The removal of an early 20th century sawmill and pulp grinding facility involved extensive planning and engineering. The difficulty and technical challenges of this project stem from the fact that they are located on top an active dam on the Willamette river in Northwest Oregon with no land access to the work site.

Starting in 2020 Northwest Demolition and our engineers began planning a removal method. This planning of almost 2 years involved figuring out how to deliver and operate heavy equipment at the site. This involved the dismantlement of Northwest Demolition equipment, barge transfer and reassembly of the equipment on the elevated sawmill floor. Significant engineering was required to assess the operating floor, which is more than 30’ above the floor of the dam facility. Our team engineered, designed and constructed various bridge systems to carry and spread the load of the heavy equipment as it moved through the demolition process. The largest item, a high reach excavator, weighed more than 110,000 lbs and required steel bridge systems to transfer the load to supporting girders preventing the collapse of the floor.

Prior to and during the demolition, a significant hazardous materials effort took place. This work involved asbestos abatement, oil removal and the collection of universal wastes.

Our teams implemented engineering checks throughout the process to measure deflection in concrete and wooden floor systems. These checks, using laser, measure acceptable deflection of each building structure where work was being conducted to insure that the more than 100 year old structural members were able to support the active load.

The entire structure was first demolished to the top of the dam operating floor. Subsequent to this work, equipment was again disassembled and lowered through a demolished section of floor for begin demolition of the lower floors from the basement level. All of the hoisting for this work was completed with a sectional derrick barge with limited capacity and radius which involved several critical lifts.

Materials generated from the demolition were all transferred via barge upriver where they are transferred to truck for offsite recycling/disposal. Working on and over the water presented substantial environmental and physical risks. Debris boom and oil booms were deployed and positioned continually throughout the project to mitigate any potential migration of debris from the site. Much of the work was completed over the intake of an operating power plant which remained operation al throughout the project. Catchment systems for potential demolition debris were deployed over the intake area as the mill buildings to be demolished were less than 3’ away from the operational powerhouse.

River conditions were also a challenge and work required flexibility to move marine assets in and out of position to account for power generation and safety for high water.