Slopes Need More than Walls and Nails
When you're caught up with the day-to-day hurly-burly of operating a business, it can be easy to miss the opportunities for growth and specialization in the world around us. Technological advancements, governmental policy changes, and perspective shifts among property owners have all affected the nature of our work.
Often slope stabilization is now as much about making an environment ecologically friendly as it is about ensuring the safety and security of a property owner's assets. The environmental movement that was once considered a niche group has now grown in importance, and has affected everything we do.
The movement’s growth has, in turn, been mirrored by the development of certain new services and techniques in the work of slope stabilization. Read on, and I’ll show you how three different companies have matured and adapted over the years, flourishing on the cutting edge of slope stabilization work, and what lessons we might learn from their stories.
Coastal Design & Construction in Gloucester, Virginia, works on the edge of the country, literally. They specialize in shoreline work, making sure that the last slope, from the land to the sea, doesn’t creep away with the wind and the waves.
Greg Gardy, Coastal’s head estimator, says the company also does riparian work and wetlands restoration, but that shoreline stabilization is its bread and butter. When the sea is eating away the land, as was recently the case at the Naval Recreation Center in Solomons, Maryland, it can sometimes mean you’re reconstructing a slope as much as stabilizing it.
There, a stretch of embankment had begun collapsing, which increased sedimentation into the bay, reduced available land, and put nearby picnic pavilions at risk. The project, conducted through the Southern Maryland Resource Conservation and Development Board and the Calvert County Soil Conservation District, specified a revetment to stabilize the slope, and a beach to add recreational value.
That was all well and good, but there was one hitch; the clients didn’t want the company trucking in the materials. “One of the requirements for that job was that all the stone and sand needed to be delivered by barge,” Gardy said.
Fortunately, Coastal is well-versed in maritime material deliveries, and Gardy says it was actually easier to build from the water than it would have been from the land. “Given that we used about 4,000 tons of armor stone and 1,000 tons of bedding stone, using road trucks carrying 21 tons of stone each would have caused quite a bit of damage,” he said. “Not to mention, the job was kind of awkward to get to from the roadside.”
Instead, the crew parked their equipment at the toe of the slope, and hauled the materials directly down to the shoreline from the harbor. Gardy says this job is typical of shoreline stabilization work; the shore starts to retreat, and they’re called in to build it back up again.
However, he says that in recent years, the efforts to protect shores in Maryland and Virginia have been stepped up, thanks to grant money through state and county conservation agencies. Instead of simply replacing shore losses, the company used systems that ensure stability and restore ecosystems.
“We’ll create a shoreline stabilization system by building offshore breakwaters, and charging the area behind the breakwaters with sand,” said Gardy. “The way these things are designed, so long as they put enough sand in the system, create what we call ‘spiral bays’.”
In a spiral bay, the ebb and flow of the sand is still there, but it’s in equilibrium, and the shore isn’t losing three feet every year. In that stable system, you can then plant horsegrass and spartina grasses to create a ‘living shoreline’, and return marshes and wetlands to an ecologically-sensitive area.
Gardy says that with this kind of work, where the materials are so capital-intensive, it’s best to start small, and hire experienced employees. “On average, our people have been with us for a minimum of 15 years and they know what they’re doing,” he said. “It makes it a lot easier for us, and our clients tell me that our quality of work is really good.”
Training is also of paramount importance to Ashley Herndon, project manager for Adams Contracting in Buckeye, Arizona. Her slope stabilization projects sometimes call for scaling a slope back to a less dangerous position using explosives. “Rock blasting is using explosives and controlled blasting techniques to cut the slope back or to eliminate some of the mass rock buildup,” Herndon said.
Needless to say, anytime that you’re working with explosives, a lot of training and caution is required. “Every area that you blast in is a little bit different,” she said, “but you have to be ATF-cleared; you have to have a blaster’s permit, and go by all state, county, federal, local and DOT guidelines.”
Of course, most of us aren’t about to get certified to use explosives anytime soon, but according to Herndon, when it comes to drilling and blasting for rockfall mitigation, it’s the drilling that’s more important. “We started out as a drilling and blasting company,” she said. “As time went on, people asked us, ‘Hey, can you drill that? Can you drill horizontally?’ Drilling goes hand-in-hand with slope stabilization.”
As the company received more and work, it branched out into new rock- more requests for non-explosive fall mitigation techniques, like pinning mesh systems over rock faces to prevent collapses. It bears many similarities to soil nailing work—anchors driven into the slope provides stability, and a mesh ‘blanket’ spreads that stability to the rest of the rock face.
“Basically, you’re installing vertical rock anchors on top of the slope, then you’re using lacing cables and draping a high-strength mesh steel wire down the face of the slope,” she be pinned at the sides and top, but said. Sometimes that mesh will just other times it will be bolted in throughout.
Any way you slice it, access is a real concern with rockfall mitigation work. “You have to rappel down from ropes, use helicopters and specialty drills,” said Herndon. They even have a cage with a horizontal drilling rig affixed to it, which they raise and lower with a crane when they need to bring serious drilling power to large, vertical slopes.
Still, Herndon says that the work is always getting better. “Every year in the industry, materials change, engineering changes, and things continue to get better,” she said, “The rockfall barrier fences have become a lot more contractor-friendly, for example.”
A rockfall barrier fence is more or less what it sounds like, a steel wire fence designed to catch rocks before they get to the bottom of a slope. Nowadays, once the foundations are in place, putting one up is fairly easy, but that doesn’t mean that just anyone can do it.
“People say, ‘Oh, we can pop up a fence,’ but they don’t realize that you have to have specialty drill rigs to drill these foundation anchors in,” Herndon said. “They have to be set in the grout and the bars. You’ve got to tension the ropes; you’ve got to shackle and clip.”
Although most people in rockfall mitigation focus on work for DOTs and the Federal Highway Administration, Adams Contracting has found a lot of clients in the custom-homes market. High-end home buyers will build their houses on hillsides for the view, and then they protect their investments when gravity and geology combine to threaten them.
“In the last three to five years, we’re seeing more and more construction in areas that are failure-prone, because folks are running out of the best property to develop on,” said Jeffery Hill, director of business development for Hayward Baker Geotechnical Construction, headquartered in Hanover, Maryland. He thinks that this real estate trend is part of what’s driving the wider acceptance of specialty geotechnical solutions.
At Hayward Baker, one such specialty solution for unstable slopes that the company started using early on was soil mixing: blending unstable soil with wet grout or a dry binder to turn it into a cheaper version of concrete. It may lack the full strength of structural concrete, but it’s versatile, and used properly, soil mixing can significantly increase a slope’s factor of safety.
“Hayward Baker started doing grouting work in the 1970s, when Wally Baker brought some of the grouting techniques back from Europe,” Hill said. Still, he says it wasn’t until the reconstruction work after Katrina that grouting and soil mixing techniques really gained widespread acceptance. There, soil mixing’s versatility with wet soils and waterproofing capabilities became invaluable.
“In order to get the levees up to face the next hurricane, the Army Corps of Engineers had to accept some of these new techniques,” Hill said. “When the Corps accepts a new technique, it’s pretty hard for a state agency to gainsay it.”
The value of soil mixing isn’t just in its versatility, but in its use for structural slope failures. When a slope is failing due to geotechnical issues 20, 30, or even 100 feet below the surface, you need to dig deep to fix the problem at its source.
As soil mixing has gained in popularity, the specialty drilling rigs it requires have become more available.
Lately, Hayward Baker started borrowing batching systems for its grouting work from the rigs that the oil industry uses when cementing wells.
The adoption of soil mixing has been particularly important for protecting levees from failure. “A lot of levees in this country were built without sophisticated measures, and not built to the standards we have today,” Hill said. “So they have surficial failures quite often.”
To protect them, Hill will inject lime into the top 10 feet of a slope. The lime reacts with the clay so that it doesn’t take up as much water, thus stiffening up the crust on the levee. Hill says one important thing to keep in mind when using grout is that it has a high pH until it cures, and needs to be contained. “Once it cures, it’s inert. However, we do make berms and install erosion-control fences to make sure we don’t get liquid grout in our streams and waterways,” he said.
He recommends that contractors trying to get into this kind of work focus on surface problems at first. “Because of the specialty tools and the engineering required, there’s a bit of a barrier to entry here,” he warned, “but there are more tools available on the market for shallow failures.”
The story of Hayward Baker is one we see repeated in this industry time and time again: lesser-known geotechnical technique or technology gets dreamed up when the traditional answer isn’t enough. When it succeeds, it gets used again when the same sort of problem arises elsewhere, developing a niche.
Once word of that niche solution spreads, it reaches the ears of other engineers and contractors who might be facing a slightly different problem, but find that it works for them, too, and is even a better solution than the traditional route.
This is not to say that you should discard tried-and-true conventional techniques; after all, they became the convention for a reason. Rolled erosion-control products and hydroseeding are still fantastic at reducing or eliminating soil erosion on slopes. Retaining walls and soil nails can still stop structural failures dead in their tracks.
This evolution of design is simply how we progress, and positioning your business to partake of these new adaptations is critical to survival in the business world. Does your equipment have some uses you haven’t thought to put it to? Do your employees have past experience you could draw from?
Maybe you have an idea you’ve been toying with for years but never quite got around to implementing? You just might find that you have an untapped treasure trove. After all, with the real estate market expanding again, the challenges are only going to get bigger, and you need to be prepared to meet them.