In November 2022 the Herrenknechkt TBM - value EUR10.63 million (USD11 million) - that was shipped from Germany has now been moved to the construction site on the Olentangy River Road in the city of Columbus, Ohio, USA.
Once assembled, the machine will be 122 m (400 feet) long and it will be used to dig the overflow tunnel from Olentangy River Road to Neil Avenue and Vine Street. Granite Construction, that had secured the contract on March 2021, is preparing the machine for its first launch to the south. The construction process for the EUR241.53 million (USD250 million) Lower Olentangy Tunnel (LOT) Project began in early 2021 and it's planned to be complete by September 2026.
The LOT is a key part of the City of Columbus’ capital-improvement program. The tunnel will provide adequate conveyance capacity and in-line storage to minimize sewage overflows to the Olentangy River, resulting in improved water quality and a reduction in pollutants in the water. The tunnel will divert overflows to the city's water treatment plant on Jackson Pike.
The designed alignment for the LOT consists of 17,000 feet (5,182 m) of 12-foot-diameter (3.7 m) tunnel, at depths ranging from about 43 (13 m) to 93 feet (28 m). The tunnel driven by TBM will be lined by precast concrete segments. The upstream shaft is located north of Ohio State University Campus, with the tunnel running south to the Arena District in downtown Columbus.
The LOT will connect into the upstream end of the previously constructed OSIS Augmentation Relief Sewer (OARS) at Vine Street. The upstream end of the LOT will be located north of Lane Avenue where three existing sewers, the Franklin Main, the Olentangy Main and the OSIS are in close proximity to each other.
There are three main shafts (large manholes and other structures to provide access and tunnel controls) for the tunnel: Vine Street (consisting of an upper and lower shaft), Gowdy Field near Third Avenue & Olentangy River Road and Tuttle Park north of Lane Avenue. The tunnel will terminate at the Vine Street Upper Shaft. At that point, the Vine Street Lower Shaft will serve as the starting point for the connector tunnel and will end at the existing OARS Shaft 6. The Vine Street Lower Shaft and connector tunnel will be constructed mainly in Columbus Limestone.
The main TBM shaft site is located at Gowdy Field (middle, launch shaft), a former landfill, west of the Olentangy River and State Route 315. The Gowdy Field Shaft is a slurry wall shaft. The TBM will first mine south to the Vine Street Shaft, then remobilize to Gowdy Field to mine north to the Tuttle Park Shaft (north).
The 2nd Avenue Tunnel will be constructed from the Gowdy Field South Shaft and mined beneath the Olentangy River to 2nd Avenue, using a 90-inch (2.29 m) micro TBM. There are two shafts along 2nd Avenue where relief structures are designed to connect to existing sewers. The Kinnear Subtrunk (KST) Relief Sewer is also being constructed by open cut and auger boring at 3rd Avenue west of the river and will be tied into the LOT at the Gowdy Field North Shaft.
The TBM will mine through mainly glacial deposits with cobbles and boulders; sand and gravel; silty sand and gravel; and cohesive silt and clay. The northern portion consists of a mixed face condition beneath the river with soft ground overlying bedrock and a weathered rock zone for the remainder.
Slurry wall construction at the Gowdy Field Shaft and secant pile construction at the Vine Street Shaft are complete and excavation is underway. Pre-excavation grouting has been completed at both shafts. The remaining shafts will be constructed in 2023.
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