C+S November 2022 Vol. 8 Issue 11

Environmental Studies Initially, a preliminary environmental study (PES) was developed and designers and environmental scientists worked with Caltrans and Stanislaus County during the design process to complete and clear the environmental technical studies. These studies included an Initial Site Assessment (ISA) for hazardous waste, Water Quality Report, Natu - ral Environment Study (NES), Biological Assessment (BA), Wetland Delineation, Section 4(f) for an adjacent public park, Visual Impact Assessment (VIA), and Historic Property Survey Report/Historic Resources Evaluation Report/Archaeological Survey Report(HPSR/ HRER/ASR). The environmental clearance documents were an Initial Study/Mitigated Negative Declaration (IS/MND) for the California Environmental Quality Act (CEQA) and Categorical Exemption (CE) for the National Environmental Policy Act (NEPA). A Wildlife Habitat During the design effort it was discovered that local wildlife, including birds and roughly 6,000 bats, had taken residence on the bridge, specifi - cally under the deck overhangs and between the bridge’s east exterior girder and the exterior bridge-mounted communication conduits. The team considered how these bats and birds could make the new bridge their home once construction was complete. Deck overhangs and bat houses mounted to both exterior girders were incorporated into the design of the new Hickman Road Bridge, which created ideal roosting conditions, a place where the wildlife could birth and raise their young. Within a few months after bridge completion, bats had already begun residing in the new bat houses. Maintaining Traffic During Construction Because the Hickman Road Bridge is such a critical piece of infra - structure in the area and there was not a reasonable detour available for rerouting traffic (the shortest detour length was 10 miles), it was determined that the existing bridge was structurally sound to remain in service until the new bridge opened. With 17 months of construction completed, the new bridge consists of a 750-foot long, 75-foot tall, five-span, cast-in-place, post-tension concrete box girder structure, supported by seat abutments at each end and intermediate two-column piers. Each pier is supported by two large-diameter cast-in-drilled-hole piles, ranging in diameter from 100 inches to 125 inches, and measur - ing up to 125 feet in depth. The bridge features two 12-foot traffic lanes, two 8-foot shoulders for bicyclists, and one 5-foot sidewalk for pedestrians. Additionally, 960 feet of roadway was reconstructed to conform the new bridge to the existing Hickman Road alignment. Overcoming Challenges Like with any infrastructure project, the design team faced numerous challenges. The first was justifying the need for a new bridge, given that the existing structure was still structurally sufficient. The design team developed conceptual designs and associated costs for a seismic retrofit of the existing bridge, a permanent repair on the existing bridge to protect the pier foundations from scour, and a bridge replacement. To compare the alternatives, the team prepared a life cycle cost analy- sis that was used as justification to replace the existing bridge. The second challenge was addressing the geometric needs for the roadway approaches that would place the new bridge on a parallel

alignment with the existing bridge; and so the existing bridge could re - main in service during project construction. To minimize the necessary roadway approach work, the team prepared a design that placed the new bridge as close to the existing bridge as possible. Despite this ef - fort, the necessary approach lengths still exceeded the HBP allowable limit of 200 feet at each end of the bridge. To address this, the design - ers prepared a long-approach justification memo citing road geometric design requirements, design speed justification, and safety concerns. Caltrans concurred with the justification and additional funding was secured for the long approaches. The third challenge involved numerous elderberry bushes and mi- grating fish species found at the site. Environmental scientists con - sidered two alternative road alignments for the new bridge to avoid environmentally sensitive areas. The right of way (ROW) costs were reviewed against the Valley Elderberry Longhorn Beatle (VELB) mitigation costs, and ultimately the alignment with increased ROW was chosen, saving Stanislaus County nearly half a million dollars in VELB mitigation costs. Now that the construction of the new bridge is complete and the exist - ing bridge has been removed, the new Hickman Road Bridge meets current seismic criteria, addresses the Tuolumne River channel erosion issues, and provides additional capacity and a safer crossing for ve- hicles, pedestrians, and bicyclists. The new bridge also carries a new waterline and other vital utilities across the Tuolumne River that are critical to the region. The $19-million project was funded through the HBP, Caltrans Local Seismic Safety Retrofit Program, and transporta - tion funds created by local sales tax measures. The Hickman Road Bridge is located just south of Waterford and crosses the nearly 150-mile-long Tuolumne River in Stanislaus County, California. Photo: Pretzer Photography.

MIKE PUGH, PE is an associate vice president and principal engineer with Dewberry in Rancho Cordova, California. He has nearly 40 years of structural design experience, including new bridges, bridge repairs and widenings, and seismic retrofits.



November 2022

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