Reede Construction Oversees New Rapid City I-190 Interchange Project Phased Around Weather Challenges
At the I-190/Silver Street interchange near Rapid City, South Dakota, an unusual layout caused safety issues as traffic increased over the years. "It's a very non-uniform diamondkind of a three-legged interchange as far as on- and off-ramps go," said John Gerlach, Project Engineer for the South Dakota Department of Transportation (SDDOT). "One of the on-ramps actually utilized a portion of a city road about a half-mile away."
However, as SDDOT looked at replacing the interchange, the deteriorating bridge (built in 1958) complicated the schedule. SDDOT let contracts for the construction at the end of last summer, too late to complete the new bridge or interstate lanes before cold weather arrived. With the curves and narrow width of the existing bridge, they didn't want two-way traffic while dealing with snow and ice. To overcome that challenge, SDDOT phased the project to complete offline work during the first winter and move two-way traffic to the northbound lanes this spring.
The new design by HDR Engineering, Inc., of Rapid City, features a single-point interchange. "We didn't have a lot of right-of-way in the area, so with the single-point interchange we were able to tuck the on- and off-ramps up close to the bridge," Gerlach said.
Prime contractor Reede Construction, Inc., of Aberdeen, South Dakota, is scheduled to complete the project in the fall of 2017, including upgraded underground utilities designed for the city by FMG Engineering, Inc., of Rapid City. The project is funded with $32.5 million from SDDOT and $1.7 million from Rapid City.
Storing a Hillside
SDDOT divided the project into four phases. In phase one, started last September, crews excavated a large hillside in an area needed for the new alignment. According to Gerlach, since the hill lay to the west of the current interchange, "Crews were able to do the mass excavation without disrupting any of the interstate traffic."
The contractor made a 60-foot cut and removed 150,000 yards of dirt. "The geotechnical engineers in their modeling anticipated that once we unloaded the hillside, there was some unweathered shale material down at the bottom that could rebound 6 to 12 inches," Gerlach said. To accommodate the possibility of a second round of excavation, "We cut down that hillside at the start of the project, then required the contractor to wait six months before building any permanent facilities."
The excavated dirt will be used in new embankments constructed over the next year. "We had to get the hillside cut down, but we couldn't put the dirt in its final position yet," Gerlach commented.
Instead, the team created two temporary stockpiles. "Once we start construction on the new lanes, we'll redistribute the dirt to the new embankments," he added. "The contractor has to double-handle the material, but we didn't have any other options."
Abutments and Sewers in the Cold
Additional work completed during the winter prepared contractors for the busy months ahead. For instance, "The new alignment shifted to the west of the existing interchange, which allowed us to start construction on the new bridge," Gerlach said.
The new single-span, steel girder bridge will stretch 208-feet-long with mechanically stabilized earth (MSE) retaining walls as abutments. At their tallest point, the MSE walls rise 25-feet-high. "We had a pretty mild winter so we got all the piling driven for both abutments of the bridge and built the MSE walls for the north and south abutments," Gerlach said.
The deck of the new structure features stainless steel rebar. "Due to the complexity of the interchange, we're striving for a 100-year design life on the bridge," Gerlach said. "Normally we use epoxy-coated rebar in our bridge decks, but to minimize maintenance, contractors bid one of two options for the bridge deck rebardual-coated zinc and epoxy, or stainless steel." Grangaard Construction Inc. of Watertown, South Dakota, was the low bidder on the contract with the stainless steel option.
The mild winter weather also allowed DRM, Inc., from Gillette, Wyoming, to work on sewer lines under I-190. However, "What they anticipated taking two weeks ended up taking five weeks to get the bore through," Gerlach said. "They ran into larger-sized cobble than expected. Their augers got stuck quite a few times and they had to extract the casings. A couple times they sent guys inside the casings to do hand excavation and break up the larger cobble in front of the auger."
Once the contractor finished drilling, they pushed 12-inch sanitary sewer pipes through the casings. Because the work occurred away from the critical path of the project, the delay didn't affect the schedule.
Flopping Traffic and Finishing Construction
In early March, SDDOT diverted all traffic to the existing northbound lanes of the interstate, where it will stay until contractors complete the new bridge and southbound lanes in phase two. With the new roadway template requiring three feet of undercut on all alignments, the contractor may need to bring in a select topping material. "We want a rocky material, rather than the in-place shale, which tends to swell when it takes on water," Gerlach said.
Phase two is scheduled for completion in October. As soon as traffic switches to the new alignment, work will begin on the northbound lanes in phase three. "We want all lanes open to traffic by mid-July 2017, prior to the Sturgis Motorcycle Rally," Gerlach said. The Motorcycle Rally brings hundreds of thousands of bikers to the area each year.
For the third phase, crews will work through next winter. "We'll have a new, wider bridge that's no longer in a horizontal curve; it's in a tangent and the vertical curve is a lot less severe than the old bridge," Gerlach said. "By keeping traffic two-way in this second winter, the contractor can do all the demolition of the northbound lanes and the old bridge to give them a jump-start for the beginning of the 2017 construction season."
The last phase of work includes utilities and paving on an adjacent street. Gerlach expects final completion of all project details by October 2017. In addition to safer and improved access for motorists traveling to and from Rapid City, pedestrians and bicyclists will benefit from additional paths and improved connectivity to downtown Rapid City.