Mon, February 1, 2021 – Southeast Edition
UMA worked in two shifts to install more than 300 micropiles to support a manufacturing facility addition for a global manufacturer in Goose Creek, SC
Specialized subcontractors such as UMA Geotechnical Construction Inc. (UMA) rarely gets credit, but the work they do often lays the foundation for stimulating the global supply chain. The North Carolina-based contractor worked two shifts to install more than 300 micropiles to support a manufacturing facility addition for a manufacturer in Goose Creek, SC
Exclusive bidding process
The UMA team overcame adversity by acquiring the project through a high pressure process called the Japanese reverse auction. Although common abroad, this was new territory for a geotechnical contractor serving the United States’ Central Atlantic.
The first step was for all interested contractors to send a proposal via email to the owner. The owner then posted the highest bid on the Internet for all to see. The Japanese Auction leaves bidders blind, so the UMA Team had no information about the other bidders.
Every minute, the bid would fall by $ 10,000 and bidders would be asked if they were willing to accept that number. As soon as they confirm, the timer will be restarted before the price is lowered again. This process was repeated until the lowest possible bid was reached.
UMA had to determine how low she was willing to go.
“Our approach was to pre-determine our lowest number,” said UMA President Brian DeSpain. “After discovering the bidding process, we went back to our estimate sheet and creatively found the most economical and productive route to install the piles.”
Installing two-phase micropiles
UMA ended up securing two of the three phases of the addition in November 2019, including an addition to the manufacturing building (Building F) and an expansion to accommodate the huge turntables used by the manufacturing unit (Building J).
Among the complexities of the project was the large volume of micropiles to be installed – 304 to be exact. The first phase, Building F, contained 290 piles, and Building J contained 14.
Team UMA arrived at the site during Christmas 2019. The first test stack was installed in late December and tested in January. Two load tests were conducted at 480 kips. UMA designed piles to reach loads of 240 kips for Building J and 200 and 240 kips for Building F.
UMA started production shortly thereafter, installing (or drilling) more than 20 piles a day and working in two shifts. The work was completed before the February deadline. Once the micropiles in Building F were completed, UMA left for a month before returning to finish the 14 stakes in Building J.
True Design-Build
UMA was initially provided with a Terracon geotechnical report based in Charleston, SC. Although meticulous, geotechnical surveys are only guaranteed with precision when drilling. The distance between the polls can vary, as can the characteristics of the soil.
“They basically said, here’s the geotechnical report and the spacing that we want to try to use,” said DeSpain. “Our job was to find out the diameter, depth and the means and methods used to install the piles.
UMA worked with general contractor Fessler & Bowman Inc. and the owner’s engineer to select a deep base system designed and built to meet your needs. The selection was a 7 inch outer diameter (OD) casing. The coating was installed over the entire length of the micropile for structural capacity and the connection zone was injected under pressure through the coating. A 14 by 14 by 2 in. Plate It was fixed to the top of each pile with a non-structural bar and nut and embedded in the structural concrete slab.
The UMA team placed the micropiles 6 meters apart and in a perfectly aligned grid pattern. Fessler & Bowman continued to launch a multi-layer reinforcement slab for the foundation.
“With a perforated coffin or pier, you would assume a final supporting pressure at the bottom and then you could also use the frictional force between the mortar and the soil,” said DeSpain. “With micropiles, the design standard for final load capacity is zero, so you strictly rely on the friction between the mortar and the soil.”
UMA’s design-building skills were tested unexpectedly when its work was more than half completed. The contractor was informed that four additional columns in the middle of the building would need support.
“They made us add four microcells to each of the four columns,” said DeSpain. “We continued construction, made a project and approved it, and then implemented the new project while we were on the spot without delay.”
Specialized Drilling Equipment
UMA used one of its specialty Casagrande C7 XP-2 drilling platforms for all micropile drilling. He worked in conjunction with an excavator with an EZ Spot UR attachment, which fed the coating sections to the platform.
A positive displacement pump supplied water to the C7 during drilling to wash the coating sections to depth. The advantage of this pump was that it provided a constant flow and pressure of fluid throughout the process.
UMA’s goal was to use the longest possible steel sections. The C7 is equipped with a 30-foot engine. course so the team could install a 30 foot. section for the first piece, followed by two 25-foot pieces. Sections.
UMA used a Penndrill cement silo to reduce labor and increase production. Positioning it above the mortar plant allowed the cement to be loaded directly from the truck to the silo, without breaking and dumping each bag.
Drilling through Cooper Marl
After penetrating a layer of black silty organic sand, UMA was drilling through Cooper Marl, which is a soil formation prevalent in the Lowcountry region of South Carolina along the coast. The contractor is no stranger to drilling in this material.
“Seashells, organic matter and sand accumulate on top of each other and compact more and more over millions of years, and formed this really dense layer of sand that is commonly known as Cooper Marl,” explained DeSpain. “It’s interesting when you drill because this mixture of material from millions of years ago comes from the ground.”
The connection zone for the micropiles fell within the Cooper Marl layer. UMA drilled the piles at an average depth of 21 meters, although it floated because the layer was 50 meters on one side of the site and 25 meters on the other section.
The Cooper Marl acts as a degraded rock during drilling, so the hole will remain open. The wet sandy cover layer above; however, it collapses in the hole. This required UMA to play in the OCI Division of Global Drilling Supply in Brookville, Pennsylvania, to make a special drill that it has used several times since 2011. OCI also supplied the entire housing for the project.
UMA worked closely with the OCI on the drill size. The length that the cutting teeth designed from the casing was critical to ensure that the drill’s outside diameter was greater than that of the casing. This dimension was critical to ensure that the drilling fragments and cuttings returned to the surface effectively; the wrapper was not stuck in the sand by friction; and the mortar could completely encapsulate the coating.
“When you drill below the water table, the pressure needed to overcome the hydrostatic pressure increases by approximately one atmosphere every 33 feet,” said DeSpain. “You want to be able to push the fluid out of the bit, but you don’t want the fluid or cuts to come back into the bit. This bit just lets the water out, allowing us to wash the cuts out of the tube back to the surface. “
Fessler & Bowman covered the entire site with a mud mat before UMA started the drilling rig. This was basically a concrete slab to serve as a stable work platform in this muddy location.
The sediment removed by the drilling rig accumulated on the belt as the drill cuttings were expelled from the hole. UMA implanted a skid steer loader to remove waste from the conveyor and put it in a pile where Fessler & Bowman allowed it to dry before removing it from the site.
The UMA team worked from the inside out of these U-shaped plots. “When we reached halfway, Fessler & Bowman came in and blocked half the package and started to tie up all the rebar cages,” said DeSpain. “They had already poured the first half of the concrete around the same time that we finished drilling the last pile.”
When all was said and done, UMA had completed 304 micropiles by the February 2019 deadline. The UMA team was required to work in two shifts, deploying its fleet of special foundation equipment and its previous success working with the Cooper Marl formation. The result was a solid foundation that would allow this global manufacturer to increase production and further stimulate the economy.
“The key to this work was to install many micropiles at a high production rate,” said DeSpain. “The owner had a very strict schedule and Team UMA took care of it.”
