American Construction & Engineering, Bartow, Fla., is currently working on a gypsum stack expansion for the Mosaic Company.
Keith Cook was the supervisor on the job site, and explained that his crew handled the expansion to allow Mosaic to continue mining phosphate.
“It was a complex process,” Cook said. “At the beginning, we had to strip away the vegetation for the footprint of the gypsum stack expansion. That was done by another contractor, and then once they finished up, then we came in and established borrow pits. Then from that point, we established haul roads utilizing the material.”
Cook said that one of the borrow pits covered a four-acre area, while the other was about six acres. They went down at least 67 ft. (20.4 m), using mostly excavators, long reach excavators, and 40-ton (36.3 t) Volvo haul trucks. For this project, there were a total of 23 trucks and multiple excavators in each borrow pit.
“What happened when we were excavating that material is that it was too wet,” Cook said. “To utilize it, it has to be at the optimum moisture content, so what we did was dig the material and flip it. For some of the excavators, that’s all they did for 10 or 12 hours a day, was aerate the material. Then we’d get to certain areas where the material was too dry, and we had to hydrate it. We had ditches that were established that would convey water to the area that had the dry material. We blocked it in, mixed it up all together, and let it hydrate.”
A little over a million cu. yds. was taken out of the borrow pits, and depending on the pit, the haul was approximately 2 mi.
“We had the short stick excavators, which dug down approximately 18 feet,” Cook said. “They would dig as deep as they could to get a ditch deep enough, so they could start so the gypsum would bleed out and start to dry out. Once that excavator made that cut, the long reach would then pull that slope — we still had to maintain a three to one slope from off the side of the gypsum stack. So the long reach, that’s basically what he did — he came back and cut the slopes, or he’d come back and clean out the ditches at that time. Once they made that cut to dry out the borrow pit, they would then make another cut flipping that material, so he would dig down maybe 20 feet, but then another excavator came behind him digging down maybe 15 feet and breaking that material up.”
Cook said that they couldn’t excavate the ballast trenches until they had the gypsum beside them.
“We couldn’t get equipment down on top, so we had to push a pad out with gypsum and excavate the ballast trench,” Cook said. “Everything had to be done in a timely manner, because there was another company there to repair the liner that was in the ballast, because of damage from gophers, so they would replace the liner in each ballast. We had to go quickly to get them access to it, because of the timeline for them to repair it, and for us to finish pushing that area. It was kind of like a dancing relationship. If they slowed down, it would slow us down, and if we slowed down, it would slow them down.”
Equipment for the job included four Cat D6N GPS-ready dozers and Cat D6T dozers. Trucks and excavators were mostly Volvo, but included a few Caterpillars and John Deeres. There were a total of 23 trucks and nine excavators.
“ACE and Flagler have established a relationship over the years built on trust and common goals,” said Chad Hastings, account manager of Flagler Construction Equipment. “ It was through this relationship that Flagler was able to supply ACE with 25-plus Volvo A40F’s and six Volvo EC480D’s to efficiently tackle the job on hand. By working together, we were able to optimize production and successfully complete the project. Through these successes, that relationship continues to grow stronger.”
Cook said that moisture control was one of the biggest challenges with the project.
“It’s not like a science where you get the moisture right, because the material changes with gypsum,” Cook said. “All gypsum is not the same consistency. Some might have a little bit more sand in it, so where you would find your moisture is based on that proctor curve. So if we had an area that failed compaction, I needed to know what the moisture was in that material. So if you tell me the moisture is an 18, and optimum moisture is 13, it’s too wet. So then I would have to come in and cut out about six inches of it, and I would take a vibratory roller and put it on top of it and just pound it and pound it to bring the water up on top to the surface. Once the water was at the surface, I’d trim it off and we would generally get our compaction that way. So the moisture in the material was like the key element in that job.”
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