Braun Intertec was retained to assist with renovation of the Humboldt Mill in Minneapolis with a new six-story, post-tensioned concrete structure built within the walls of the former mill.

A new ten-story, post-tension concrete structure (The Annex) was built adjacent to the mill.

Challenges

The adjacent St. Anthony Falls Heritage Center shares two walls with the Humboldt Mill, and the site contained large amounts of old footings, foundation walls and debris. It would be crucial to determine how to support and excavate sub-standard soils below footing bottom to avoid undermining mill walls and footings.

Solutions

We conducted a Building Condition Survey of the adjacent St. Anthony Falls Heritage Center, contributing to our knowledge of area soils, development and existing structures. We also led inspections and testing of installation of mini-piles used to support the building’s footings, where excavation would undermine the Humboldt and/or St. Anthony Falls Heritage Center foundation.

In addition to vibration monitoring during construction, we observed excavation of fill containing large amounts of old footings, foundation walls and debris. We also observed excavation of diving buried topsoil throughout portions of the site and that of alluvial and glacial soils used to support the building’s footings.

ICBO Certified inspectors with experience in providing special inspection and testing services were onsite during this project. We offered a special inspection and testing scope of services and provided a realistic budget based on expectations of the owner and construction team.

By working closely with the general contractor, we were able to provide quality services and recommendations that helped them secure the next phase of work. We were also able to provide the structural engineer with the comfort that qualified inspectors were reviewing the workmanship of the project.