Marshall, Minnesota, June 14 -
For the first time in the wind power industry, the interior of an onshore wind tower foundation structure was inspected by remote control drone vehicle. The RUTE Foundation at Palmers Creek Wind Farm in Granite Falls, MN is a hollow foundation based on precast segmental bridge technology, which allows inspections inside the structure. Most bridge spans are made of similar box girder segments and are inspected regularly.
The RUTE Foundation was the wind industry’s first to use segmental bridge technology, and has been in operation since 2018. It won a Post-Tensioning Institute Merit Award, covered here (Marshall Independent): https://www.marshallindependent.com/news/business/2019/05/area-wind-turbine-foundation-system-wins-award/
The two previous biennial inspections of this RUTE model 32BX were performed by human confined space entry into the ‘girder cells’, similar to routine bridge inspections. RUTE’s girders, rather than being elevated like a bridge, are 12-feet below ground and stretch 30 feet in 4 cardinal directions and support a 295-ft tall GE tower. The foundation is a post-tensioned assembly of 12 precast concrete pieces. The concrete segments were manufactured at St Aubins on W College Dr in Marshall MN in August of 2018.
This year, the inspection was performed by a remote control vehicle. The components were inexpensive off the shelf equipment, including a remote control toy dune buggy, with a retrieval tether, a battery powered LED light, and Akaso EK7000 (GoPro type camera). The camera sends a video feed to the operator who sits at the ‘basement hatch’ of the GE turbine, and steers the drone via the video feed to a phone. As in prior inspections, no cracks or spalling in the girder walls was observed, indicating that the structure is performing properly.
This inspection took 1.5 hours to complete. Future inspections with custom drone equipment will take less than 30 minutes. Inspections assure the owner of the value of the structure, as well as the integrity of what is supported by the structure, in this case a several million dollar wind generator machine. The tower and generator at the top of the tower are routinely inspected.
“There is a perfect storm for modular wind tower foundations, and RUTE is in the perfect position.” said Doug Krause, President, RUTE Foundation Systems. “In 2023, the demand has grown 2-3 times to 25 gigawatts per year, compared to the last 10 years. Meanwhile steel and cement price inflation puts the RUTE BXG now in a favorable price position. Finally, the U.S. grid’s transmission lines haven’t kept up with the demand for clean electricity. As a result, wind farms are trending to very large project sizes in more remote areas, consisting of hundreds of towers along with dedicated transmission wires. For RUTE, this means a job with hundreds of foundations defrays the set-up cost of the mobile precast factory, which makes the RUTE BXG the lower cost foundation solution. Next, RUTE plans to build new mobile precast equipment in Marshall, MN, led by Bob St Aubin. The equipment includes high strength concrete temperature controls and robotic features in order to produce one foundation per day in remote regions. The demonstration of the mobile operation will continue our Marshall, MN operation’s series of wind-industry-first innovations.
About RUTE Foundation Systems, Inc.:
RUTE Foundations use 50% less concrete, and 25% less steel than a conventional poured-in-place ‘spread’ foundation. Founded in Oregon in 2015, with an operations hub in Marshall, MN since 2018, RUTE manufactures and sells modular structures that support wind and solar generators. Namely, the RUTE BXG for wind towers, and the RUTE SunTracker for high clearance solar power for cattle pastures.
About Box Girder Bridge Inspection:
Picture 1. Box girder bridge segment being craned into position. RUTE Foundations flip the segments the other way around; the long ‘wing’ is face down, pushing on the ground.
Picture 2. Inside of a completed segmental bridge. The inside is called the ‘cell’. The concrete walls are thin and designed not to crack. Concrete condition inspections look for cracks in the walls or ‘spalling’ (e.g. cracks by the joints). The absence of cracks indicates the structure is behaving as designed.
Picture 3. Inside the RUTE Foundation Core. Image by remote control tethered vehicle. Coordinate image is drawn on by hand after the inspection. The Aluminum cover was fabricated at BendRite in Marshall, MN in 2018 and appears in good condition as do the concrete walls of the foundation.