The excavators are equipped with custom, shortened masts manufactured by HMC, so that they can safely reach multiple pylons from one location within the no-drive zones. The excavators have wide tracks with triple grousers for low impact. Their long reach and multiple degrees of freedom of the mast mean that they don’t have to drive up to each pylon like a traditional pile-driving rig would need to do. Since the drill and the vibratory hammer are interchangeable on the mast, the same make and model excavators are used for both drilling and insertion. That means they travel in the same tracks with each pass through the solar field, reducing impact to the desert even further.
The role of HYDROpro
The BrightSource Ivanpah Solar Electric Generating System has 14 excavators working on the site, and all are equipped with Trimble HYDROpro Systems. The Bechtel crews are averaging between 75 and 125 pylons per day, per machine.
The Trimble HYDROpro Construction system is used strictly for its positioning and data collection capabilities - which saved Bechtel approximately 10 to 30-minutes of surveyor time per pylon - to lay out the holes, lay out the pylons and collect the as-built data after the pylon was inserted.
“Our excavators with the HYDROpro systems provide precise XY location as well as verticality and orientation,” Wagner says. “Trimble also helped us collect Z (sea level) elevation of the top of the pylon, which is fed into and collected by HYDROpro.”
Each excavator cab is outfitted with a Trimble Tablet handheld computer running HYDROpro System software. The machines have two receivers - a Trimble SPS852 GNSS Modular Site Positioning System Receiver and a Trimble SPS552H Heading Add-on GNSS Receiver, which is designed to calculate the precise heading of the machine so that all the pylons can be oriented per specification.
Additionally, the Trimble system was instrumental because BrightSource required GPS for converting the latitude and longitude into an ECEF or Earth Center, Earth Fixed location. BrightSource uses a center of earth location in relation to the sun so that each mirror in its solar generating system is precisely aligned.