During a large rain event in 2010, debris built up at the vertical piers of a triple cell concrete box culvert located at the only entrance to Plant 134 of the East Valley Water District (EVWD). The excessive amount of debris was left behind after fires swept through the area the year before. The debris damaged the culvert and completely blocked it, forcing the waters of Cook Creek to rise ultimately causing flooding and mudslides into an adjacent housing community. Identified as a major safety concern, the bridge needed to be replaced with an open, single span option.
As a solution, a 33' x 9.04' CON/SPAN® O-Series® Bridge System, 32' in length, which was selected as the best option for its single span and cost effectiveness, both short term — by utilizing less materials — and long term — by reducing the need for routine maintenance. After attending a presentation by Contech Engineered Solutions, URS, the project engineer, was intrigued by the cost effectiveness and waterway maximization of the O-Series especially due to their past positive experience with the CON/SPAN B-Series. Requiring less concrete per open area than any other precast buried bridge structure, the O-Series is the ideal blend of hydraulic efficiency and structural capacity.
During construction, continuous access to the plant was required to be maintained at all times. For this reason, vehicular traffic lanes were staged allowing safe, one-way traffic. In addition, to comply with the regulatory permits from the California State Fish and Wildlife 401 Permit and the U.S. Army Corps of Engineers 404 Permit, the Contractor was required to stay within the indicated limits of work within the creek as shown on the plans. Last but not least, no fill material was allowed in the stream bed.
In order to utilize the existing paved invert, the engineering team cut the existing concrete box culvert flush to the invert and placed footings on the outside of the paved floor. Following the footing setup, the Contractor was able to quickly and efficiently set the six precast, O-Series arches into place while also maintaining the required one-lane access into the plant. In just two days, the entire bridge structure was in place and the adjacent water main — originally affixed to the concrete box culvert — was successfully moved and attached to the precast headwall of the new structure.
Selected for its economic benefits and single span, which allows debris to pass cleanly through the structure, the CON/SPAN O-Series provided the best short and long term solution for the EVWD. According to Miko Aivazian, Engineer of Record with URS, "We selected the O-Series for several reasons such as the larger opening and because it would allow us to install the new bridge with much lesser environmental/permitting impacts."