Retaining Walls: What You See and What You Don’t – Part 1
Editor’s note: This article from the archives first appeared in 2004.
What you see with many retaining walls these days is a fashion statement. No one likes to see just a concrete wall, and the facial elements of retaining walls have changed radically within the past two decades, just as pavers have changed the way driveways look.
Once made almost exclusively of large sections of poured-in-place concrete along highways or shorelines, retaining walls now get all dressed up to satisfy the architects and engineers who specify them, as well as the consumer end user. Designers and contractors now can choose from dozens of types of retaining walls, including various segmental blocks and facial styles. The opportunity now exists to carry a design through many areas of a site, such as from the patio to the garden retaining wall on a residential site.
Editor's note: This article from the archives first appeared in 2004. What you see with many retaining walls these days is a fashion statement. No one likes to see just a concrete wall, and the facial elements of retaining walls have changed radically within the past two decades, just as pavers have changed the way driveways look. Once made almost exclusively of large sections of poured-in-place concrete along highways or shorelines, retaining walls now get all dressed up to satisfy the architects and engineers who specify them, as well as the consumer end user. Designers and contractors now can choose from dozens of types of retaining walls, including various segmental blocks and facial styles. The opportunity now exists to carry a design through many areas of a site, such as from the patio to the garden retaining wall on a residential site. [text_ad] For the property owner, the only limiting factors are cost and having an architect who has kept up with the latest designs and isn't afraid to explore design concepts and products that originated outside of his or her own geographic area. Horizontal and Vertical Integration The Lake Michigan shoreline has a long history of erosion. One company in the area, Redi-Rock International, established in 1999 and has protected many properties along the shore and beyond. Today, there are over 130 Redi-Rock manufacturers around the world. Redi-Rock is owned by two generations of the Manthei family. "Our interlocking blocks average around 2,200 pounds each and have natural rock faces," says Ben Manthei, president of Redi-Rock. "The face is four feet wide and 1.5 feet high. Each goes back into the bank about 2.5 to three feet." The walls are designed to look like natural limestone rock, cobblestone, or split limestone with free-drain agate behind the face of the blocks. "Agate lets water in the soil go down to the bottom of the drain, and the drain carries the water out from behind the wall," explains Manthei. The business is about half residential and half commercial and includes many projects on Lake Michigan and around golf courses. One recent project built by MDC Contractors, another Manthei Development subsidiary, was the retaining walls for two high-end homes that a speculative developer had erected on a bluff 200 ft. above Lake Michigan. "The more expensive home sold first for $7.5 million," reports Manthei. "We did site grading and built retaining walls between and around the homes north of Harbor Springs, Michigan." Both homes were built on a steep grade, reached by driving 100 ft. up a winding road. The houses stand 75 ft. above the beachfront. "With these houses," says Manthei, "our biggest problem was moving the building materials on the steep access road. Before we built the retaining walls, you could walk out of the homes' basements across a small patio and to a big dropoff. Our walls were six to nine feet tall. From the house side, you see a natural, rock-faced, free-standing wall two feet wide, designed with curves." An 18-foot wall separates the houses and a turnaround area. The cost for grading and constructing the walls with mechanical geogrid connectors was a little more than $200,000. Sunken Tennis Court Another challenging project for MDC Contractors was sinking a tennis court for a condominium project in Petoskey, MI. The developer discovered that the planned tennis court would block the view from some of the condos. "We had to build retaining walls around three sides of the court," says Manthei. "These retaining walls have drain tiles to handle groundwater, rain, or snow." The tennis court walls are now 6–8 feet below the condominium building and 10 ft. from an already constructed garage. Eventually the tennis court's retaining wall will support some of the garage's weight. The garage limited the options on this project, explaied Jeremy Manthei, CPC, who at the time was site foreman for MDC Contracting and son of Ben’s brother Jim Manthei, who started making the firm’s segmental interlocking block in 1999. "Other types of retaining walls rely on soil tiebacks or geogrids to a higher elevation," says Jeremy. "Because of the closeness of the garage, it was extremely difficult to dig the footings for the retaining wall. This wall is about 100 feet long and 10.5 feet high. We started 7 feet below the bottom of the garage footings and placed 10.5 feet of soil around the garage." The cost for this project was about $250,000. Lake Bellaire Beach One of Jeremy's first projects was to shore up an eroding beach on Lake Bellaire. "The house had a big, natural rock retaining wall," he says, "but every winter the ice on the lake would push the boulders out of the water and onto the yard of the house. A product that will work in our freeze/thaw climate will work anywhere. In warmer climates you have to allow for more permeability. If the concrete contains microscopic voids and freezes, the voids will pop to the surface. "We built a three-foot wall with steps to the water about 150 feet long in the water behind the rocks and used geotextile filter fabric behind the wall that allows water to pass through and keeps out sand. We backfilled with sand. This was my first project built in water, so I learned as I went." Jim learned he had to run the wall at base elevation to the end of the steps rather than step up the step with the wall. The wall took three days to build and cost close to $9,000. "It is not unheard of, where large blocks are required, to install 600 feet of wall in one day," says Jeremy. "On taller retaining walls, we have a fantastic reinforced system called the Positive Connection System that using Mirafi geogrid in 12 inch strips to create a weight-independent connection,” says Ben. “We use 4000-psi wet-cast concrete mix."For the property owner, the only limiting factors are cost and having an architect who has kept up with the latest designs and isn’t afraid to explore design concepts and products that originated outside of his or her own geographic area.
Horizontal and Vertical Integration
The Lake Michigan shoreline has a long history of erosion. One company in the area, Redi-Rock International, established in 1999 and has protected many properties along the shore and beyond. Today, there are over 130 Redi-Rock manufacturers around the world. Redi-Rock is owned by two generations of the Manthei family.
“Our interlocking blocks average around 2,200 pounds each and have natural rock faces,” says Ben Manthei, president of Redi-Rock. “The face is four feet wide and 1.5 feet high. Each goes back into the bank about 2.5 to three feet.” The walls are designed to look like natural limestone rock, cobblestone, or split limestone with free-drain agate behind the face of the blocks. “Agate lets water in the soil go down to the bottom of the drain, and the drain carries the water out from behind the wall,” explains Manthei. The business is about half residential and half commercial and includes many projects on Lake Michigan and around golf courses.
One recent project built by MDC Contractors, another Manthei Development subsidiary, was the retaining walls for two high-end homes that a speculative developer had erected on a bluff 200 ft. above Lake Michigan. “The more expensive home sold first for $7.5 million,” reports Manthei. “We did site grading and built retaining walls between and around the homes north of Harbor Springs, Michigan.”
Both homes were built on a steep grade, reached by driving 100 ft. up a winding road. The houses stand 75 ft. above the beachfront.
“With these houses,” says Manthei, “our biggest problem was moving the building materials on the steep access road. Before we built the retaining walls, you could walk out of the homes’ basements across a small patio and to a big dropoff. Our walls were six to nine feet tall. From the house side, you see a natural, rock-faced, free-standing wall two feet wide, designed with curves.”
An 18-foot wall separates the houses and a turnaround area. The cost for grading and constructing the walls with mechanical geogrid connectors was a little more than $200,000.
Sunken Tennis Court
Another challenging project for MDC Contractors was sinking a tennis court for a condominium project in Petoskey, MI. The developer discovered that the planned tennis court would block the view from some of the condos. “We had to build retaining walls around three sides of the court,” says Manthei. “These retaining walls have drain tiles to handle groundwater, rain, or snow.”
The tennis court walls are now 6–8 feet below the condominium building and 10 ft. from an already constructed garage. Eventually the tennis court’s retaining wall will support some of the garage’s weight.
The garage limited the options on this project, explaied Jeremy Manthei, CPC, who at the time was site foreman for MDC Contracting and son of Ben’s brother Jim Manthei, who started making the firm’s segmental interlocking block in 1999. “Other types of retaining walls rely on soil tiebacks or geogrids to a higher elevation,” says Jeremy. “Because of the closeness of the garage, it was extremely difficult to dig the footings for the retaining wall. This wall is about 100 feet long and 10.5 feet high. We started 7 feet below the bottom of the garage footings and placed 10.5 feet of soil around the garage.” The cost for this project was about $250,000.
Lake Bellaire Beach
One of Jeremy’s first projects was to shore up an eroding beach on Lake Bellaire. “The house had a big, natural rock retaining wall,” he says, “but every winter the ice on the lake would push the boulders out of the water and onto the yard of the house. A product that will work in our freeze/thaw climate will work anywhere. In warmer climates you have to allow for more permeability. If the concrete contains microscopic voids and freezes, the voids will pop to the surface.
“We built a three-foot wall with steps to the water about 150 feet long in the water behind the rocks and used geotextile filter fabric behind the wall that allows water to pass through and keeps out sand. We backfilled with sand. This was my first project built in water, so I learned as I went.”
Jim learned he had to run the wall at base elevation to the end of the steps rather than step up the step with the wall. The wall took three days to build and cost close to $9,000. “It is not unheard of, where large blocks are required, to install 600 feet of wall in one day,” says Jeremy.
“On taller retaining walls, we have a fantastic reinforced system called the Positive Connection System that using Mirafi geogrid in 12 inch strips to create a weight-independent connection,” says Ben. “We use 4000-psi wet-cast concrete mix.”