The Changing World of Retaining Walls

Sept. 1, 2007

Free time is scarce in early spring for Mark Thomas. And that’s just how he likes it.

Late winter and early spring is when officials with the Bonneville Power Administration, the electricity generator PPL Montana, the US Bureau of Reclamation, and the US Army Corps of Engineers use Montana’s Kerr Dam to lower the water levels of Flathead Lake, the largest freshwater lake in the western United States.

And that’s when Thomas, one of the owners of Diversified Materials & Construction in Polson, MT, enters prime retaining wall season.

Homeowners along the 28-mile-long lake in northwestern Montana wait each year for the annual lowering of the water levels. It’s then that these owners shore up their private beaches with the installation of retaining walls of all sizes. For Thomas, this means steady work. This last spring, for example, Thomas and his crews erected 14 retaining walls for private-property owners lining the lake.

And this was considered a relatively slow year. Last year, Thomas’s company installed more than 2,700 feet of retaining walls around Flathead Lake.

“Due to heavy rains and warmer weather this year, the snow pack is coming off really fast. We are probably within two to three weeks of being done for this season,” Thomas said in early April. “They’re slowly raising the lake levels now. When we can no longer stay out of the water when we’re working on these walls, that’s our cue that the game is over.”

Thomas’s project is unusual: He and his crews have to act fast and work against continually rising water levels. But the fact that Diversified Materials & Construction is tackling several retaining wall projects is far from unique. As federal regulations restricting soil loss have gotten stricter, more contractors are turning to retaining walls to stop erosion on their job sites.

Manufacturers of these walls have responded, adding larger and more flexible products to their lines. Others are creating more retaining walls that are aesthetically pleasing, something that more clients are demanding. Today, contractors can find a variety of retaining walls for just about any job where controlling erosion is important.

As manufacturers roll out these new products, contractors increasingly are relying on retaining walls for their larger and more unusual projects.

Manufacturers say the popularity of retaining walls will only increase as developers continue building on lands once considered unsuitable for housing subdivisions and strip malls. The reason? There aren’t that many prime building sites left.

“We are constantly seeing our products used in major metropolitan areas that have pushed out so far that developers are having to go back into the center areas to find building sites that they previously passed on,” says Ken Headley, director of training and engineering with retaining wall manufacturer WestBlock Systems in Tacoma, WA. “These developers are building on sites that were once considered just horrendous places to work. They are sitting on water, in floodplains. The slopes are horrible. In places like Florida, where so many people are moving, a developer might buy 500 acres but find that only half of the land is buildable. So you build a wall, re-slope an area, and put in a retention pond. That’s where walls are really coming into their own.”

This all bodes well for the retaining wall industry and for contractors like Thomas who rely on them.

Quick Work in Montana
Each year, government officials authorize the lowering of Flathead Lake between 6 and 10 vertical inches.

Photo: Soil Retention Systems
Builders often use retaining walls to create terraced sites.

Property owners take advantage of this time to shore up their erosion protection. For many, this means hiring contractors to build retaining walls between their land and the waters of the lake. When the lake sits at its normal levels, most of these walls are under water and off-access to crews such as Thomas’s. Regulations forbid contractors from working in the waters of Flathead Lake.

Thomas and his crews work with private owners who have anywhere from 60 to 700 feet of lake frontage. They need retaining walls that usually average 100 feet in length and 9 feet in height. These aren’t unusual walls in either size or style. But Thomas and his crew members do have to install them as quickly as possible. They are working against time, after all, in the form of steadily rising lake levels.

“This is a slow year for us, but we’re still working hard,” Thomas says. “This is sort of a tradition here along Flathead Lake.”

Diversified Materials & Construction has turned to Charlevoix, MI-based Redi-Rock International, a manufacturer that specializes in large-block non-reinforced retaining walls. These walls don’t rely on geogrid reinforcing, something that requires extra space.

Because much of Thomas’s work requires him to build retaining walls along shorelines, he needs a product that works well in water. Geogrid retaining walls don’t, because the soil weight constantly changes with the level of water. So Thomas needed a wall that could stand on its own, without geogrid.

Photo: Soil Retention Systems
Demand in the industry is increasing for larger, taller walls.

By using Redi-Rock’s large blocks, Thomas’s company can build soil-reinforced retaining walls that can stand as tall as 15.5 feet without geogrid reinforcement.

Without these retaining walls, property owners along Flathead Lake would see their land gradually eaten away by constant erosion, Thomas explains. “Flathead is a good-sized lake. You can get some pretty good storms blowing across it. It’s not like with the Great Lakes or oceanic storms, but we’ve seen as much as 14- to 15-foot rollers pounding on our 6- and 7-foot walls. That’s a lot of abuse for a wall that’s not that tall.”

Thomas’s crews began building their walls in early January, when the lake levels, monitored by Kerr Dam, are lowered gradually. Some days, of course, are lost due to chilling temperatures.

This was the seventh season that Thomas and his company have tackled retaining wall projects around Flathead Lake. And it’s a source of business that Thomas doesn’t see drying up anytime soon. After all, if the water levels weren’t lowered in the winter, the damage caused to the properties surrounding the lake could be severe, he notes.

“The ice packs get good on the lake during the winter,” he says. “They have to lower the lake to get the water level away from all the docks the homeowners have. You can have these huge ice surges that would otherwise rip down the docks, causing hundreds of thousands of dollars’ worth of damage, if you don’t drop the water levels far enough, or if you do it too late. So this is a business we’ll be in for a long time.”

Photo: Mark Thomas
Protecting homes around Flathead Lake

Jake Manthei of Redi-Rock says more contractors are calling on his company when they have unusual projects, such as the one Thomas and his crew tackle each year around Flathead. Such projects require a special type of wall to fit into tight spaces.

“We’re perfect for projects that require walls between 10 and 15 feet tall but don’t have room for soil reinforcement. Our niche, really, is where you have existing underground utilities, water mains, storm sewers, things of that nature, and you need to build a retaining wall in tight spaces,” Manthei says. “Contractors use our walls when they are dealing with tight property lines and the next-door owner won’t let them encroach onto his property. In these cases, you don’t have room for geogrid.”

Redi-Rock’s largest source of business is tall non-reinforced walls. Because of this, the company is introducing a 60-inch block. Contractors can place two or three of these larger blocks at the base of a retaining wall and then pile more standard 41-inch blocks on top of them to build a taller wall without having to use geogrid reinforcement.

The variety of products that companies offer can sometimes be confusing to contractors. Redi-Rock officials hope to change this by offering a new 2007 design resource manual, both in hard copy and online form.

Building a Headquarters in California
It’s a big project: Snyder Langston Construction was hired to build a nine-story, $70 million office building to serve as the headquarters of the Pacific Life Insurance Co. The building would house about 1,000 employees.

Photo: Mark Thomas
Dock structures at Flathead Lake

Chad Olson, senior project manager with Snyder Langston, says his crews faced a challenge when asked to build a six-story parking lot for the employees of the office building. The parking lot had to be built over a series of sloping hills. To meet this challenge, the company installed about 250 linear feet of the 40-foot-tall mechanically stabilized retaining walls. To do this, the company turned to the Verdura retaining wall manufactured by Carlsbad, CA-based Soil Retention Products.

The Verdura features a strong connection between the wall’s concrete blocks and its geosynthetic material. This gives the wall durability and great strength, two ingredients necessary on the Pacific Life project.

The project’s design team had installed several layered terraces for the construction site. A lower terrace was designed to house the parking structure, while a higher terrace provided the site for the office building. In addition to combating erosion, the mechanically stabilized earth walls also had another function: to separate the parking structure from the office building.

The project encountered some delays when Snyder Langston had to truck in about 35,000 years of dirt to act as backfill for the retaining wall. The dirt located onsite was filled with clay, which had a high expansion index and would not have worked as a stabilizing material. But besides this, working with the retaining walls presented few problems, Olson says.

“Retaining walls have improved significantly over the years,” he notes. “Not only are the materials better to work with, the speed and accuracy of the construction of them has improved. People are getting more familiar with working on these kinds of projects. We had no real problems with these walls. And it was extremely easy to get the walls approved by the city.”

The Importance of Looks
The manufacturers of retaining walls have improved their products significantly, offering a wider variety of walls and developing them so that they are easier for contractors to build and install.

Photo: Mark Thomas
The walls require no geogrid reinforcement.

But in an equally important improvement, many manufacturers now are offering walls that are pleasing to the eye.

Boulderscape, a manufacturer based in San Clemente, CA, specializes in soil nail walls covered with shotcrete and carved and stained to resemble natural stone. Contractors working in residential and commercial areas where aesthetics are important-where residents, shoppers, or clients don’t want to stare at bare concrete all day-often turn to this firm when in need of retaining walls.

“We do a lot of work on sites where people want the walls to blend in,” says Steve Jimenez, vice president of Boulderscape’s commercial division. “Our product is for people that don’t want to be surrounded by a hard, ominous-looking wall. For instance, we’ll be called on when contractors are building walls around hospital parking structures. Our walls provide a soft and tranquil environment for a hospital facility.”

The importance of a wall’s appearance has grown over the years, Jimenez says. Many developers today are placing a greater emphasis on how well a wall blends into its surroundings. Boulderscape’s retaining walls meet this demand, building walls that resemble natural rock. The company specializes in replicating even the most detailed geological forms.

“About 15 years ago, this industry was all about producing a retaining wall that had longevity,” Jimenez explains. “People wanted a wall to hold a slope in place, and they didn’t want to have to worry about it for 100 years. That is as far as everyone went. It just had to look like concrete. Now there is a big push toward aesthetics. It’s not only about longevity now but also about how the finished wall looks. We can create just about anything now: a ledger stone, Egyptian stone, fractured stone. If it’s geological, just show us the geology and we’ll reproduce it for you.”

When TRC Solutions, with an office in Irvine, CA, began work in March 2006 on an expansion project at Hoag Hospital in Newport Beach, CA, the company turned to Boulderscape for the retaining walls it needed. The reason? The walls needed to look like natural stone.

Photos: Mark Thomas
At Flathead Lake, seasonally low water levels allow wall construction.

Subcontractor Condon-Johnson & Associates, with help from Boulderscape and TRC, installed a 1,500-foot-long and 30-foot-high wall to support a new parking facility at the hospital being built by TRC Solutions. Tom Deen of TRC says that working with the soil nail wall posed few problems on the site.

“Condon Johnson did the angled borings for the initial phase of the wall. They applied the shotcrete. All I can say is that I’ve been very impressed with the quality of the wall they put up. And it does look nice,” Deen says.

He says he’s not surprised that Hoag officials chose Boulderscape’s product. “The product is different. It’s unique. It doesn’t look like a cinderblock wall. When the entire project is complete and the pavement and landscaping are in place, the wall will look just like what it’s supposed to look like: the face of a cliff.”

Underground Parking in Virginia
When Headley from WestBlock Systems says that developers are turning more frequently to pieces of land that they would have ignored just 10 years ago, he’s not kidding.

He’s also not kidding when he says that this has become a boon for the retaining wall industry.

Contractors used his company’s non-grid-reinforced modular wall system in Waynesboro, VA, to surround an underground retention pond and culvert. A parking lot, serving a new waffle restaurant, rests atop this underground pond.

The reason the pond had to go underground? The building site, which sits alongside a busy highway, was not large enough to support a traditional retention pond.

Photos: Mark Thomas
Walls protect homes in Montana.

“It was an ideal location for the restaurant as far as commerce and traffic goes,” Headley says. “But it wasn’t ideal as far as the site itself goes. There wasn’t enough room for everything they had to build. They had to go underground, and that’s where our retaining walls came into play.”

Dwayne Whitson, owner of Stately Scapes, a construction firm in Cookeville, TN, says it took his five-man crew about a week and a half to finish building the WestBlock wall. The crew finished the project in early January. The wall extends 1,600 feet horizontally and stands 9 feet tall. And it did require some unusual steps.

First, Whitson’s crew poured concrete for the leveling pad or footer. Crews then poured the wall. When the wall stood above the top of the culvert, crew members poured concrete from the face of the wall to a drainpipe 8 feet way. This final pour locked everything in place.

Building the wall this way resulted in a more powerful structure, without the need for space-consuming backfill to provide extra support. This was critical, because the developers already were fitting as much as they could into a tight space.

“I’ve never put up a wall system like this before. But now I wish I could put up more types like it,” Whitson says. “It’s such a solid wall. There is no chance of it ever moving. I think we’re going to see a growing need for walls like this. Developers have used up so many of the fine properties out there. Now they are looking at the secondary properties tat have some issues with them. Walls like this give developers a chance to build on these secondary properties.”

Light Rail in Utah
Retaining walls are seeing a boost from another source: light-rail train systems. A growing number of communities across the country are building or expanding their light-rail systems. Such systems, municipal planners say, ease traffic congestion in growing urban areas.

Photo: Soil Retention Systems
Walls allow construction of a parking lot on a hilly site in California.

These projects often require retaining walls along abutments and overpasses. Consider Lock+Load Retaining Wall Systems in Vancouver. The company’s wall system does not stack on top of itself and is not supported by the units below it. Because of this, developers often turn to Lock+Load walls when they need taller, larger wall structures.

The builders of light-rail systems often need taller walls for their projects, and Lock+Load’s walls recently have been featured in a third light-rail transit system embankment on soft ground. David Ash, president of the company, says he expects to see even more of this type of application.

“The acceptance of mechanically stabilized earth walls in highway and railway projects has taken longer but is certainly coming into its own now,” he says. “It’s all about engineering progression. When you have a cost-saving idea, it’s usually the commercial and industrial part of the industry that calls upon it first. But the highway and rail industries take longer. Highway departments only want to build what works. Rail companies don’t care what it looks like, just as long as it’s going to be there forever. So they are a bit more cautious.”

Photo: Soil Retention Systems
Curved walls conform to the site.

Rail systems, though, are becoming more confident when it comes to retaining walls.

Kevin McFall, with Clearfield, UT-based Salt Lake City Commuter Rail Constructors, is the project director for the 44-mile commuter transit system expansion being built now from Weber County to Salt Lake City. The project, which began in 2005 and is scheduled to end in 2008, will have a $250 million price tag before it is completed.

As part of the project, McFall’s work crews had to build a 3,700-foot overpass structure in the Utah Transit Authority’s Ogden rail yard, located in Ogden, UT. The overpass consists of two bridges separated by an intermediate earthen fill, with long approaches on either end. One of the approaches stood between existing and new train tracks. Crews used Lock+Load’s wall system to build a wall to support two bridge abutments in this overpass.

The Lock+Load wall, which was built from October 2006 into February of this year, stands almost 0.6 mile long and is about 31 feet tall.

“There was a big advantage to that wall in that it goes up in one stage,” McFall says. “A lot of mechanically stabilized earth walls go up in two stages. You put up the wire mesh and fabric, let it settle, and then attach the precast at a later date. This all goes up at one time. That allows it to settle quickly. There is a huge schedule benefit to that.”

There were some challenges: Crews had to work around the Union Pacific freight trains that pass through the yard. The yard is a busy one, handling all the traffic that comes from the eastern portion of the United States on its way to points such as California and Oregon.

“There is a lot of traffic to deal with,” McFall says. “And you don’t want to interrupt it. We were fortunate that we were able to build the wall vertically without needing a lot of space. If we needed more space, we would have struggled not to have interrupted the train service.”

A Growing Business
Joe Friederichs, structural wall specialist with Contech Earth Stabilization Solutions in Minneapolis, says that the demand for retaining walls will only increase in the future. It’s important to remember, he says, that the retaining wall industry is a relatively young one.

Photo: Soil Retention Systems

“Our business has grown a lot, but it hasn’t been around all that long,” he notes. “The retaining wall industry is only 21 years old or so. In the 10 years that I’ve been doing this, the work has changed dramatically. Retaining walls are now more commonly accepted.”

Friederichs is also seeing a growing demand for larger walls. “When I first started in 1997, 5,000- to 10,000-square-foot walls were considered a good size,” he says. “Now we see 50,000- to 100,000-square-foot projects. It’s not an everyday occurrence, but we are seeing a fair number of them every year.” 
About the Author

Dan Rafter

Dan Rafter is a technical writer and frequent contributor.