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Stabilizing the bluff
By Jeremy Joseph
The Briarcliff City Apartments sit high on a bluff in Kansas City, Mo. The master-planned community offers residents fine views of downtown and the Missouri River valley. Apartment dwellers enjoy restaurants, shops, and trails located within walking distance of the residential apartment complex.
But the bluff that made the community appealing also put it at risk of even getting built. Part of the bluff that would support the complex’s parking lot and swimming pool was eroding and a special retaining wall was needed to structurally support it.
Retaining wall installer, Randy Grego, said: “It was important for us to take on this project. The Briarcliff apartment community is significant not only to the people who live there, but to many others who enjoy the views, shops, and restaurants the community has to offer.”
Engineering assistance
The project wasn’t going to be easy. Work crews faced logistical issues. There was no access from the front and not much space in the back of the bluff area to store materials. Because of the lack of storage, workers had to bring materials in as needed. In addition to the logistical challenges, an unusual amount of rainfall resulted in erosion behind the wall during its construction.
“This was a challenging project on many levels,” said Grego. “In addition to logistical issues, the cut at the back of the reinforced zone was unstable and intermittent sliding had occurred.”
Mike Stein, P.E., was brought in as the project’s engineer and wall designer. He pointed out another dilemma: The upper portion and lower portion of the wall were on different limestone rock formations. Stein also noted that the area had been a borrow-and-dump site, requiring removal of a mixture of shale materials and soil in the excavation area.
Offering a different solution
Originally, a wall incorporating a polyester geogrid had been specified. However, the environmentally conscious owner/developer wanted to use recycled concrete within the reinforced zone, a type of backfill material typically not allowed in retaining walls utilizing polyester geogrids.
The contractor made some inquiries and eventually specified a wall system that incorporated polyethylene, noncorrosive geogrids for reinforcement, with the capability to withstand the concrete’s alkalinity. The uniaxial geogrids are made from high-density polyethylene and are resistant to physical deterioration and loss of strength caused by aggressive chemical environments. The inert properties of the geogrids permit the use of a wide range of backfills, including recycled concrete.
“This system was the right solution for the Briarcliff project because of its proven track record,” said Grego. “[It] provided us with the right materials to make sure the wall was not only structurally sound, but also attractive.”
Building around access challenges
To overcome the access issues, the retaining wall was built from the top of the bluff down. Since there was no access to the front of the site due to the steepness of the bluff, the retaining wall was actually backfilled from the top of the bluff. Twenty thousand tons of recycled concrete were purchased and brought to the site.
The contractor set up a conveyor station at the top of the bluff to position the aggregate behind the wall. The aggregate was loaded onto the belt and dropped into the reinforced zone. Construction loaders then spread the backfill.
A 4in.-thick concrete leveling pad was poured at the foot of the wall, and retaining wall units in a blend of almond, buff, and gray colors were placed. The color variation gives the wall a vivid look and feel that complement the surrounding complex. Twelve vertical piers (see background in Photo 2) within the reinforced zone were installed in sections at the top of the bluff to support the residential development as the project was being completed.
Once the retaining wall was installed and construction of the complex completed, the apartment community flourished.