The South Dakota Department of Transportation set a drainage construction milestone with an emergency culvert pipe replacement project on Highway 34 in Buffalo County, east of Fort Thompson. It marked the first time that the agency designed reinforced concrete pipe (RCP) energy dissipater sections for use under a main roadway and employed the new Standard Installation specification for installing the pipe.

South Dakota DOT engineers met the challenge of replacing two failed corrugated metal pipe (CMP) culverts, located 200 ft. apart, that had reached the end of their service lives. They specified RCP that could accommodate an internal energy dissipater design. Local concrete pipe producer, South Dakota Concrete Products, Pierre, used the concrete pipe industry's PipePac 2000 software to pinpoint a design that could be manufactured in the shortest amount of time. The SDDOT engineers accepted the PipePac design, and the project commenced immediately to avoid any further deterioration of the roadway and disruption to traffic.

Fall failure

The outlet ends of the existing CMP culverts had partially collapsed and separated during a storm, eroding a 25-ft. embankment up to the edge of the asphalt pavement. In mid-September 1999, the DOT contacted South Dakota Concrete to check on the availability of RCP for this emergency repair. The existing culverts were buried under approximately 26 ft. of fill at the centerline of the roadway. Using the normal DOT bedding specifications, shear steel would have been required in the RCP, which would have added several weeks to the required production time while waiting for delivery of the steel.

South Dakota Concrete staff used PipePac to come up with a pipe bedding design that eliminated the need for shear steel. By using the Standard Installation Type 2 bedding, the use of shear steel was eliminated in both the 72-in.-diam. and 84-in.-diam. concrete pipe. This design allowed production to proceed very quickly, with product shipment beginning the third week of October and carrying through to November 2.

Having met the challenge of delivery of the required quantities, sizes, and strengths of reinforced concrete pipe, the DOT took advantage of a nearby grading project being completed by Schwiegert Construction. Through-traffic on Highway 34 was already detoured one-half mile away because of the grading project, making the required road closure easier. The culvert pipe replacement project was change-ordered onto the existing grading project, thus bypassing the normal contract tendering process. The change-order allowed the project to be completed prior to the end of the 1999 construction season. This is not common practice by the DOT, but circumstances called for a bold plan.

Culvert reconfiguration

Each of the 72-in.-diam. concrete culverts was sized the same as the culverts being replaced. However, the difference in the new concrete pipe installation was the inclusion of the energy dissipaters between lengths of 84-in. RCP running up to the outfalls. The use of the precast dissipater rings between lengths of 84-in.-diam. RCP solved significant outlet velocity problems.

The rings were selected after review of energy dissipater options in the Federal Highway Administration's HY8 Hydraulics Program. One of the culverts had a 100-year flow of 344 cu. ft. per sec. (cfs), and an outlet velocity of 29.6 ft. per sec. (fps). The 84-in. dissipaters reduced the outlet velocity to 11.2 fps. The second culvert had a 100-year flow of 328 cfs, and an outlet velocity of 25.3 fps. With the 84-in. dissipater pipe, the outlet velocity was reduced to 11.2 fps. This resulted in substantial savings in the size of the stilling basin needed for outlet protection.

All the pipe joints for the RCP culvert and dissipater sections were tied with specially designed tie bolt assemblies. The 84-in. dissipaters had joint seal around the entire joint, while the 72-in. pipe was installed with joint seal in the bottom third of the pipe. All joints were wrapped on the outside in geotextile fabric to prevent migration of fines.

The Highway 34 culvert replacement project was completed successfully within a very short construction period because of the close cooperation between the South Dakota DOT engineers, the concrete pipe producer, and contractor. It is yet another example where reinforced concrete pipe was used in an innovative way by people willing to accept new age pipe design tools and bedding standards. The South Dakota DOT recognized the opportunity to develop a long-term solution using the latest in concrete pipe design and technology.

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Adapted from a Summer 2001 report in American Concrete Pipe Association's Concrete Pipe News. Author Dan Painter is a sales engineer with South Dakota Concrete Products, based in Pierre and operating plants in Mitchell and Rapid. South Dakota Concrete operates within the Concrete Pipe Group of Cretex Cos., Elk River, Minn.