In Ketchikan, Alaska, much of the area’s income is derived from tourism, as well as vessel repair and manufacturing. Two viaducts, supporting approximately 17, 000 vehicles a day, help ensure a strong economy. Keeping them safe and well-maintained is essential.
The viaducts’ support structures withstood corrosion with only minor repairs through the late 1990’s. In 1998, however, a field inspection revealed extensive repairs were needed and the LifeJacket® System was sole-sourced as the only system that would meet the specification. The LifeJacket® System is a smart system that allows the current output to self-adjust to meet changes in temperature, humidity, concrete resistivity and a number of other variable factors. Installation is simple, cost-effective and minimally-invasive – all items of key importance for the owner because the project presented challenges regarding access and its effect on the economy and environment.
Skiffs or other floatation devices were rowed or maneuvered out to repair areas at high tide – the only time when the areas to be measured were within easy reach. Investigation of the lower portions of the supports took place at low tide with crews having to maneuver around treacherous rocks, debris and marine life. Measurements were taken by hand or with a laser measure. The complex geometry of the supporting columns and beams made accuracy crucial.
Throughout the project, environmental protection was critical. Not only was it important to protect all marine life on or around the structures, but also no contamination from the work was allowed. The LifeJacket® installation process was easily able to accommodate these requirements.
The largest jacket placed was 65 feet – delivered in sections. Concrete was also pumped in with the hoses threaded through the skimmer and scupper. The mixture used was very rich – about 1000 pounds of cement per cubic yard of mix – to keep it conductive with a low resistance so the current of the cathodic protection system could pass through.
Access restrictions, weather, environmental considerations and accommodating the needs of the residents and business owners – including a work stoppage during tourist season – made this project extremely challenging. Working within these constraints, over 200 LifeJackets® were placed within a twelve month period
Evaluation of the work after ten years showed that the repairs and the LifeJacket® Systems installed are performing as expected with no remedial work needed. With the success of this project determined, the second stage of the work using the same repair methods and system began in 2010.