CONTRACTOR SPOTLIGHT – Helical Drilling, Inc.
As one of the most experienced Ductile Iron Pile installers in the United States, Helical Drilling, Inc. (HELICAL) is a design/build geotechnical contractor located in the Boston, MA area. Helical Drilling has been providing geotechnical solutions for over 25 years – starting first with helical piles and then expanding into a wide range of grouting solutions, micropiles, excavation support and ground improvement. “We’ve been installing DIPs for more than a decade throughout the Northeast,” says Michael Cronenberger, P.E., manager of Helical’s Specialty Division, “The system is really well-suited for the varied geotechnical conditions we have around New England and fills a nice niche between our helical pile and micropile options. We’ve also seen more and more acceptance of Ductile Iron Piles within the engineering and contracting community which is helping to increase the project opportunities.” What are drivers for use of DIPs on their projects? “The speed and simplicity of installation are definitely big factors. Compared with micropiles, DIPs are much faster and easier for our crews to install.”
Please read the Project Highlight below to see Helical Drilling in action. For more information about Helical Drilling, you can also check them out at www.helicaldrilling.com.
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PROJECT HIGHLIGHT – Mass Maritime Academy
Massachusetts Maritime Academy (MMA) sits on the banks of the Cape Cod Canal in Buzzards Bay, Massachusetts. The school is the second oldest state maritime academy in the United States. In a response to the demand for student housing, the school planned construction of a 3-story, 30,700 square foot facility. Besides designing for building loads, the foundation design needed to incorporate scour effects from ocean storms.
Original plans called for the use of Pressure Injected Footings (PIFs) designed for a 50 ton working capacity. In an effort to reduce project costs and schedule, the project team led by General Contractor, Dellbrook | JKS, and Geotechnical Engineer, McPhail Associates, considered a Ductile Iron Pile alternate offered by Helical Drilling to eliminate the PIFs. The alternative approach consisted of exterior grouted Ductile Iron Piles using a Series 170/9.0 with a 270 mm (10.6-in) diameter grout shoe to construct a 10-inch diameter grouted displacement pile. The piles were designed to penetrate up to 11 feet of fill and peat/organics and terminate by bonding in medium dense to dense marine sand and gravel. The piles were designed to match the PIF capacity on a 1:1 basis to minimize any foundation changes. In addition, piles were designed to consider response to lateral loads and scour under a storm event.
Load testing to verify the Ductile Iron Pile alternative was conservatively performed in tension using a 25-foot long test pile with a 1-3/4 inch Grade 150 center bar set in the grout. The test was performed initially to the 200% design load (100 tons) where the deflection of only 0.26 inches was recorded. After rebounding, the load was incrementally increased to 150 tons (300% of the design load) to document the performance. With only 0.52 inches of deflection, the test was unloaded due to the elimination of the center bar’s structural capacity. Strain gauges installed within the pile confirmed that more than 225% of the design load was transferred below the fill and organics into the bond zone during the test indicating exceptional performance.
With the successful load test completed, the crew installed the 108 Ductile Iron Piles in 7 working days. Despite difficult driving in the dense marine sand, the DIP installation was considerably faster than the original PIF schedule. In addition, vibration monitoring around the site showed minimal vibrations which helped limit the impact on the adjacent residential neighborhood. The use of the Ductile Iron Piles provided a cost savings on the order of $300,000 and reduced the schedule by more than half the duration with PIFs.