You need to build a stable foundation for improvements to a pump station but you’re located in a five-foot water table within proximity to a creek. How do you keep the foundation from rising? One Georgia county’s engineer chose to pin it down with rock anchors and UMA Geotechnical Construction was the right fit for the job. “The rock anchors are there for when the structure is empty,” explains UMA’s Senior Engineer/Estimating Manager Mitch Crayton. “When it’s empty and the ground water table is above the bottom of the structure, if the rock anchors aren't there, it could push up out of the ground like a boat. These buoyant forces are exactly what the rock anchors are there to resist.” Cherokee County Water and Sewerage Authority outsourced this pump station improvement project to Atlanta-based Lakeshore Engineering, a heavy civil contractor that focuses on industrial, municipal, and en- vironmental projects. UMA served as the geotechnical subcontractor. Located within proximity to Blankets Creek in Canton, Georgia, the water table is known to fluctuate. UMA’s sole function was to install a rock anchor system to keep the pump station’s concrete slab pinned down. The components to be built on top of the slab would be a diesel engine-driven centrifugal pump and a concrete cast-in-place emer- gency storage tank. Working Down in the Hole One of the biggest challenges for UMA’s team was working in a 23-foot-deep-by-56-foot-wide excavation. Lakeshore Engineering had excavated the pit and installed a soldier pile wall with wood lagging. Tied off workers accessed the pit via ladders. “We're working in a pretty tight area compared to what we're normally used to on highway projects,” says Crayton. “It's not the smallest footprint we’ve worked in, but it's a lot smaller than our usual working space.” Lakeshore Engineering installed a mud mat to provide a stable working surface for UMA’s drilling rig and to keep the work site clean. There was no air movement so air was pumped in from ground level and circulated with fans to keep workers from breathing in diesel fumes. The working area had to be dewatered also due to the proximity of Blankets Creek and a water table approximately five feet below the ground. While the failure of dewatering pumps would not have been cataclysmic, the potential slow accumulation of water in the working area could have damaged equipment. UMA Goes Deep to Anchor Georgia Pump Station By Brian M. Fraley
UMA’s team worked in a 23-foot-deep-by-56-foot-wide excavation to install rock anchors at the Blankets Creek Pump Station.
One of the visual spectacles on the project was Lakeshore Engineering using a crane with rigging to lower a Beretta T46 Drilling Rig into the excavation as UMA’s team provided direction. “It's a smaller machine, but we selected it for this purpose,” Crayton explains. “It doesn't quite get the production that we're typically used to, but it can hold its own with this smaller hole size.” UMA’s crew was seasoned and used to working together. They were also familiar with the equipment and how to rig it based on past proj- ects. “We shut down around Christmas every year for safety and for training,” Crayton says. “We alternate between first aid, forklift certi - fication, and crane and rigging so that everyone is safe on the job site. That's always our number one concern.” Drilling the Rock Anchors UMA was tasked with installing 24 rock anchors, evenly spaced ev - ery 10 feet vertically and 8 feet 8 inches horizontally. Skyline Steel supplied the anchors, which were 1-inch-diameter Grade 150 ksi DCP (double corrosion protected) bar. The owner’s representatives provided
Prime contractor Lakeshore Engineering used a crane with rigging to lower the Beretta T46 Drilling Rig into the excavation as UMA’s team provided direction.
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DECEMBER 2021 csengineermag.com
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