Microtunneling Under the Zumbro River in Downtown Rochester, MN

Downtown Rochester, MN is experiencing a major economic development initiative to position Rochester as a global destination for health and wellness. The $5 billion project is being implemented over a 20-year period and began in 2014. With the proposed expansion comes the need for infrastructure expansion and capacity increases.

As part of the DMC initiative, Rochester Public Works department had a need to improve a sanitary sewer along 1st Avenue SE to 2nd Street SE, and the storm sewer along 2nd Street SE to 3rd Avenue SE, as well as a new siphon located from the 3rd Avenue SE Bridge from the Rochester-Olmstead Government Center to 2nd Street. The result was the 1st Avenue SE Relief Sewer for the Government Siphon J7825 project design. The full scope of construction began in May 2018 and is anticipated for completion in July 2020.

The bid was awarded to prime contractor Lametti & Sons, Inc. in March 2019 and crews mobilized to Rochester in May 2019.

One of the critical pieces of this project was a 393-lf., 36-in. microtunnel, that runs northeast from outside the main entrance to the Rochester-Olmstead Government Center, under the Zumbro River to emerge to the siphon connection on the east side, across the street from the Rochester Public Library. The 36-in. steel siphon casing was to be filled with dual 8-in. a 10-in. HDPE siphon carrier pipes and encased in cellular concrete upon completion.

While not very long, the tunnel is complex in nature and runs the gamut of varying ground conditions – from very soft to rock in a high-water table. The final 15-lf. of the run required emergence into the reception shaft from a full-face of sandstone and dolostone up to 1/3 of the size of the internal diameter of the pipe and 30,000 psi compressive strength.

Using an Akkerman SL38.5 microtunneling boring machine (MTBM) system, the alignment was accurately and successfully completed in January 2020.

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