Limestone in Austin
When choosing retaining wall materials, several factors should be considered. Matching the color and texture of the retaining wall materials to what’s naturally found in the area helps integrate the wall into the geography. Retaining wall materials that blend in with the local environment look more natural and enhance community aesthetic value.
Natural limestone is prevalent underneath Austin, TX. Its durability and beauty have made this type of rock a frequent choice for local building projects. When officials at the Texas School for the Deaf, located on the edge of downtown Austin, considered replacing a cast-in-place concrete wall that was eroding, they thought about using limestone for the new wall.
However, they ended up choosing straight-faced Keystone Compac Units from Keystone Retaining Wall Systems of Minneapolis, MN. This product gives the appearance of limestone, but offers advantages over limestone.
It is “less expensive and stronger than the actual stone. Many people who see the wall assume it is limestone,” says Aaron McMillan of Jewell Concrete Products, a licensed Keystone supplier.
The Keystone Compac unit has an open-core design. Lighter in weight than other structural blocks, its shortened tail design makes it easier to handle and ideal for projects that do not require the embedment length of the Keystone Standard unit.
The Keystone Compac is available in the traditional sculptured/tri-planar and straight-face styles and also in a hewnstone face style. Customers can choose from a variety of weather finish options.
Texas School for the Deaf is near the Texas State Capital. Its attractive wall parallels a main thoroughfare, Congress Avenue. The Keystone design allowed the contractor to move the existing slope far enough back from the street to create a wide pedestrian walkway.
Architect Carl Gromatzky of Barnes Gromatzky Kosarek Architects in Austin designed the wall. His firm has designed various buildings at the school. Completed in 2004, the wall took 10 months to construct.
Pedestrians pass by the tree planters at the base of the wall, which have top edges wide enough to sit on, if desired. The school’s name surrounding a Texas star emblazons the wall in brass letters. At the top of the wall—visible from street level—a straightforward wrought iron fence and live oak trees that were carefully preserved form a clear boundary of the 67-acre campus.
The wall is 15 feet high. For the urban setting, the architect used “new trees at street level, vines, and seat wall planters [to] diminish the overall scale of the wall.”
Gromatzky’s innovative approach—what he describes as “simply using the product in a different way”—resulted in diminishing the scale of the wall. His design, while completely meeting the functional requirements of the site, offers the respite of nature and good aesthetics to urban pedestrians and motorists alike.
Gromatzky says that the 900-foot-long wall is a serpentine one for two reasons. The undulating form is more interesting to look at than such a large plain form—the wall measures 10,000 square feet—would have been.
The serpentine wall design also creates space for more than 20 right-angled tree planters along the bottom of the wall as it joins the sidewalk. Getting the planters properly aligned was a bit tricky, but it all fit together perfectly. Gromatzky notes that “the serpentine shape allowed us to plant new trees at street level and allowed us to maintain a generous sidewalk width.”
He says that one of the project’s challenges was having to make excavation cuts as large as 15 vertical feet, working in a confined area. Workers had to be sure that existing live oak trees were not damaged.
Keystone Compac was uses a pin connection system. Workers made a series of saw cuts near the top of the wall to follow the tight contours of the design.
Gromatzky cites the Keystone system’s flexibility for making it possible to install the wall and still preserve the large live oak trees on the property. “We did not need large footings that could have damaged the root systems of the large oak trees on the high side of the wall.”
Other challenges within the project were presented by existing limestone deposits and unanticipated drainage problems. The original plan for placing the trees along the wall had to be adjusted.
Inadequate drainage after the sidewalk installation was corrected by drilling cores through the limestone. Doing this allowed the trees’ roots to drain sufficiently.
Working in a busy urban area can be a logistics nightmare, trying to coordinate workers and deliveries of materials. Closing traffic lanes to have room for a staging area adds to the difficulty. McMillan says that Jewell Concrete Products employees worked hard to be sure the right materials were on hand as needed and readily accessible by the wall construction crew.
The wall project was further complicated by the number of different entities involved. Gromatzky notes that it required coordination between the Texas School for the Deaf (the state of Texas) and the city of Austin to accomplish the work in the right of way.
He says, “The Texas School for the Deaf was our client and paid for the wall. The city of Austin’s Utility Department (Austin Energy) paid for the new trees through a program to mitigate urban heat island effect.”
