Stable Construction Company uses soil nailing for its emergency stabilizing of the rock slope on U.S. Route 35E in southern Ohio.
On Feb. 10 Stable Construction Company (SCC) of Painesville, OH, was staging equipment to begin a soil nailing and rock scaling project to stabilize a landslide in northeast Ohio when the emergency call came in. This was to be the company’s first project with the Ohio Department of Transportation (ODOT).
Jack Hiller, vice president and construction manager of SCC quickly mobilized a crew and its equipment was relocated to a rock slide on U.S. Route 35E, about six mi. east of the Ross County/Jackson County line near Caves Road in southern Ohio.
This second slide had occurred at 4:00 a.m. and had toppled boulders onto a tractor-trailer rig causing extensive damage to the fuel tank, fuel lines, and axles. “It took a while to clean up because of the fuel spilled on the ice and snow,” said Kathleen Fuller, ODOT district 9 public information officer. The driver was not injured.
Contract pricing was already in place for the first project enabling ODOT to issue a Type-A emergency contract to begin work at the U.S. 35E site on Feb. 17, according to Hiller. “We’re a union shop,” said Hiller. Pricing is somewhat standardized according to the height, rate of slope and length of the rock wall or hillside to be repaired. He estimated the overall cost for the emergency repairs to be about $45,000.
The scope-of-work includes repairs to “the ledge and hillside adjacent to U.S. 35 following a rock slide that occurred between the 6 and 7-mi. markers of the route’s eastbound lanes,” according to an ODOT press release. ODOT’s engineers and geologists determined that other rocks or boulders along the hillside may be unstable and should be removed.
“Our team of construction engineers and highway management staff have been working as quickly as possible to expedite this project and restore the route to two lanes of traffic, and we are pleased that the contractors will begin working immediately,” said James A. Brushart, ODOT district 9 director.
The amount of rain that has fallen across Ohio this winter, along with near record-breaking snowfalls, are thought to be the cause of the landslide. “We’ve had freezing and thawing in the past few weeks, and that’s usually when we see slips like this happen,” said Fuller.
According to SCC’s President Hiller, soil nailing has been in use in various parts of the United States and around the world since the 1950s. The process involves drilling into soft soil, or soft rock such as shale or sandstone, until the drill reaches into the harder rock below. Then an epoxy rebar is inserted into the drilled hole and the hole is pumped full of a non-shrinking grout.
A staggered pattern of soil nailing holes are drilled up to 25 ft. (7.6 m) apart to stabilize the softer top layer of rocks that are often loosened by soil erosion or the kinds of freeze-thaw patterns Ohio has experienced much of this winter. “It’s a quick repair,” said Hiller. “We can usually do a 300 ft. slope in two to three days. The process is non-invasive and there is no excavation required. Unless the area will be covered with a wire mesh drape, there is no grubbing involved.” Grubbing is the removal of trees and other vegetation along a hillside or cliff.
The U.S. 35E repair involves approximately 500 ft. (152 m) of slope that reaches vertically about 100 ft. (30.5 m). The repair calls for them to incorporate both soil nailing and rock scaling.
To accomplish the scaling operation, Hiller’s five-person crew staged their tool trailer at the base of the slope and brought in a rented air compressor and generator.
“A standard four to five person crew climbs to the top of the slope, with a foreman-operator and laborer on the ground at the bottom,” said Hiller.
When the crew has reached the top, they tie themselves off and then rappel down the face of the slope using a spud bar and other hand tools to chink away at the loose rocks. When there is enough room under or around a loosened rock, an EPDM rubber (ethylene propylene diene monomer) bag is slipped into the space and a hose running to the air compressor is hooked up to inflate the bag which then slips the rock up and out of place, causing the rock to fall to the ground below.
“These are the same types of bags used by first responders to extricate accident victims from cars. We’re extremely safety conscious and hold a safety meeting each morning. We replace the rappelling ropes every two to three days, more often if they get wet,” Hiller said.
ODOT closed the eastbound lane of the highway a few minutes after 8:00 a.m. in order for crews seen working their way down the slope could safely dislodge the rocks and boulders. A mini-track hoe was parked nearby to load the debris onto trucks for removal from the site.
As soon as the larger rocks are removed, lane closures on the eastbound lanes will be intermittent. The westbound lanes have not been affected. Hiller expects all work to be completed by the end of February.
On-Going Problem on State Route 97
Hiller’s crew will then move back to the SR 97 slide site, which has been an on-going problem for ODOT since 2008.
ODOT and the Ohio Department of Natural Resources (ODNR) have been working together to correct an unstable roadside rock slide along SR 97, west of its intersection with SR 3 in Ashland County in northeastern Ohio since the summer of 2008. The slide occurred within the confines of the Mohican Memorial State Forest, according to an ODOT press release.
Work was originally scheduled to begin Feb. 15, but was put on hold until SCC could complete emergency repairs on U.S. Route 35E in southern Ohio’s Jackson County.
SCC will be stabilizing the rock slope along SR 97 using the same process of soil nailing and rock scaling of the shale and sandstone cliff face that was used in the emergency repairs in Jackson County. In addition, they will be grubbing the slope and anchoring a specialized high-strength wire mesh drape across the slope to contain any future falling rock into a catchment area.
SCC also will perform maintenance along U.S. 36 in Coshocton County. According to ODOT’s press release the total bid amount was $508,854, with the SR 97 portion estimated at $435,736. The work is expected to take 21 to 24 days to complete. No work will be performed in the State Park or in the river below.
After the trees on the slope face are removed, the soil nailing and rock scaling will be performed. After this process, additional soil nails will be installed to anchor the wire mesh drape.
The drape is environmentally friendly, according to both ODOT and Hiller, and will allow vegetation to grow through and around it. The drape will be approximately 70 ft. (21.3 m) high and approximately 460 ft. (140 m) across the face of the cliff. Anchor soil nails will be installed in a staggered pattern every 25 ft. across the top of the slope and will extend an additional 25 ft. farther up the cliff face.
ODOT defined the project: “SR 97 runs tightly between a large outcropping of weathered shale and sandstone formation and the State Scenic Clear Fork of the Mohican River. The sandstone has been undermined by erosion and natural weathering of the underlying shale, causing rock debris to fall into the eastbound roadway ditch and onto the roadway. These rock falls create an unsafe condition for the traveling public and have been a significant problem in the past.”
ODOT has estimated that it will require 1.707 acre (.69 ha) of right-of-way from the state forest land to allow for anchoring for the drape. Work is expected to be completed well ahead of the April 1 deadline mandated to protect the federally endangered Indiana bat during its mating season.
While these are the first two projects SCC has contracted with ODOT, Hiller was quick to point out that the soil nailing system has been in place for 60 years, and is utilized in places such as the rocky shorelines of the Pacific Northwest and in New York, Pennsylvania, and Maine.
This system, along with mine grouting is used heavily in Pennsylvania. SCC has done several projects in the Muskingum area to shore up the mines under I-70. “Holes are drilled and then pumped full of grout,” Hiller said. “SCC prefers to be unique in this niche market.”
For additional information visit, www.dot.state.oh.us