The Coffin Golf Club in Indianapolis runs along the White River. Jim Blazek, a principal of D2 Land and Water Resource Inc., explains the problems faced when the river occasionally floods. “The river floods the course, and there is some erosion due to the floodwater coming up and flowing alongside the bank, but the larger issue was the floodwaters pouring back off of the golf course, down the steep slopes. There were five low spots along this side of the golf course that were acting as downslope flumes. The gradient was approaching 1:1 or 1.5:1. When you have that great amount of floodwater up on the flat area of the golf course going back down over that very steep slope, they were in essence acting like downslope flumes.”
Blazek explains that in order to overcome this problem, he used a variety of products, including the Geoweb cellular confinement system from Presto Products, a P550 turf reinforcement mat (TRM) from North American Green, coir logs, sack gabions, Presto’s Geoterra structural mat, and native vegetation.
“First [the crews] cleared the site,” says Blazek, “Like a lot of our nation’s rivers, this riverbank was littered with invasive plants-and concrete rubble and asphalt from who knows where-so they did a lot of invasive-tree and -plant removal. Then they started doing the dirt work, digging out the old concrete rubble and asphalt and other debris that was there. Some of the erosion had gotten to the point that some of the slope reconstruction areas were fill slopes and some of them were cut slopes.
“There were five areas along this river shoreline that needed to be repaired. Once they got an area ready, they would put down a section of the Geoweb, which would be secured and pinned in place. There was an anchor pattern that was associated with that in an anchor dredge, and once that geocell was in place, they infilled that with soil and then placed a native seed down on top of that soil surface. Then they covered that soil surface with the P550 TRM, which was secured with a very long and a very heavy staple, because these rivers stay inundated for such a period of time, and there’s all kind of stuff that comes floating down. You have to make sure you can keep the TRM in place long enough for the plant community to develop.”
He notes that because of the variable water height of the river, coir logs are used as a “transition piece” to help hold the rest of the elements in place: “We used them vegetated, in this instance, to ensure that the plant community does get successfully introduced.” Plants will grow in contour spots along the slope.
“After the TRM is in place over the native seeds, down at the bottom of the slope there’s a sack gabion that’s placed at the bottom of the geocell,” he says. “The bottom of the geocell-TRM composite is butted into the sack gabion. Once that part is all installed, vegetated coir log is placed bankward of the sack gabion, and right on top of the TRM-geocell composite. It will be secured in place down at the low bank with a 16-inch-diameter piece. Then a 12-inch-diameter log will be placed in contour with the slope at the overlap, and it will be staked in place. What happens with this type of system is you’ve got the geocell confinement in the soil with its anchoring pattern, and you’ve got the TRM protecting the seed bed, reinforced with native vegetation.”
He continues, “All of those elements work together to give you an incredible armor while the plant community develops. The total length is about 1,200 linear feet, and the bank from the bottom of the water to the top of the hill is probably a maximum of 40 feet.
“The one thing that has been unique in our area and that helped steer the owners and the consultants toward this approach was that even though there’s some use of gabion hard structure, and some use of geosynthetics, including plastic components that aren’t going to go away, the fact that you can integrate a native community of vegetation with those elements lets the DNR [Department of Natural Resources] and the Army Corps of Engineers and the Department of Environmental Management be more apt to permit such a project than if they saw a patch of riprap all over that bank.”
Route 309 Reconstruction
Route 309 had been a tiny two-lane road designed for low-volume traffic in Schnecksville, PA, northwest of Philadelphia. But because of considerable growth in the area, the roadway needed significant improvements.
“They needed to address the increased volume of traffic, as well as safety, because it was a tiny, winding little road that meandered down the hill and back up on the other side, going through a valley,” explains Jeff Harris of TenCate Geosynthetics. “It’s an environmentally sensitive area, so the idea was to replace the roadway that meandered down at the bottom. They cut the road on the top, and then in order to bring the elevation up, we used a reinforced slope technique, with the use of geogrids.”
Based on the requirements of the state, Harris selected the TenCate 10XT geogrid for the project, in addition to a Mirafi 1100NPA 10-ounce nonwoven geotextile (used as a secondary reinforcement), and a North American Green face wrap.
“The face wrap is an L-shaped steel frame basket, 18 inches by 18 inches, to give you a nice clean batter, so to speak,” says Harris. “It is filled with onsite material. They laid the baskets out; each basket is connected to the adjacent basket.” The insides of the baskets were lined with TRM.
“Then they put in about 7 inches of soil and compacted that,” he says. “Then, on top of it they put a layer of nonwoven geotextile.” Alternating layers of compacted soil and geotextile were added.
“Typically they put a layer of grid, then fabric, then grid, then fabric, alternating each layer. After a layer of grid was put in, the erosion control blanket was wrapped back over the grid, and they repeated the process all the way up.”
In places, the wall reached a height of 50 feet, requiring the geogrid to extend as far as 30 to 40 feet back. Another option would have been to build a bridge, but because the area is environmentally sensitive-as well as the significantly higher cost of a bridge-this option was not selected. “If you looked at the alternative to building that roadway, you would have had to do major excavation for the bridge piers and columns,” Harris says. “But this way, they were able to come in with minimal disturbance of the surrounding area. They were able to make that slope very steep as well.”
In addition, he says, “Typically, if you were trying to achieve the same thing without using a geogrid, which produced about a 0.5:1 slope, you’d have to probably be at about a 3:1 slope. So those slopes would come out another 30 to 40 feet on both sides. By using the geogrid, we were able to go more vertical. That way, we did not impact the wetlands down below as much.”
Birmingham Water Works
The Birmingham Water Works and Sewer Board serves some 600,000 people in five Alabama counties, and it had a problem. Engineer Jonathan Wilson explains, “The initial problem was the sludge coming from the backwash of the filters. At the filter plant, that water would go into the holding lagoons, the sediment would fall out to the bottom, and we would recycle the water off the top. The lagoons have been there over 20 years, and the sides were beginning to erode away. The clay liner was eroding, causing a lot of problems for the pumps. They would remove the sludge out of the lagoon bottom, and they were picking up rocks and other stuff. This was damaging the pumps and adding to our daily operational needs.”
Janice Reid of Strata Systems was called in to help the city, and she noted a couple of other issues at the waterworks. “They needed to form up the side slopes of these wastewater treatment ponds, but they were restricted on the cash that they could spend. There was also a major time constraint. The project needed to be completed by a certain time so they could get the ponds back in operation.”
After considering various concrete system alternatives, Wilson opted to treat the largest lagoon, Lagoon No. 2, with the StrataWeb cellular confinement system from Strata Systems. “We decided to use that because of cost reduction, as well as manpower and time reduction, since we did the project in-house, with our own crew,” Wilson says.
Reid adds, “The advantage to using the geocell was that, instead of forming the side slopes with welded wire mesh or some type of steel reinforcing, they were able to place the geocell in panels and form up large areas at one time, then fill them with concrete. It was very easy to cut and put into place in each of the areas of the pond. It went very fast, and because they saved time in not having to put together welded wire mesh or form up the concrete areas on the side slopes with steel, the project came in under budget. It also saved significant amounts of time as far as installation was concerned.”
Wilson describes the basic process: “We graded the slopes, removed all the sludge, laid down some filter fabric, then laid out the cellular confinement system. Then we poured the concrete in. It worked very well. It took really no time to lay the product down and stake it into the ground, and from there we just poured the concrete right in. We poured the top of the embankment first, to act as a weight to hold it down, then we worked our way down the slope, into the bottom of the lagoon.”
Additional best management practices at the site included sediment control measures such as silt fence and hay bales that were placed around the lagoon as mud was removed.
One challenge that Wilson faced, however, was that the project took place in the spring of 2010 during a rainy period. “It was so rainy,” he recalls, “that our biggest problem was getting the slopes to stay in place so we could put this system down. We would slope one side of the lagoon, lay down the filter fabric, then we would get a huge rain for two or three days, and there would be a channel running under the filter fabric where the slope had eroded away. So we would have to pull it all back, fill it in with some gravel, and start again.”
Nevertheless, the installation of the 23,000 square feet of the StrataWeb cellular confinement system still was completed on time and under budget.
A Geogrid Solution in Golden, CO
A private development known as Jefferson Office Park was recently under construction in Golden, CO. As Joe Kerrigan of Basalite Concrete Products in Colorado explains, “The city required a number of things, including a detention pond, to make sure the site was able to retain the water so it wouldn’t overtax the existing stormwater system throughout the area. Another important element was the aesthetics of the retaining wall matching the nature of the Golden area; the city wanted to make sure that it looked very nice.” Yet another concern was that no damage should occur to the US Post Office adjacent to the site.
Two mechanically stabilized earth (MSE) retaining walls were crucial elements of the site design, according to Dustin Bennetts, regional manager for Tensar International Corp. “In plan view, one wall was an oval-shaped-or wraparound-wall positioned to create a water detention pond. It allowed us to save useable space on the site compared with an increased footprint that a similar-volume pond would have required if constructed with traditional graded slope embankments.
“The second wall ran close to the property line between the US Post Office and the proposed Jefferson Office Park building site. This taller wall, around 20 feet in height, also allowed for more useable space to accommodate a larger building and more parking spaces on the otherwise sloping lot.”
For both walls, the Mesa Retaining Wall System was used. The system incorporates high-density polyethylene (HDPE) geogrid that has a positive mechanical connection to the Mesa modular concrete block units. The mechanical connection of the geogrid to the block, and the HDPE geogrid, allows the wall system to be used in applications such as detention ponds with the presence of water.
Doug Forry, principal with both Jefferson Office Park and Golden Builders, the contractor, explains some of the preparatory work that went into the project, particularly as it affected the construction of the larger retaining wall. “Being that size of a wall, it had to be engineered, so we contacted a soils engineer that we use, and he did the design on the wall,” he says. He has had some familiarity with the Basalite/Mesa block product in the past. He designed the wall, and told us how far back the geogrid had to go and the compaction we had to achieve.
“Based on that, we just excavated it out and started the project, making sure we hit compaction and the proper moisture levels all the way up. We met those criteria, and I think we came out with a pretty good product.”
Forry says that in some spots, the Tensar geogrid extends about 16 feet into the soil, especially where the wall height reaches 20 feet. He describes how he chose the building materials for the retaining walls. “I dealt with the structural engineers on designing the wall. I looked at some different products besides the Mesa block. There were some concerns about some of these alternatives when it came to the height of the wall-as far as the compressive strength of the block, for example. That’s why we picked the Mesa block. They’re not necessarily the cheapest for smaller walls, but when you get to a wall of this size, you don’t want to cut any corners. I would say, anything over 8 feet, pay real close attention to what’s going on.”
He was especially concerned that the adjacent post office be protected during and after the construction process. “We had a pretty good soils report and drainage study done on the site, so we knew exactly where any water that comes down is going to go,” Forry says. “We were very cognizant of that issue. We didn’t want to overload the post office with anything. With a wall that reaches 20 feet tall in one spot, I don’t want to see that thing come down and end up in their parking lot!”
He adds: “We’ve got a bit of a sloping site, about 6% or 7% across the site as a whole. When they built the post office, they excavated it down quite a bit to flatten out their area. In order to make our site work, we had to build it back up. The challenge was that this was the first wall of this type and size that we’ve ever done. We’re not a retaining wall contractor; we’re a general contractor. At that point, we were looking at keeping some of our guys busy, so we just did it ourselves. By paying attention to what the requirements were from the engineers, I think we surpassed what they were looking for. They were impressed at how straight the wall was.
“Mathematically, an important challenge was figuring out where the top of the wall needed to be. Because of the slope at the bottom, in order to get the top to come out straight, we had to vary where the bottom started. There was batter on the blocks, and this had to be taken into consideration with each step, so we would have to move things over a little bit. When we would step over to the next level down, we’d have to shift out a little bit to get that in line. That was a little bit of a challenge so we’d end up with a straight wall at the top.”
The work on this project began around December 2009, with both retaining walls completed by mid-spring of 2010. Both Kerrigan and Bennetts were quite impressed with the work of the contractor. “The biggest thing that I saw throughout the project was the regularity of the wall batter-all the way across the wall. It’s been in service now for about a year, and typically the first six months of such a wall is where you’ll see if there are any concerns in the wall integrity, and it’s working out perfectly,” says Kerrigan, the local distributor for the Mesa block system.
Forry understandably takes pride in the work of his crew. “A lot of work goes into one of those walls, but I feel confident that, a lot of years from now, that thing will be just as stable and straight as it is today. We’re at about a year now, and everything is in place; you can’t see a sign of any movement.
“But the quality of the walls has to do not only with the quality of the materials. Just as important are the skills and attention to detail demonstrated by all of our people that constructed the walls. Without the care taken during construction, the best material in the world will not produce a quality product. Our people make the difference in what we do.”
LaCrosse Municipal Airport
The LaCrosse (Wisconsin) Municipal Airport sits on an island within the Mississippi River, and expansion of the airport entailed an extension of Taxiway F into what had been several feet of water.
However, prior to placing fill, crews had to remove sediment up to 4 feet deep from the floor of the waterway. To accomplish sediment removal and dewatering, five different geosynthetic materials were utilized:
- Linear low-density polyethylene membrane to line the cell to manage effluent
- Geocomposite placed below geotextile tubes to facilitate dewatering
- Geotextile tubes to dewater the sediment
- Geogrid panels connected with hog rings to allow for placement of aggregate and sand layers
- Nonwoven fabric acting as a separator between the aggregate layer and sand layer
“The bottom line is, they’re extending the taxiway in the waters of the Mississippi River,” says Scott Nelson, vice president of Geo-Synthetics LLC. “They built a holding area and a dewatering area, we put a liner in there, and that’s where the geotextile tubes went. Then they dredged out where the taxiway is going to be, into the tubes, where they dewatered. They laid down a geogrid, put about 6 feet of rock fill on top of the geogrid, then came back in the spring and put a 12-ounce nonwoven geotextile on top of the rock fill, and a sand lift on top of that.”
The massive, whale-like geotextile tubes were an interesting feature of this project. “Those tubes represent one of the newer technologies out there right now,” he explains. “They are large fabric bags or geotextile tubes. We prefabricate them in the shop and ship them to the site, and the dredge is out floating on the water.” Dredged material-mostly water, but containing up to 8% solid material-is pumped into the tubes. “The water spills out and leaves the solids within the tube, so you’re capturing all the poor, mucky materials off the bottom of the bay,” he says.
“Those tubes had a 60-foot circumference and were about 200 feet long. That technology is not the cure-all to everything, but it does allow you to dewater large amounts of sediment.” The sediment dries inside the tubes. If no hazardous or contaminated material is involved, as was the case on this project, the tubes can be opened and the dried material spread onsite for use as mulch or topsoil.
Regarding the geogrid used, Nelson explains, “It was the BX1100 made by Tensar. Because we were floating it out across the water, we prefabricated it on a dry spot. We clipped it together with hog rings. They pulled it out and kept adding sections as they pulled it out across the water.”
Nelson notes that underwater divers were not needed for the project. “At one end, there was about a 40-foot area of dry land, so we drove posts three-quarters of the way out with pulleys on them, and then we ran a rope back to the grid. We put three pieces of grid together with hog rings, and then manually pulled them out, like pulling a window shade out. We pulled it out until we got to the back edge, added two more sections, pulled it out some more, and just kept pulling it out and added sections on the back side, until we got it out to where we wanted it to be. Then we started putting the aggregate on top of it, and sank it.”
The contractor and the project engineer both were surprised that this could be accomplished without the need for divers. According to Nelson, “They wanted to have divers down there to make sure there was proper overlap in the grid. But because it’s a polypropylene, by its nature it floats.” The material could be floated on the water, he explained, then sunk in place when the fill was added. “You’re going to accomplish the same thing without putting people in the water.”
The geotextile tubes used are composed of a high-strength geotextile. “On that site we used the Propex 4×6,” Nelson says. “It comes 15 feet wide, and we manufacture it in our shop in Waukesha, WI, into large rolls or tubes and ship it out.” Onsite at a dewatering area, the dredge pipe is inserted into the tube.
As the dredged material was directed into these geotextile tubes, a polymer was added to help coagulate the solid material. “By the time this fluid and sediment got to the tubes, it was flocculated into a cottage cheese consistency,” he says. “It stayed confined within the tube.”
He adds, “The last step of the process is that we had to monitor the outflow, because the water runoff is going back into the bay. We had to consistently monitor for chemicals and for the polymers, to make sure we stayed within the limits of what could go back in.”
In total, some 16,500 cubic yards of sediment were dredged and dewatered, allowing for placement of approximately 160,000 tons of fill material prior to the final grading and paving of the runway extension.
