In 2011 Texas drove recycled plastic made from discarded bottles into a failing US 287 slope; 5 years later, settlement was minimal and costs were 50 percent to 80 percent lower

Along a highway slope beside US 287 in Midlothian, Texas, engineers faced a problem that had become familiar on many roads built over unstable clay soils. Cracks formed close to the side of the highway, and the soil below started shifting slowly. Instead of using traditional large structures to rebuild the hillside, researchers decided to test an unusual technique of stabilization using specially reinforced pins made from recycled plastic.

In 2011, the Texas Department of Transportation made an experiment that involved implementing technology of using recycled plastic pins at the troubled site near the St. Paul overpass. The experiment was designed to see whether discarded plastic materials could provide enough strength to stabilize highway embankments. The Transportation Research Board reported that 5 years of monitoring showed minimal settlement after installation, while cost analysis indicated the method could reduce stabilization expenses by 50 percent to 80 percent compared with conventional approaches.

A highway slope problem caused by moving soil


The US 287 slope failure was not a failure from a sudden collapse. Rather, the problem developed gradually as soil beneath the highway shifted over time. The area was constructed on very plastic clay which expands and contracts due to changes in moisture content. Over time, these movements developed cracks near the bridge approach, and posed a threat to the stability of the highway embankment. A University of Texas at Arlington research team said in a study that it chose the location to test whether recycled plastic pins could reinforce the slope without large retaining structures. The idea was simple: drive strong recycled plastic members deep into the slope so they could resist movement along the shallow failure surface.

How waste plastic became a tool for road repair

The recycled plastic pins were not ordinary pieces of plastic. They were manufactured mainly from recycled plastics. They were intended to be used as reinforcing components within the soil. Three sections of the US 287 slope, each about 50 feet long, were reinforced with the pins. Two similar, untreated sections were also left to see how they fared over time as well. Once installed, equipment such as inclinometers and surveying instruments was set up around the slope to monitor movement. This was not only to determine if the slope survived but to quantify by how much the slope had shifted.

What 5 years of testing revealed

The comparison between the reinforced and unreinforced sections showed the impact of recycled plastic pins. Settlement in the untreated control areas was as high as 15 inches at the top of the slope. Further movement continued throughout the monitoring period, confirming that the slope remained unstable until it was reinforced. The reinforced sections exhibited different behavior. Only about 2 to 4 inches of total settlement were recorded, much lower than the untreated sections, and additional settlement after installation was minimal. Horizontal movement also decreased significantly after one year, with one reinforced section showing less than 0.1 inch of additional movement. The results indicated that recycled plastic pins may be adequate to support shallow slope failures in problematic clay soils.

The future of plastic reinforcement

The US 287 experiment offered engineers long-term field data about how recycled plastic reinforcement behaved under real weather conditions. Following the Texas project, engineers examined recycled plastic pins for other transportation challenges, including additional highway slopes and bridge-related applications. Further studies focused on improving installation techniques, identifying suitable locations for the technology, and evaluating how recycled materials could be used safely in infrastructure projects.