Structural Soil and Permeable Paving at UT-Austin

Location: Austin, Texas
Owner: University of Texas
Landscape Architect: Peter Walker & Partners
Contractor: Flintco Construction
The Story: Expanded Shale Utilized in Structural Soil Media on UT Campus

College campuses across the United States are constantly under change adapting to the growth and educational demands of students. It is often a tough balancing act. The Speedway Mall project at the University of Texas is a $36 million dollar project to transform a vehicular street into a 36’ wide pedestrian mall that encourages safety, social interaction, preservation and green infrastructure.

The campus master plan identified several goals. Foremost was to reduce vehicular traffic while balancing the needs of pedestrians, cyclists and service vehicles. It also strived to improve the character of the Speedway by incorporating the established oak trees into a more human-scaled design. The plan would develop spaces for students to gather informally, where campus wide activities would occur, such as festivals, student organization gatherings and musical performances. The final design encompassed close to nine acres and was completed by the prestigious landscape architectural firm of Peter Walker & Partners from Berkeley, California.

Flintco Construction was the general contractor at Speedway. The project scope involved minor grade changes along the former roadway, minor utility upgrades, lighting and power improvements, construction of a plaza at Speedway’s intersection with 24th Street, food truck parking and landscape enhancements. Preserving the mature oak trees was vital to maintaining the character of the UT campus. There was also a push to transition away from impervious concrete and asphalt toward more green solutions such as permeable brick paving.

A structural soil was specified by Peter Walker & Partners that utilized expanded shale. The soil media contained 80% expanded shale and a 20% topsoil/sand mix with organic matter. It was placed at a 24” depth. The soil component provides a fertile growing medium in the voids between the aggregates, retaining moisture and nutrients for vigorous long-term plant root growth. The lightly compacted structural soil supports the permeable brick paving system and extends from the base of the tree to the limits of the permeable brick paving. The porous nature of the structural soil is helpful in mitigating the grade changes around the oak trees and aids in balancing the oxygen and water requirements at the root zone. Expanded shale also helps to improve the clay soil conditions where the new trees and landscape plantings were designed. PWP has used expanded shale on other Texas projects including the Nasher Sculpture Center, the University of Texas at Dallas, and the UT Southwestern Medical Center’s William P. Clements Jr. University Hospital.

Phase 2 of the Speedway Mall project is scheduled for completion in 2018.