West Chester Township, just outside of Cincinnati, OH, has seen tremendous growth as the Cincinnati-Dayton metropolitan areas continue to converge.
Until recently, West Chester did not have a downtown to speak of. Developers started brainstorming a planned downtown area, and West Chester’s new Towne Center was born. Towne Center includes several mixed use developments and the new West Chester Township Library. The $16 million development encompasses three buildings and 115,000 square feet of space with the architecture meant to have a classic small-town feel.
The Square at Union Centre is designed to be the central gathering place for the township with a 2-acre park and open space for concerts and other events. The square overlooks a pond that catches stormwater runoff from the other areas of Towne Center, creating a functional, yet attractive, focal point for the development. The square features a prominent green clock tower and matching pedestrian bridge. The installation of the 57-foot-long by 8-foot-wide pedestrian truss bridge drew large crowds when it was set in place.
“This type of architecture conveys a very rich, traditional, hometown-type of experience,” says J. Craig Rambo, president of architectural firm McGill Smith Punshon. The park will be professionally landscaped and have benches, space for outdoor cafés and Wi-Fi, and will be within walking distance from the offices, restaurants, and businesses that will make their home at Towne Centre. A new library is scheduled for completion in 2010.
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| The square features a prominent green clock tower and matching 57-foot-long by 8-foot-wide pedestrian truss bridge. |
The pond lies in the center of the new downtown complex and is a focal point of the development. The pond’s banks were lined with riprap in some areas, but needed more reinforcement to deal with the rise and fall of the water, as well as the freeze-thaw cycles. A Redi-Rock retaining wall was used to line the pond.
“The number one reason Redi-Rock was chosen for this project was aesthetics,” says project engineer Joe Kowalski, P.E. “The second reason was durability. With the freeze-thaw cycle here in Ohio and the water environment, we just had to have a solid block.”
The classic cobblestone look of Redi-Rock’s big block retaining walls tied in well with the appearance of the development. Though each massive block has nearly 6 feet of face, the cobblestone texture gives the appearance of six smaller blocks. This allows developers to achieve the look of a high-end professional landscape wall with the efficient and easy installation of a big block system.
The 7,000-square-foot wall lining the retention pond was designed to be 10.5 feet tall, with 1.5 to 3 feet of that buried. The ground surface below the wall is submerged and is inclined at 2H:1V.
The wall was constructed in a dry condition before the pond was allowed to fill. Crews from Sunesis Construction prepared the leveling pad by digging a 48-inch-wide trench the length of the wall and compacting the existing soils. The trench was then lined with 12 inches of No. 57 crushed stone and leveled. Installing a leveling pad to the engineer’s specifications ensured that the rest of wall construction would be level.
A majority of the project utilized Redi-Rock 41-inch series block; Sunesis placed blocks using an excavator and a person at the wall to guide the blocks into place. The engineering plans for the project called for a 4-inch-diameter flexible, corrugated slotted drain pipe and a permanent drain outside the wall to make sure the water drains from behind the wall properly. Kowalski also called for a 1-foot gravel drainage zone behind the entire height of the wall that allows the wall to drain properly. Because retaining wall failures are often the result of insufficient or improper drainage, preparing a proper base and installing drainage are critical steps that must not be overlooked.
In many retention pond applications, Redi-Rock walls do not need to be reinforced; these gravity walls rely on the massive size of each 1-ton block to hold them in place. However, in certain applications, engineers specify reinforcement to ensure the wall is stable even with the forces of moving water and other factors acting on it. The most common type of reinforcement for retaining walls is geogrid, a flexible, synthetic mesh fabric that is connected to the retaining wall blocks and extends behind the wall. Geogrid stabilizes the soil behind the wall, a necessary precaution in certain conditions.
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| The pond lies in the center of the new downtown complex and is a focal point of the development. |
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| The wall currently lines about one-third of the pond, but most of the pond is still lined with riprap and the natural bank. |
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| By designing this retention pond with aesthetics in mind, designers were able to capitalize on their stormwater solution rather than hide it. |
Because the soil at the Towne Centre site created global stability concerns, Kowalski, owner of Kowalski Engineering, specified a lightweight biaxial geogrid product for this retention pond. This type of geogrid has strength in both directions, whereas most geogrid products only have strength in one direction. The biaxial geogrid allowed installers to simply roll out the geogrid behind the straight sections of the wall, which saved on installation time. Ten-foot-long layers of geogrid were installed between the first and second courses of blocks, between the third and fourth courses, and between the fifth and sixth courses. Kowalski also specified geotextile fabric to be placed between blocks in the vertical seams to prevent gravel, sand, or sediment from migrating from behind the wall and seeping out the front.
“I typically recommend geotextile between adjacent blocks on the vertical seam, especially in the water, even though Redi-Rock’s uniform dimensions create a good tight seam between blocks,” he says.
Because the native soils were adequate for backfilling the project, developers saved money by not requiring that backfill material be imported. Since the wall was about 700 feet long, this proved to be a significant savings.
“We excavated and put down several inches of crushed stone and compacted it to give us our grade. After you put in the first course of blocks, it’s really simple,” says Sunesis Construction foreman Dave Hulley. “It [the development] is really top class.”
The wall currently lines about one-third of the pond, but most of the pond is still lined with riprap and the natural bank. Redi-Rock Structures of OKI will be supplying blocks to provide erosion control for another section of the pond.
“They really chose Redi-Rock for the looks,” says Roger Titkemeyer of Redi-Rock of OKI. “The functionality of Redi-Rock was key, but the aesthetics are what hooked them.”
The Towne Centre pond underscores the fact that stormwater management need not be an eyesore. By designing this retention pond with aesthetics in mind, designers were able to capitalize on their stormwater solution rather than hide it.
The project was awarded Water Application Wall of the Year in the 2010 Rocky Awards competition, which honors the best Redi-Rock walls in several categories.