16 MARCH 2024 WorldWide Drilling Resource® One-Year Turnaround for New Bridge Adapted from Information by Waka Kotahi The Coromandel, renowned for its pristine beaches, misty forests, and laid-back vibe, is one of New Zealand’s most popular destinations, but its tranquility was threatened in January of 2023, when a series of rain events, including a tropical cyclone, caused a section of roadway on State Highway (SH) 25A between Kōpū and Hikuai to crack and eventually slip away into a gully. Waka Kotahi, New Zealand’s Transport Agency immediately began geotechnical investigations to help decide on the best option to reinstate the critical thoroughfare. This included drilling boreholes and excavating test pits to assess the stability of the underlying foundation at the site and surrounding area. There were three main options for reinstating the highway, which saw around 3000 vehicles using it each day. Each of the three options were investigated at the same time so authorities could go forward as quickly as possible. “We don’t know which option is most feasible yet. The right solution cannot be established until the geotech work is complete. We know the rebuild must be resilient and as timely as possible. We understand how critical this highway is for Coromandel residents, businesses, and visitors,” said Jo Wilson, Waka Kotahi’s regional manager of infrastructure delivery. A steel bridge (rather than a bridge with concrete beams) was determined to be the fastest to construct. By the middle of October, the first stage of bridge deck construction was started, with three spans of girders already in place. Another achievement was the completion of the abutments, with a team pouring concrete for the wing walls. The next challenge was forming the deck surface with 138 precast reinforced concrete slabs and installing 44 precast side barriers. All during the bridge build, slip stabilization continued with soil nailing. To access the slip face, a caged drill rig was used. The team worked day and night shifts to drill holes into the slope at a slight downward angle, insert reinforcing bars, and grout them in place to ready the area for mesh installation. Waka Kotahi built the 406-foot bridge in record time by being able to use a similar bridge design from another project, allowing them to start ordering materials and begin work before the SH25A design was finalized. The precast deck system and a lot of overtime and night work allowed all teams to keep in sync with each other and stick to a very tight schedule. The route was reopened in time for Christmas, with some earthworks to be completed later, such as removal of temporary bracing under the bridge which would cause only minor traffic delays. C&G Bridge nearing completion. Aerial view of the slip.
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