As onshore wind turbines increase in weight and height, so too do the size of the cranes needed to construct these massive clean-energy producers. Since 2005, the average boom length of the “top out” cranes used to lift the nacelle, hub, and blades into place has increased by 25 percent, while their average weight has doubled in that timeframe.
While wind turbines are generally built on high, stable ground and include geotechnical investigation and evaluation to help ensure foundation stability, crane walks—the paths cranes traverse from one turbine to the next during construction—may cross low-lying areas or zones of weaker soils that may not be identified during an investigation. This increases the risk of cranes unexpectedly sinking into the ground or toppling.
“Knowing soil conditions along a planned crane walk can make the difference between completing your project on time and within budget or risking the safety of your project team and causing severe cost and time overruns,” said Rob Osburn, a senior geotechnical engineer at Barr.
Our geotechnical team has conducted more than 40 assessments since 2018. We help developers and contractors understand geotechnical conditions along crane walks, determine the bearing capacity of the soil, and design a crane walk suited to the larger cranes in use today.
Our work typically involves a three-phased approach—field investigation, geotechnical analysis, and graphical presentation of the results. This deliverable is then used to develop a plan for the project. The field investigation commonly consists of testing focused on areas of highest concern. Once the data is collected, we conduct a geotechnical analysis, using advanced numerical modeling to determine the capacity. The results are used to determine a factor of safety for the investigation locations along an intended crane walk.
Our GIS specialists then use the modeling results to create a map of the project area highlighting locations where barefoot crane travel is safe, where crane mats may be necessary, and potential areas to avoid.
For more information about Barr’s crane walk design and analysis services, contact Rob Osburn.
This article first appeared in the fall 2020 issue of the Barrometer, Barr's quarterly newsletter.
Photo courtesy of Charles Dana, M.A. Mortenson Company