• Shoreline: TX River Flood Protection

TX Family Protects Home From River Flooding

Project Name: Vista Del Rio Wall #103

Customer Name: Vista Del Rio Residence

Design / Specifying Engineer: Civil Solutions Group, LLC

Block Manufacturer: SI Precast, Inc.

Wall Installer: Structures Hardscapes Specialists, Inc.

Project Location: San Antonio, TX

Year Built: 2008

Hold Back the Flood

THE CHALLENGE:

After a San Antonio area resident’s house was flooded three times by the Guadalupe River, he knew it was time for a change. Looking for higher ground, he bought property several miles upstream and started making plans for a retaining wall to protect his investment.

The new property was located approximately 20 ft. above the normal river level and consisted of a run of approximately 525’ along the river’s edge. On this property, the homeowner made plans to build a new home, a swimming pool and tennis court.

After seeing several failing retaining walls adjacent to the new property, the owner knew he needed something different—something engineered. The goal the owner had in mind was to provide a suitable construction area on top of the walls, in addition to protecting as many of the existing trees as possible. In addition, two requirements ruled the design of the wall—it needed to be a retaining wall that wasn’t going to fail and it had to look good.

THE SOLUTION:

To provide a shoreline protection solution, the general contractor, the Elan Group, contacted Redi-Rock manufacturer SI Precast to take a look at the site and come up with an engineered a solution.

Redi-Rock is a retaining wall solution that utilizes massive, one-ton blocks to harness the power of gravity and built tall walls 15 ft. or taller without reinforcement. Even taller walls are possible with Redi-Rock’s patented geoconnector. Redi-Rock has a proven track record in water application projects. The wet-cast concrete design of the blocks makes it hold up even in areas with freeze-thaw issues. Redi-Rock walls are available in three textures—Limestone, Cobblestone and the new Ledgestone texture—which give walls the “Essence of Natural Rock” look.

To design a solution for this project, the team called in Design Technician Phil Fassler from Civil Solutions Group (CSG) and Jeremy Banken, President of Structures Hardscapes Specialists (SHS) from Minneapolis to evaluate the site in person and come up with a realistic solution for the project.

The general contractor took Fassler and Banken on a water tour of the area surrounding the new home site. What the group found was a hodge podge of shoreline protection measures including stone and mortar walls and concrete bag walls. “These walls looked terrible and were all crumbling and allowing erosion,” Fassler explained.

The paramount consideration for the wall solution was what to do about the base of the retaining walls to prevent the river from undermining it. Michael Johnson, PE and President of Civil Solutions Group determined that the most effective solution would be to use sheet piling at the base of the walls. This allowed the area to be de-watered prior to wall construction. The loose river silts could then be excavated and replaced with competent material upon which to build the retaining walls.

The Redi-Rock wall design CSG drafted consisted of a two tiers which gave the home easy access to the riverfront. The design also provided the building space required for the home on top, and was the most aesthetically pleasing solution for the site parameters because it allowed for landscaping and a stairway. The walls, which stand approximately 9 feet tall each, are spaced about 15 feet apart. The lower wall is reinforced with geogrid, and the upper wall is a gravity wall. An additional 19.5 ft. tall reinforced wall completes the shoreline protection on the property.

By using Redi-Rock, CSG was able to design the upper tier of the retaining wall as a gravity wall. The massive size of each Redi-Rock block and the interlocking design reduced the amount of geogrid required, which saved on installation times and costs in addition to saving existing landscaping.

In water applications, there are two main factors that will determine whether a wall will fail or stand the test of time—the base and the backfill. Civil Solutions Group initially came on site, they discovered the river bottom was soft silt and clay at least three feet down.

Before construction of the wall could begin, a crew needed to divert the flow of the river around the construction site. To accomplish this, they constructed a sheet pile dam. The sheet piling extended 15 feet down into the river bed, providing a stable anchor for the wall.

Sheet pile construction began by a local contractor about two weeks prior to SHS showing up at the site and was approximately 75 percent complete when the retaining wall construction began. SHS excavated a ramp down to the sheet piles in order to conduct the earth work preparation necessary for the wall construction. SHS dewatered area behind the piles with pumps and excavated the loose material, then placed geotextile fabric in the bottom of the excavation. SHS filled the trench with crushed stone up to the base elevation for the lower tier.

The crew constructed the lower (reinforced) wall by cutting the embankment back approximately 18 ft. in order to provide room in which to operate their equipment. Geogrid reinforcement was placed behind the 28 in. deep Redi-Rock units and the reinforced area was filled with select granular material to minimize any settlement potential of the upper tier and the construction of the home.

The upper tier was constructed as a gravity wall using 41 in. and 28 in. deep Redi-Rock units. As each course of blocks was installed, SHS performed the second requirement for a successful retaining wall in a water application—they backfilled using crushed stone as specified by CSG. Adequate, engineered backfill prevents hydrostatic pressure from building up as the water levels rise and fall.

The tiered walls ended at the staircase location.  The 19.5 ft. tall reinforced wall was constructed the remaining distance to the property line and allowed the home owner to incorporate a boat house into the wall project.

The wall design at this location was pushed farther back into the property to provide a recess for the boat house that would remove it from the main flow of the river—thus better protecting the boat. This solution also helped to satisfy the Corps of Engineers, whose approval was required. The Corps was concerned about restricting the river flow with new construction along the water way. To meet the Corps requirements, CSG’s design took a little area from the north end of the property/river limits, and gave some area back on the south end of the property to maintain the balance of water flow.

THE OUTCOME:

In total, the 525 lineal ft. wall took about three weeks to install. The wall was completed in early 2008 and has seen two flood seasons come and go. Still, the 12,000 sq. ft. walls remain level and perfectly intact.

To learn how Redi-Rock performs in water applications, check out the Water Drag Shear information or Water Application brochure. Or, call 866-222-8400.

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