California Demonstrates New Use For TDA

First of its kind project uses tire-derived-aggregate fill for mechanically stabilized earth retaining wall

In California’s Santa Barbara County, Ortega Ridge Road had been slowly failing for over a decade.  Recurring settlement of the roadway surface and embankment required constant maintenance, county engineers and public works officials said.

The road was constructed in the late 1960s with clay shale. When it rains, the clay absorbs the water and expands. As the weather dries out, this clay shrinks and causes the road to crack and fail.

Every few years, the road would settle to the point that it required county maintenance crews to install a pavement overlay to maintain the profile.  In 2015, the extent of road settlement forced county engineers to realign the road and close it down to one lane of alternating traffic. It remained the sole access to Toro Canyon for several years until road and bridge work on nearby State Route 192 was repaired or replaced. After their completion the county was able to close the road and construct the project. In coordination with CalRecycle, a pilot project to reconstruct the road with the tire derived aggregate (TDA) produced from scrap vehicle tires was funded and public works officials received the technical know-how to develop and construct the project.

In 2019, Santa Barbara County Public Works Department completed the Ortega Ridge Road Slide Repair MS-TDA Wall Project which uses tire-derived aggregate (TDA) as lightweight fill material to prevent the ground under the road from slipping.

This pilot project, a partnership between CalRecycle and the County, is the first in the state to combine the use of TDA and a mechanically stabilized earth retaining wall (MSE wall). The TDA is separated from the earth in a way that strengthens the ground and helps to prevent it from moving and the MSE wall is created with stone-filled wire baskets that stabilize the road.

More than 30 inches of asphalt had been placed on the roadway over the years in attempts to fix the road. Officials said a traditional, long-term repair solution was expected to be costly and challenging, as a conventional project would require the acquisition of an additional easement for construction. The 28-foot deep failed embankment and utilities within the embankment presented a challenge for construction crews.

In addition, the site is located in a coastal zone, where permitting large retaining structures is costly and time consuming. The  TDA lightweight fill reduced the need for a large footprint, while also eliminating the need for a retaining wall and permitting requirements.  The California State Association of Counties praised the project for its streamlined design and construction, reduced environmental impacts, smaller construction footprint and cost savings.

UC San Diego conducted research on the road repair techniques, which provided the engineering data for the project design. Researchers determined that TDA is seismically safe for a retaining wall and road repairs and it will not degrade due to poor underlying soils or saturated conditions.

Santa Barbara County was awarded the top honor in the 2020 Outstanding Local Streets and Roads Project Awards. The county was recognized for innovations in sustainability with the Ortega Ridge Mechanically Stabilized Tire Aggregate Wall, in which the reconstruction of the 225-foot section of roadway diverted 81,000 tires from the state’s landfills in the form of tire-derived aggregate fill.

Funding for the $665,000 construction project was provided by CalRecycle TDA grant funding ($110,000), TDA pilot project funding ($330,000), the county’s general fund ($43,000), and the State Transportation SB1 Fund ($182,000). Additional construction engineering costs were reimbursed by CalRecycle’s TDA grant funding in the amount of $36,000. The project was constructed by Raminha Construction and the roadway was officially reopened in August of 2019.

“This CalRecycle grant project is a new model for how communities can transform recycled waste tires into a valuable resource to improve local infrastructure and protect public safety,” CalRecycle officials said. “This has been a collective effort with the cooperation of Santa Barbara County to be part of this first-of-its-kind project. We hope this is the first of many statewide projects that will make use of this new civil engineering technique.”

Santa Barbara public works officials also gave thumbs up to the project saying it gave them departmental support to venture out away from past tried and true techniques to go for something different. This program’s success means Santa Barbara can solve more problems with these new materials and techniques in future projects.

© Scrap Tire News, August 2021