Glensheen Mansion Serpentine Wall Helical Tieback Repair in Duluth, MN

Friday, June 6th, 2014 by Steve Gomez

Challenge

DBS was first contacted in 2013 to help design a tieback solution for the old serpentine wall at the Glensheen Mansion, which is owned by the University of Minnesota - Duluth. The decision to proceed with the project was made in early summer of 2014 as the final design was approved and materials were ordered.

Solution

The design engineers requested that the core holes be as small as possible, so the decision was to core 4” diameter holes in the wall. This decision along with a steep slope on one side leading down to a creek necessitated the use of handheld installation gear to install the helical tiebacks. The wall varied in thickness from approximately 12” at the top to approximately 36” at the bottom.

The (15) helical tiebacks were installed at a 10 degree angle, and the average installation depth varied from 15 to 21 feet with most tiebacks terminating at 21 feet.

The 1.5 inch round corner square bar tiebacks had one 12” and one 14” helix bearing plate, and they were installed with an average torque of 2000 ft. lbs. that provided approximately 10 kips of ultimate tension capacity.

Excavation, tieback installation and backfilling was all completed in one week.