two layers, each up to 10 feet thick with a three foot layer of low permeability soil separating them. Geotextile fabric was also placed around the sides to prevent surrounding soil from entering the spaces between the rubber pieces.
The project addressed another environmental problem facing California at the time. The state was generating millions of discarded tyres annually while large uncontrolled tyre piles posed fire and pollution risks.
More than two decades after the project was completed, CalRecycle records cited in the report indicate that the on ramp continued to operate without reported structural or maintenance problems.
The project subsequently became an example of how tyre derived aggregate can be used in civil engineering including for stabilising slopes, filling behind retaining walls and reducing the weight placed on weak soils.
The Milpitas project demonstrated that processed waste tyres can serve a structural purpose when appropriately engineered while also providing a potential use for a difficult to manage waste material.