Sometimes excavation unearths surprises: pockets of debris, different soils, giant boulders-or a pipeline one didn’t know was there, as workers in Carmel, IN, discovered in summer 2010 when constructing a roundabout project.
“During excavation, we found an abandoned gas line that wasn’t in the plans,” explains Walsh Construction’s Charlie Gannon, project manager. “The original wall plans called for smaller bricks, which would have required more wall setback. That would’ve meant we would have had to dig out the pipe, recycle it, and dig further into the site’s easement. Cast-in-place walls would have required the same procedures.”
Gannon’s supplier, Reading Rock, suggested a solution. “Our small-block solution was in the original bid,” says Jill Fouts, LEED GA, of Reading Rock. “However, when that appeared unworkable, I asked if they’d consider big blocks-a gravity wall. I told Charlie that ReCon Walls might be the perfect solution.”
Since 2000, ReCon Wall Systems Inc. in St. Louis Park, MN, has licensed large blocks that create gravity walls, which can be built nearly vertical. ReCon blocks have face dimensions of 48 inches by 16 inches and depths ranging from 24 to 84 inches. These units, weighing from 1,000 to 4000 pounds each, are machine set, thus accelerating installation time and reducing manual labor. Made of wet-cast air-entrained concrete, ReCon blocks are designed to stand up to harsh conditions found in northern climates.
Walsh Construction and Reading Rock urged the city of Carmel to change the bid. “We worked it real hard, as we thought it was the right option. A ReCon wall requires just a little bit of setback, but mostly it goes straight up-minimal excavation would be required,” Gannon explains.
“With less excavation, using a ReCon wall was going to make the project cost about $1.5 million less, so Carmel went with it,” Fouts adds. “This project was the perfect opportunity, ReCon was the perfect solution, and it saved a lot of money.”
Carmel’s Keystone Parkway/Main Street Project entailed rebuilding the main intersection into the local high school. The main road was lowered, and an elevated a roundabout was built, eliminating traffic lights and time-consuming left and right turns. “Since it was for the school, we tried to do all the work during the summer vacation,” Gannon says. “We were working 70 to 80 hours a week to meet the schedule. Installation of the wall took about five weeks. We were building the roundabout as well, which included ramps up to the parkway to the cross street. Ramps, of course, made slopes, which had to be retained; four independent walls, one at each ramp, were installed. We actually hired a subcontractor to build the walls. About 15,000 square feet of wall was put in, at heights varying from 2 to 12 feet.”
The ReCon blocks were fabricated in Reading Rock’s home plant in Cincinnati, OH, a three-hour trip from Carmel. “But delivery wasn’t an issue,” Gannon says. “Reading kept up a good supply. To begin, we had a stockpile of blocks, but later in the project, blocks would arrive in the morning and we installed them by the end of the day.”
“We had product on the ground, and started building more blocks the previous December,” Reading’s Fouts reports. “It took about a month to get all the block needed to the site. And they put it in so fast! A machine, usually a skid-steer, lifts each block with a hook. There’s a guy hooking the block-ReCon blocks have a hook-ready notch-and another man on the wall with a pry bar who guides the block in place. A three-man crew, that’s it.”
The ReCon solution also saved the easement, and didn’t disturb adjoining residential properties. “Originally, the projected slope would have been 2:1-very steep, hard to maintain,” Gannon says. “With ReCon blocks, we raised the height of the retention, and most ended up 3:1 or 4:1 slopes. Ironic-we added a lot more square feet of retaining walls, at a lower cost.” ReCon offers four different textures, three of which create the appearance of natural stacked stone. In addition, ReCon blocks can be stained after installation to create a natural stone color complementary to the existing natural materials at the site. “We left the walls the natural limestone color, so no stain was needed, but we coated the walls with a sealer and an anti-graffiti application,” says Gannon. “Exposed soil was initially planted in grass, but the city plans some sort of landscaping.”
Although Gannon often uses Reading Rock, this was the first project on which he’d used the ReCon blocks. “I now think highly of the system,” he says. “I hope to use it again soon.”
When the Only Space to Build in Is “Up”
When parking was needed for the Cambridge Condominiums in Portland, OR, space was at a premium. “They wanted space for parking, below grade, but not take up the road,” explains structural engineer David Hall, SE, PE. “This was a difficult site to work with, as the condos offered prime land views of the river, Mount Hood, and Mount St. Helens. During the bid process, different contractors bid different types of walls, which then are typically approved by the city and the property owner, depending on the aesthetics of the wall fascia and costs. KeyWest Retaining Systems Inc. sold Lock+Load as the fascia.”
Installing Vancouver, BC’s Lock+Load retaining walls is similar to laying bricks in a bed of mortar; the soil backfill acts as the mortar, while the Lock+Load panel and counterfort behaves like the brick. As each row is placed, the soil backfill is used to grade and level each self-supporting panel, so it’s plumb, on line, and at the correct elevation. The row of panels is then backfilled and compacted, and the process is repeated until the finished wall height is reached.
“This retaining wall is a mechanically stabilized earth [MSE] retaining wall, which uses geogrid,” Hall explains. “Along the West Coast, depending on the soils, the back and front slopes, the surcharge placed behind the wall (traffic), and seismic considerations, 4 feet from the top to the bottom of the wall is about the maximum you can build a wall without geogrid. The majority of failures I’ve seen are from water intrusion, poor compaction, or poor construction. But Lock+Load walls are constructed to tolerate some settlement.”
Lock+Load panels rise vertically with very little setback, allowing walls to be built in tight spaces.
A “Welcome Mat” as Well as a Wall
Walls that are decorative allow an area to display an attractive “entrance” to its environs. When retaining walls were needed for the interchange of I-75 and Rt. 36 in Piqua, OH, the city, working with the Ohio DOT, created a structure that could be planted and that could display a “welcome” sign.
“It’s decorative, like a half-moon on each side of the highway, but then ODOT put in north- and southbound ramps, so the construction crew brought in a lot of gravel to shore things up,” explains Dean Fultz, who works with Dayton, OH’s Snyder Brick and Block. “As with most of its jobs, ODOT holds manufacturing to higher standard; it was looking for something cost-effective, which would be sustainable for a long period of time. WestBlock Systems was the perfect product for this application.”
For the past two decades, Tacoma, WA’s WestBlock Systems has produced a variety of blocks, from residential garden blocks to blocks for massive retaining or privacy walls. Aesthetics has been built into the blocks’ design; some products resemble hewn stone, and a color range is available to match local native rocks. For the Piqua structures, WestBlock’s GravityStone Edge product was used; as a WestBlock licensee, Snyder Brick and Block produced the blocks for the project.
“GravityStone is a strong, durable, economical block, which met all the project’s criteria,” Fultz says. “Around 1,750 blocks, at 1.33 square feet apiece, were used; the finished wall is 7 or 8 feet high at its highest point. Because of the blocks’ size, crews were able to fill up more square feet with fewer blocks. There was a lot of initial excavation on this project, and all the walls have been geogridded.”
Sydney, OH’s Eagle Bridge Co. did the actual construction of the walls. “This was their first time installing the product, but since then, they’ve done a lot more walls with WestBlock products,” Fultz says. “These blocks have to be laid by hand, not machine, but they still go up quickly; the project was finished under budget!”
GravityStone Edge blocks allow a graceful, curving wall. Differing stone sizes create a pattern that’s almost basket-weave.
Getting Things Locked Down
For certain soils, walls, or applications, it’s often advisable to anchor the soil or structure with further reinforcements. When the city of Sebastian, FL, needed to replace some of its Collier Canal seawalls, Everlast Synthetic Products’ vinyl seawalls were chosen for the job. However, in some spots along the 2.1 miles of the project, poor soil conditions were found, requiring soil anchors for the seawalls.
“This canal is the city’s primary stormwater retention pond, and since this blows off into the Sebastian River, it was necessary to keep silt out of the water, as well as protect the shoreline,” explains C.M. “Hap” Cameron Jr., vice president/director of marine construction for Palm Coast, FL’s S.E. Cline Construction Inc., the project’s contractor. “I knew the Everlast vinyl seawall would do the job, but to make the walls secure, we used Manta Ray earth anchors to keep the walls in place.” Manta Ray anchors are produced by Foresight Products of Commerce City, CO.
“Manta Rays are a known quantity for the anchorage of the wall,” Cameron says. “Usually we know how many Manta Rays we’ll need for job; they have a particular load-bearing capacity. Once we’d put one in the ground, we’d load-test it. If the test doesn’t hold right-for example, if there’s poor soil in that spot-we’d simply put more Manta Rays in, closer together. Was the spacing going to be 12 feet apart? Maybe it needs to be more like 6 feet apart, until soil conditions are better down the line. We’ve been using Manta Ray anchors for about 11 years. The product works-we’ve installed around 1,200 to 1,300 of them in the last year alone.”
The combination of vinyl seawalls and Manta Ray anchors solved many potential problems. The initial consultant on the project believed stone riprap could replace the crumbling seawalls. However, as the Collier Canal abuts 500 residential backyards, the heavy equipment needed to deliver and install the riprap would have wreaked havoc on the lawns. To place riprap for the 2.1 miles of the project, 1,000 dump trailers would have had to rumble down local streets. By using lightweight vinyl seawalls reinforced by Manta Ray earth anchors, only 10 flatbed trucks were required to deliver the materials. Because most of the vinyl sheets weighed less than 50 pounds, Cline Construction was also able to use smaller and lighter equipment on the job. As a finishing touch, the seawalls were topped off with poured concrete caps. “The reinforced cap acts like a beam, and environmental protection for anchors and steel beams,” Cameron explains.
“Everyone ended up happy,” he concludes. “The seawall gave homeowners more useable backyards, the watershed was protected from silt, and the price of this job, versus the initial riprap idea, saved the city about $60,000.”
Up a few states, ACF Environmental was called in to the Ocean Breeze waterpark in Virginia Beach, VA, to help secure a wall. “The park was adding new water slides this past spring,” says John Easom of ACF. “They took a big mound of soil, cut it, and made a level area and poured sidewalk, going from one amusement to another in the park. This 6-foot cut in the hillside needed a wall to keep soil from collapsing. This was quite a challenging job; first we had to make the hill, to block one amusement from another, then we had to tie in anchors. We drove in Manta Ray earth anchors, made a concrete rebar grid, tied the anchors to that, then sprayed it all with concrete to make it look like a boulder wall. It took four days to drive in all 36 anchors.”
Not only do Manta Ray soil anchors get around, but they also get to live in the fast lane. “Around Memorial Day, we installed Manta Rays in New Jersey for a big music festival,” he notes. “The anchors will hold up the bleachers. Insurance companies want to make sure everything’s secure, and the Manta Rays do just that.”
To get a better perspective on how much hillside was cut away for this project, note the US flag in mid-photo.
After less hillside, more lanes, and installation of retaining walls, Kenefick Park (the same flag!) is now visible from the Interstate.
Is It Rock, or Is It Boulderscape?
A portion of Interstate 80, which crosses the Missouri River as it links Iowa and Nebraska, needed to be upgraded. The river bridge was widened, and road lanes had to be added (from four to six or eight) on either side of the bridge. Because the river is surrounded by bluffs, the two-year project included cutting into hillsides, which meant retaining walls had to go in. Although both states participated in the project, Nebraska was especially interested in making the area look attractive, as it was, in essence, Nebraska’s, and Omaha’s, entryway.
“Another consideration: They didn’t want to get rid of other properties which adjoined the highway,” says George Schuler, PE, of Kansas City, KS’ The Judy Co. “So we designed and constructed a soil nail wall, which could go straight up-it didn’t have to be set back and cut into the right of way. That nail wall then received a 4-inch-thick base coat of shotcrete, which holds up the wall until the permanent coating is applied. Then Boulderscape comes in and puts on more shotcrete, which they mold, carve, and finish with an acid stain.”
The Judy Co., a geotechnical contractor that serves the Midwest and beyond, acted as a subcontractor for Hawkins Construction, which oversaw the entire project. Boulderscape of San Juan Capistrano, CA, did the finishing work on the wall. “Why did we pick someone way out in California? We’ve done four or five jobs with Boulderscape; very few companies do this type of work; we have a good relationship with them; and they’re willing to travel.”
This aerial shot reveals the project’s scope on the Nebraska side.
From soil wall to Boulderscape sculpture
The entire I-80 project was begun in fall 2009 and completed in spring 2011. “For our part, 72,000 square feet of walls were installed. The walls’ height varied from 10 feet to almost 30 feet,” Schuler says. “We build the nail walls one 6-foot vertical slice at a time. Actually, you start at the top and work your way down, so you don’t have to over-excavate-it’s a top-down construction technique. No geogrid is needed with these nail walls; geogrid goes with an MSE wall, which is built from the bottom up, because you need a layback for the slope, a safe area for workers. We can get right up against a right of way where MSE walls can’t, and with soil nailing we have to work on an existing slope-virgin dirt that’s relatively tight, not fill. This area contained loess soil, a lean clay; when it gets moisture, it loses strength. We had to design the wall with good drainage all through and around it. Boulderscape comes in to do its work when all else is finished.”
As part of the task was to give the area an attractive appearance, Boulderscape created areas of visual interest. “Those cutbacks, like alcoves in the wall, are there so drivers aren’t looking at a solid stone wall. Those areas resemble cut rocks, where the rest of the wall looks like huge bricks. When fully finished, the terraces will be landscaped, likely with native grasses, and backlit at night.
“Had they done a conventional slope and retaining wall, they would have had to cut into the right of way near the homes,” Schuler concludes. “Our method ended up cheaper, because it didn’t require all the earthmoving and using up space. Construction went very well, Boulderscape did its part very well-and the biggest selling point of whole project is how the end result looks. Nebraska DOT is very happy with the end product, which was done on time, on budget.”
A July 2009 downpour caused Midland’s drainage channels to flood, making it clear that the dirt channel would not withstand many more such rains.
Dual Duty: Holding Soil, Holding Water
“When it rains, it pours” might apply to Midland, TX. After long dry spells, a heavy downpour can send waves of water through the city’s drainage channels, so when a channel needs repair, the job has to be done-pronto. “We only average about 17 inches of rain per year,” says Scott Swonke, EIT, Midland’s civil engineer. “But we have quick and violent storms that can send 8 or 9 feet of water into these drainage channels.”
Swonke describes the project: “This 10- to 15-foot-deep, 30-foot-wide drainage channel, which runs along an alley where utilities are located, was built about 30 years ago. This is not “˜nature-made’ drainage; the channel was actually dug out. After all that time, the soil walls were nearly vertical; we had to shore them up. Since there’s so much hard rock around here, that’s probably the reason it held up as well as it did,” he adds. “This is one of the major drainage channels in this area. The watershed that drains through it is approximately 208 square miles. Since this part of Texas is pretty flat, all water drains to here. Most of the time, the channels are dry, but they must also contain lots of water during storm events.”
The project needed doing, but the ground was littered with “buts.” “We could’ve tried to use conventional methods, but we couldn’t use geogrids, which require much excavation, because we couldn’t hit the utilities, and there were plenty of them: natural gas, electric, telephone, two cable TV companies, water, sanitary sewer, and storm sewer. On the south side, electric wire was strung on poles, but on the north side, electricity was underground. Renovation of the channel would require some excavation, but we didn’t have much open land to work with; we didn’t want to destroy and replace the alleys.” The decision was made: “We had to go with a gravity wall system, and we chose Stone Strong.”
Stone Strong Systems of Lincoln, NE, produces gravity wall systems with large modular blocks that are set in place with machinery. As the blocks allow for vertical construction, Swonke could install walls without tearing up the alleys or any of the utilities. Local traffic also had to be taken into consideration. “Ward Street on the west side is a major collector; there’s a school along it, roughly a half-mile north of the project. Garfield Street on the east side is a major arterial that borders Midland College. Because the roads could not be shut down, all of the block installation was completed from inside of the channel.”
Construction began in September 2010. The section to be completed was about a half-mile long, between two streets. “Most of the channel ended up at a height of 12 feet of blocks with an additional 3 feet of concrete. As long as we were working there, we also took care of some “˜rehab;’ the alley’s south side was too narrow and unpaved. The alleys are used for garbage trucks and utility-repair access. The north side homes also use the alley for garage access. During construction, garbage trucks had to be rerouted on south side. The Stone Strong gave us the ability to get our trucks through; we added concrete pullouts to both sides so vehicles can pass more easily.” At construction’s end, the channel will become about 33 feet wide upstream of the channel midpoint, and then it will widen to 36 feet.
As of spring 2011, the project was not quite complete. “The wall itself is done, but minor bits of concrete work are ongoing. The channel bottom is already concrete, so we left the walls a gray color. We also constructed stairways for our personnel to get in and out, which are also good for safety if someone gets in the channel. Most homeowners next to the channel are very pleased, as renovation was obviously needed, and what we installed is attractive. The city’s pleased, too. This is the first job we’ve done with Stone Strong, and it worked great.”
