Chicago's Unique Building, Innovative HDD Approach

By Jeff Griffin, Senior Editor | September 2008 Vol. 63 No. 9
Due to extremely tight space restriction. Mid America was forced to use a smaller HDD rig, but completed the bore on schedule.

When completed in 2011, the Chicago Spire will be the tallest building in North America and the world's tallest all residential building. With 150 floors rising to a roof height of 2,000 feet, the structure will rise higher than Chicago's Sears Tower, Toronto's CN Tower and the Freedom Tower to be built in New York City.

Located at the Chicago River's junction with Lake Michigan, the Chicago Spire will be a new focal point for the city's already impressive skyline.

Ground was broken for the structure in July 2007 when construction began on 34, 110 foot deep caissons that will anchor the building. Even though the structure has yet to rise above ground level, there is plenty of activity on the job site.

Trenchless construction already has played a key role in bringing electrical power to the new building. Last fall, Mid America Underground completed two difficult horizontal directional drilling (HDD) river crossings to bring power cable to the site, said Adam Bosch, Mid America president.

"We call it our ‘Power to the Spire' project," Bosch said. "With each crossing, 700-feet long at a depth of 70 feet under the river, a 300 foot design radius was required. Pilot crossings were parallel 15 feet apart under the Ogden slip at the north branch of the Chicago River at Lake Shore Drive, crossing from Navy Pier to DuSable Island.

"Upon commencement of the pilot hole, fluid circulation was lost within the first 50 feet. Excavation down to the bore hole provided knowledge of the presence of building rubble and trolley tracks,” Bosch said. "After removal of the obstructions and installation of a 10 inch HDPE surface casing approximately 40 feet in length, circulation was maintained through the majority of the four days of the pilot hole operation."

Second hole

The rig then was moved to the second pilot hole 15 feet away and drilling commenced. This second hole was completed in three days.

"The decision to drill both pilot holes prior to reaming was based on the fast approaching Nov. 15 city of Chicago moratorium to close excavations and restore pavement prior to winter," Bosch continued. "We had a standby drill unit ready to permit the option of reaming both crossings simultaneously if necessary."

The project called for four, 5 inch HDPE conduits to be installed in each of the crossings.