Alle-Cat Wind Energy
Installation of 2 new greenfield substations, a new 11 circuit mile 345kv transmission line, and an underground transmission ductbank to cross an existing transmission right of way. All of this was built to support the Alle Catt Wind Energy Project, a 340 MW wind power generation facility that spanned across 3 different counties for 76 new turbines.
Challenges:
Topography
The transmission line spanned across elevations varying in over 500 feet which required multiple equipment relocations and care while traversing the right of way. This change in elevation also lends itself to varying ground conditions. Crews successfully installed foundations in running sand, bank run gravel, bedrock, and clay across the 11 mile stretch.
Soil Conditions
The soil composition on both substation sites had a high clay content requiring additional work in order to properly install. Sam and Son worked around the weather to ensure that the material’s moisture stayed within specifications. Crews worked together to utilize sheepsfoot rollers as well as traditional smooth drum rollers which helped keep the clay properly kneaded so no air pockets were created during layer installation.
Underground Ductbank
An underground transmission ductbank was required to finish connecting the overhead transmission line to the POI substation by crossing through an existing 345kv and 115kv transmission corridor. Crews installed 8” ducts with special thermal concrete in depths up to 12 feet below existing grade. Crews had to traverse a 25 foot grade change in 200 feet to cross the existing right of way. This required multiple bulk heads to prevent concrete from running down the hill and low overhead equipment in order to cross under the existing transmission lines without breaking minimum approach distances.
Highlights:
- The collection substation was built up over 18 feet on the low side. Sam and Son worked with a third party engineer to develop a retaining wall that once completed had a natural look with grass coverage around the perimeter.
- Installation of transmission foundations up to 10 feet in diameter and 52 feet deep utilizing vibratory hammers to install permanent smooth wall casings.
- The project start date was delayed 2 months and was completed on time.
