Information from this article was first published in Demolition Magazine and is being reused with permission from the National Demolition Association.
What’s more dangerous and challenging than demolishing a 60-foot-wide, 2,000-foot-long structure composed of concrete, iron and wood? Demolishing it 80 feet off the ground over the largest freshwater lake in the world.
The City of Ashland, Wis., and Wisconsin Central railroad had both a historical and safety challenge on their hands when it came to deciding what to do with the long out-of-use Ashland Ore Dock. Built in the early 1900s, the structure once loaded vessels with iron ore mined in the area. The ships then transported the ore from Lake Superior through the chain of Great Lakes and out to the eastern seaboard for nearly half a century. The dock has been a significant landmark for the city, but it gradually fell into disrepair.
The city petitioned the state to conduct an engineering assessment study to determine the structural integrity of the dock. Comprised of a structural steel frame that held railroad platforms and rails on top, structural steel unloading chutes and a treated timber frame trestle that led up to the dock, the results of the survey and condition of the components varied greatly. The decision was finally made to tear it down.
Prepping the site, protecting the lake
After a few months of removing the pieces of the structure that were the greatest risk to the public’s safety, CN, the current owner, selected NDA member, Veit & Company, Inc., a specialty contracting firm located near Minneapolis, to oversee and perform the demolition.
“After gaining the necessary permits from the various organizations involved, we began removing the wooden trestles in the fall of 2011,” said Steve Hosier, vice president of demolition with Veit. “The next step was determining how to best approach the job. It’s pretty unusual to have a job that’s only 60 feet wide, 2,000 feet long and out in the middle of a lake, and 80 feet above the water.”
As well as the structural challenges of the dock, the Wisconsin Department of Natural Resources regulations required that Veit’s demolition team ensure none of the concrete, iron, wood or other debris fell into the surrounding water, which reached depths of 24 to 28 feet below the surface. “The city’s intake for fresh water supply is located just down from the structure,” said Ryan Olson, demolition general superintendent with Veit. “If any demolition debris entered the lake water, it had the potential to affect the city of Ashland’s water supply.”
To meet this challenge and ensure no debris fell into surrounding Lake Superior, the Veit team spent three to four months prepping the site for demolition, which included covering open-water areas at the base of the dock with steel plates and developing deflection panels and barges – the first of several innovative fabrication projects the company designed and constructed as part of the project.
The next fabrication project proved a bit more challenging, however. Working at 80 feet in the air, the material had to be contained when it fell off the dock. In order to keep the debris within the footprint, the demolition team constructed deflection panels that were attached to barges floating alongside the dock, which would catch the rubble and keep it away from the water. The panels and barges were designed and fabricated at Veit’s shop and then assembled and modified at the jobsite. As a further precaution to keeping the water safe from demolition debris, the Veit team implemented a 28-foot geo-tech fabric turbidity curtain below the water surface, essentially encasing the immediate work area and separating it from the lake.
Taking demolition to new heights