It feels like an exaggeration to say it out loud — "20 million cubic yards of dirt and rock will be moved."
But Ryan Lepke, GPS site coordinator for Sukut Construction, Inc., Santa Ana, Calif., doesn’t flinch a bit when describing the massive Three Oaks at Walnut Hills subdivision grading project that his GPS grade checkers worked on in Walnut, Calif. just outside of Los Angeles. Transforming the 550-acre, hillside site into a 268-home subdivision of prime lots with panoramic views of metropolitan Los Angeles had been a definite challenge.
"Land is at a premium in southern California," Lepke, states. "All the easy parcels of land in the area have been developed, so we’re building a site that requires a little imagination."
"Requires a little imagination" may be a polite way of describing huge geological issues, which include ancient landslides that require removal of a couple million cubic yards of bedrock at each of eight major shear keys and dozens of buttresses. A shear key or shear zone refers to the shearing of rock being at the edges of tectonic plates. Challenges include 280-foot vertical drops from building pads measuring 100- by 200-feet with 1:1 slopes descending to natural ground.
Digital Site Plan Imperative
"With the rugged terrain, and its corresponding deep slopes and extreme angles, it was essential to us that we utilize a 3D digital site plan that could be plugged into our GPS-guided equipment," said Matt Eklund, GPS program manager with Sukut Construction.
Sukut wanted complete quality control management on the project so the company built its own 3D site model. "Because we created the 3D digital models ourselves, we were able to complete a constructability analysis of the engineer’s plans, which means we were able to flush out the impurities and fix any plan inconsistencies well before a dozer blade touched the ground," Eklund said.
Any inconsistencies found in the engineer’s site plan involved vertical and horizontal alignments not fitting as drawn in plan view. Eklund explained, "When you look at the site plan in 3D, you can see right away where things are not going to fit. With a conventional site plan, the surveyor might survey a 2:1 slope when it actually should be a 2.1:1 slope — so, you can see that being off a small amount can propagate throughout the project and create problems or wasted time and materials. Therefore, by taking a look at the project as a whole in a 3D plan you can tie everything together ahead of time."
To achieve the steep slopes and to create the building pads, as well as what will be city-maintained streets and parks, Sukut used large equipment such as a Caterpillar D10T Track-type Tractor equipped with the GPS-based Trimble® GCS900 3D Grade Control System.
"Stakeless Perfect Grade"
"The Trimble GPS machine control has enabled us to complete the work accurately with 75% fewer stakes," Eklund said. "Being able to bring down these huge shear keys that have anywhere from one to two million cubic yards of bedrock safely without a grade checker or survey wood and to maintain perfect grade all the way down is truly remarkable and has sped up the job."
"If we had used traditional methods to build this project, we would have had two full time survey crews, plus additional grade checkers to work with those stakes. Equipping the dozers with GPS and empowering our grade checkers with the ability to do their own layout, allowed us to add an extra spread of scrapers and cut the schedule by five months."
The developer of the Three Oaks at Walnut Hills subdivision is Standard Pacific Homes, a large national developer that got its start in the mid 1960’s. Standard Pacific has designed the project to be totally high-end. Three different residential design concepts are planned with 10 different floor plans ranging in size from approximately 3,250 to 5,000 square feet of living area.
"When I first saw the site and was told what our plans were…. my reaction, after I caught my breath, was wow," states Tony Freitas, senior construction manager with Standard Pacific Homes.
Developer’s High Expectations Exceeded
"We took some risk going with a contractor who made promises based on GPS 3D machine control, but Sukut and the Trimble system have simplified my life," Freitas said. "I don’t have to schedule surveyors to be out there pounding points. And then, if something is missing, people aren’t coming to me and then I’m going back to the engineers, and then we go back and forth, and back and forth. Sukut takes care of everything.’
Eklund added, ’We experienced very little rework on this project and were able to avoid potential cost over runs with a great deal of credit being given to our GPS site coordinator Ryan Lepke and the use of Trimble GPS equipment."
"Sukut is completing the project on a timeline that’s much quicker than we ever anticipated," Freitas said. "They’ve shaved about five months off the schedule, which means we’ll be building homes that much sooner. I wish all my subcontractors were performing like Sukut."
"When you consider the massive amount of soil to be moved, the 450- to 500-foot vertical elevation changes, multiple canyons and a huge ridge line that splits the site in half, this project is its own animal," Freitas said. "It would have been very difficult for a subcontractor to tackle these complexities without GPS machine control."