Public art plays an integral part of the landscape design for a unique road-widening project along 1st Avenue in Tucson, Ariz. In contrast to the usual stone or metal decorative art, this unique concept is both artistic and functional, with bas-relief sculptured retaining walls serving as huge pieces of public art, funded by one percent of the total project cost.

Landscape Architect Paul Edwards won the project after responding to a call for artists administered by the Tucson-Pima Arts Council. Edwards' detailed design incorporated textures, colors and forms inspired by the surrounding geological formations. The top edges of the walls are sculpted to reflect the visible mountains in the landscape of the southwest desert.

Edwards used common construction materials in an innovative way. He incorporated art into the necessary functional infrastructure elements, such as retaining walls and sound walls. Also key to the design was a unique way of maximizing the impact of art while working with narrow right-of-way acquisitions.

Next, Edwards’ unique design was brought to life with an art rock cladding, incorporating all county technical and structural requirements. A detailed one-foot grid was drawn on the wall from the art plan. Artisans accomplished the initial shaping of the wall cladding by bending a rebar armature to exactly match the drawings in the construction documents.

Project Manager J.R. Cook of The Larson Company, who built the wall, describes the process: "Our job was to accomplish the artist’s vision and bring his rendering to life in a timely fashion," said Cook. "The actual structural portion was a cast-in-place concrete wall with a footing just like any other retaining wall. We added a rebar reinforcing structure, shot the rebar with concrete and then carved that concrete to resemble the shapes -- the mountains, the sky, the stars, etc. Then we painted it with the approved colors."

A shotcrete structure coat was applied to the armature and hard-carved to define the shape. Equipment used to place the shotcrete included a Putzmeister model Thom-Katt 2040 trailer pump and an Ingersoll Rand portable compressor. Hand tools were used to help create the shapes, including 4-foot plasters Darby, plasters hand trowels and some tools that were custom made by Larson to create impressions. To give the art better definition through shadow patterns, the lines were sculpted up to three inches in depth.

The project began with a simple, cast-in-place (CIP) concrete wall, which was later covered in shotcrete and manipulated by hand-carving. Many such walls are now being built entirely of shotcrete, without use of CIP walls.

A waterproof shotcrete integral color coat was applied. A muted, desert-hued, paint coat was then hand-applied using an airless paint sprayer, along with Hudson sprayers and spritzer bottles.

"There are four different sections to the wall," said Cook. "The longest section is about 180’ long and about 15’ high. There are shorter sections, some of which are probably 60’ to 70’ long and only 3’ or 4’ tall. The big one was a challenge in terms of the approach -- we worked from the top down. The landscapers were the last people in, after we completed our work. That’s when the final grade was done and the landscaping was completed at the base of these walls, and above them."

The planting design by Landscape Architects Paul Wichmann and Rick Schonfled, solved the problem of very limited spaces along most of the right-of-way and the limited opportunities for median plantings. On those medians where planting was possible, sight visibility requirements constrained the use of trees and larger plants.

A shotcrete structure coat was applied to the armature and hard-carved to define the shape. Equipment used to place the shotcrete included a Putzmeister model Thom-Katt 2040 trailer pump and an Ingersoll Rand portable compressor.

The design features a desert approach using native and non-native arid lenad plants. Desert trees and larger shrubs are used to soften and buffer the screen walls and retaining walls. With the use of desert-adapted plant materials, the intent was to provide visual interest for motorists and pedestrians with a variety of foliage textures, colors and branch structures.

Flowering plants provide bold accents at junctures and high-visibility areas such as median ends and corners. Vines and smaller plantings soften the base of walls where there was limited planting space. To retain the desert characteristics, native hydroseeding and container-grown native trees are used on the cut and fill slopes that drop away from the roadway. Plant material selection and installation was supervised by the Pima County Department of Transportation.

Once the basic outlines of the artist’s design were sculpted, the textured surface was created with form liners placed horizontally to simulate exposed bedrock. Mock-ups were created with an integrally colored finish coat of shotcrete.

Originally, the existing two-mile corridor, a major urban arterial, was a three-lane road carrying approximately 29,000 vehicles daily. To handle projected traffic volumes of up to 41,000 vehicles, the corridor was designed to a four-lane divided urban standard. Neighborhoods played an active role through their Citizens Advisory Committee representation in ensuring compatibility with land uses while accommodating the needs of the general traveling public. Mitigation measures include the use of noise walls, dense arid parkway and median landscaping, and optimal placement of median openings for access.

The role of public art in landscape design continues to evolve. On this project, it proves its worth by making the street more attractive, identifying the neighborhood and increasing the livability of the community.

The "Art Rock Wall:"

Creating Functional Beauty with Shotcrete

The periodic location of the sculpted walls along this two-mile project helps avoid the appearance of corridor or tunnel walls. The sculpted wall tops reflect the shapes of the nearby mountains.

Tucson’s public art retaining wall project represents a growing trend among wall designers: the concept of the "art rock wall." This type of wall serves not only a practical retaining purpose, but offers beautiful art designs, usually sculpted through the creative use of shotcrete. Some of these walls are even being constructed entirely of shotcrete without a cast-in-place concrete base.

J.R. Cook, project manager for The Larson Company spoke with LCM about this growing trend, as exemplified by an art rock wall currently under construction at a residential project in Vail, Colo.

The completed project features desert-adapted plant materials to provide visual interest for motorists and pedestrians with a variety of foliage textures, colors and branch structures.

"The Tucson wall uses shotcrete as an artistic covering for a cast-in-place wall," said Cook. "We’re doing a project at a private residence in Vail, Colo., right now that is about two-thirds done. Instead of a cast-in-place wall, we did a soil-pinning exercise and are covering that with shotcrete. It’s a driveway that’s a couple hundred feet long, incorporating three tiers of retainage and some steps."

Cook points out several advantages of using shotcrete instead of cast-in-place concrete. "In an area such as a highway right-of-way or a real sensitive residential area, you can cut out only what you need to cut out, and the dirt is essentially the form on the back side," he said. "The shotcrete doesn’t require forming on the front side because it’s mixed in a consistency that makes it stick. And it’s much less intrusive to the environment because you don’t have to over-excavate and backfill. You only have to excavate to the point of your cut, and then stabilize it."

This residential retaining wall in Vail, Colo., uses a soil-nailed shotcrete wall as its base instead of a cast-in-place wall. Cook says this method is not only less expensive, but also less intrusive to the environment. "You can cut out (inset) only what you need to cut out, and the dirt is essentially the form on the back side," says Cook. "The shotcrete doesn’t require forming on the front side because it’s mixed in a consistency that makes it stick."

In addition, using shotcrete to create this type of wall is less expensive, and doesn’t require form work, according to Cook. "It’s getting to be a more and more common technology on cuts in highways, in places where they want to stabilize the cut but also make it more interesting visually."