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Kaibab Paiute Moccasin Wash Bridge

Pipe Spring, Arizona

Bridge Replacement


Kaibab Band of Paiute Indians


High Road Engineering, Inc.


Interstate Rock Products, Inc.


Fall 2015

Technical Description:

• Product: MULTI-PLATE® Round with beveled ends
• Diameter: 25'-0"
• Length: 138 LF

With a history of flash flooding in the area, it was little wonder that a bridge replacement was needed along the Kaibab Paiute Moccasin Wash in Pipe Spring, Arizona. The original crossing would get washed out completely nearly every year, and the Kaibab Band of Paiute Indians was routinely replacing the small culvert and repairing the road. While the road was washed out, drivers were diverted four miles along another route. With funding from the Bureau of Indian Affairs through the Tribe's Transportation Department, this project was designed and constructed to provide a permanent bridge structure and roadway across the wash.

The Tribe hired High Road Engineering, Inc. (HRE) as the civil engineering firm to design and administer construction for the project. Having heard of the success with a similar structure in the nearby town of Kanab, Utah, HRE reached out to Contech Engineered Solutions to help assist in the design of a permanent structure.

Moccasin Wash was analyzed to determine the most effective bridge type and size with the hydraulic capacity for a 100 year storm event. The drainage basin area is 16.67 square miles with a 100 year storm discharge of 4,680 cubic feet per second. Several alternative bridge types and pipe culvert sizes were analyzed but, in the end, a large 25' diameter round MULTI-PLATE® structure, 138' feet in length was selected as the best option. The MULTI-PLATE structure required 14 plates to make a full ring and, due to the size and height of cover, was specified at 1 gage.

The site conditions posed a challenge due to erosive sandy soils and the need to design for large monsoon type flood events which had previously been encountered in the wash. Flowing sand was encountered while boring test holes near the creek, and it was determined that the material could provide little structural support. The round MULTI-PLATE shape has the stiffness needed for the backfill heights and the hydraulic characteristics needed for high flows. The standard round pipe is also less costly to manufacture and install, while providing a factor of safety against any blockage from debris or silt.

Several end section types were considered but in order to comply with AASHTO LRFD design and help prevent undermining and scour, a step-beveled end treatment with a concrete cut-off wall and concrete slope collars for protection was selected. This solution provided constructability, cost savings and use of on-site fill materials outside of the pipe zone. Also included in the design were gabion basket bank protection to mitigate flood erosion of the bridge and road embankments. Contech supplied the Maccaferri 11 gage, galvanized twisted wire gabion baskets which were placed on the upstream and downstream embankments covering over 1,300 cubic yards.

Once the MULTI-PLATE was delivered to the site, the contractor, Interstate Rock Products, Inc., assembled and installed the structure in a successful manner.

“The MULTI-PLATE product proved to be the best solution for my client’s project," stated Elisabeth Whitlock, PE, President of HRE. "The Tribe is in a remote location, and the MULTI-PLATE bridge was able to be delivered directly to the site in manageable pieces. The plates assembled easily and quickly which equated to construction cost savings.”

Technical Description:

• Product: MULTI-PLATE® Round with beveled ends
• Diameter: 25'-0"
• Length: 138 LF

800-338-1122 |

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