Buesing Corporation brings a world of specialty construction experience to projects in and around the Phoenix area, tackling everything from mass excavation to shoring and drilling to installation of solar panels. In that last area, Buesing has been particularly prolific, having installed nearly 640,000 piers for solar panel work alone. The company has been a long-time GNSS proponent, regularly using many variations of the solution in its projects, and brought that expertise to bear on a recent landfill capping project that could have been a survey stake nightmare. Instead, using a fleet of machines running GNSS-based machine control, Buesing has cruised through the first four phases of the massive job and is poised to start the fifth and final phase in 2017, which will close the fill.
No Longer the Pits
The push toward a recycling-focused society, which started in the "˜70s, was driven as much by a growing shortage of disposal space as it was by a sense of moral or ethical responsibility. Landfills, once thought to be inexhaustible in both volume and supply, were quickly reaching capacity and the NIMBY (Not In My Back Yard) movement was hindering the establishment of new ones. Action was taken to pre-sort material prior to landfilling, resulting in a number of different classifications of fills. According to Doug Diemer, Director at Waste Management, Phoenix, a parcel of land that was owned by the state and leased to a sand and gravel company would become one such landfill.
"When the sand pit became depleted of its material in the 1980s, the land was returned to the state's ownership and subsequently made available for use as a landfill," said Diemer. "It was leased by Waste Management, named the Lone Cactus Landfill and was designated for use as a construction and demolition (C&D) debris landfill. Unlike a traditional landfill which can take in municipal solid waste (trash, food wastes, etc.) from the general public, Lone Cactus accepted only inert material generated during the construction, demolition and renovation of structures - material such as concrete, asphalt, brick, wood, metals, glass, insulation, sheetrock and more."
The landfill operated continuously from the "˜80s through May 2013 when it finally reached capacity. According to Diemer, the site, which was once a deep pit on North 7th Street, now towered some five to six stories above grade.
"Our records show there is more than 10 million tons of C&D debris buried at Lone Cactus," he said. "We closed the operation - shifting deliveries to other areas C&D fills - and began the process to cap the landfill."
Inert the Media
Capping a landfill is done to ensure the material contained within remains in place and, in some instances, to allow for subsequent development of the land. In a traditional landfill, the capping process can be extremely elaborate due to the nature of the material contained within. Decaying organics can leach into groundwater systems and emit methane gas, which must be vented off. At Lone Cactus, however, since all the landfilled material is inert in nature, the cap is much more straightforward, according to Dan Kuehl, Project Manager for Buesing, general contractor on the project.
"Though the project was broken up into five separate phases to better accommodate for its size - almost 200 acres - each phase is essentially identical in approach," he said. "When we first get onsite, we clear and grub the side slopes, survey them and put down three compacted lifts of soil to equal 18-inches of material, and then top that off with 3-inches of rock."
The approach to the top deck differs a bit, given that Buesing has to achieve a minimum of a 3 percent slope from the crown to the hinge points to assist in drainage. Once they've graded and achieved that slope, they survey it, and it becomes the foundation layer for the actual capping.
"At that point, we bring in material and continually build up a barrier layer in three compacted lifts, until we have a depth of 18 inches on the top deck as well," he said. "We then fine grade that barrier layer, survey it and top it with 6-inches of an AB grade (less than 1-inch) stone. That material is then compacted, graded and surveyed to form what's called the erosion layer."
The volumes of material with which Buesing is dealing throughout the five phases of the Lone Cactus project are impressive indeed. By completion, the company will have placed 58,000 tons of armor rock (1-inch to 3 inches); 245,000 tons of AB rock; and a whopping 500,000 cubic yards of specialty soil used to form the barrier layer.
Because the Lone Cactus project was so grading-intensive - multiple lifts on both the side slopes and top deck - Buesing chose to bypass traditional construction staking and instead rely upon the machine control capability that has served them so well in the past.
"It was definitely the way to go," Kuehl said. "We hit a bit of a snag on Phase 1 when the engineer working for the owner felt that we should design the top deck ourselves. That demanded a lot of trial-and-error and was not the most efficient way to get the job done. Once the engineer took control of that part of the job, however, it was a simple matter of bringing her CAD files into our computers, doing our cut/fill maps and then populating that info and data into a model for our machines and rovers. In that way, we have the option of building one model and dialing up on the Topcon system, or building the model for finished grade and dialing down to it. It was huge savings."
For the Lone Cactus job, Buesing is using a John Deere 850K Dozer and a pair of Caterpillar 140M Motor Graders, all equipped with Topcon 3D-MC2 systems purchased through Gilbert, Arizona-based Branco Machinery. Kuehl said the dozer - equipped with a slope board to aid with spreading of the rock armor - is dedicated strictly to working the side slopes, while the graders work the top.
"We have one of the graders outfitted with a single mast and the other using a dual-mast configuration," said Kuehl. "The single mast machine is serving as a knock-down blade, essentially taking down material from the bottom dumps and getting it close to grade. The dual mast unit comes behind him and is able to get material to our self-imposed tight tolerances."
Kuehl added that the project is actually only demanding compliance to the standard construction spec, which is about .1 of a foot. But, again, the size of the job site dictated otherwise for them. "On a site like this - even just a single phase of it - .1 of excess material over 40-plus acres could be pretty substantial. So using Topcon 3D-MC2 with the dual mast, we keep things much tighter than that. In fact about .05 is what my surveys come back at. The fact that we are able to dial it in that closely is really paying off for us."
Creating a Diversion
With both the barrier and erosion layers in place atop the fill, Buesing then constructs a series of diversion berms that measure 2.5 feet high, 4-foot across the top with a 4:1 slope. These berms direct any collected water to a series of pipes that carry it down the slope to a channel that encircles the landfill.
"Once it is in the channel, it is then routed to one of several sediment basins that we built," says Kuehl. "GNSS played a big role in those areas as well, keeping costs down by not having to stake each part. This job was as good a fit for machine control as you can get. Without it, we would have had to stake each lift of the barrier layer, then stake the erosion layer, and then stake the channel and ponds. It's tough to quantify exactly, but I'd have to say we're saving about $1,000 per acre using the Topcon solution. So, on a project of this size, it's easy to see why we're so pro-machine control."
The Lone Cactus Landfill project is slated for a 2017 completion.
Our newsletter right to your inbox.
See stories from other regions.