Construction is underway at a new, five-story apartment complex situated in Boston’s historic Fenway Park neighborhood. DuroTerra’s End-Bearing Ductile Iron Piles were installed by Helical Drilling to successfully support heavy building loads with minimal vibration.
Ductile Iron Piles were carefully evaluated against conventional pile technologies and proved to be the most advantageous solution. With loads approaching 600 kips, deep foundation support was required at the fill/soft soil site. The project team initially considered driven steel helical piles with 100 ton capacities. High vibrations coupled with the challenges of transporting long pile sections in an urban setting and the added cost/time for pile splicing led the design team towards a more practical solution for the urban site. Ductile Iron Piles were selected as the most cost-effective and fastest alternative to Helical piles and traditional drilled micropiles. The Ductile Iron Pile system provided a 2:1 replacement of Helical piles, along with a working capacity of 50 tons.
The site, only three blocks away from Fenway Park, is situated in an extremely congested area, surrounded by existing three-story residential complexes. The soil conditions consisted of up to 9 feet of loose to medium dense “urban” san fill underlain by soft peat and organic clay/silt to 28 feet. The fill and organics were underlain by very soft to medium stiff clay extending to a depth of 175 feet where bedrock was encountered
Prior to the start of production operations, Helical Drilling installed the 50 ton test pile (Series 118/7.5) to terminate on rock at a depth of 175 feet. The test pile was loaded using a gravity reaction load test setup because of the costs associated with deep rock anchors for tension resistance. Load testing of the End-Bearing Ductile Iron Piles showed a deflection of 1.25 inches at the design load (100%) of 50 tons. The load test was performed to 200% of the design load (100 tons). The response was nearly perfectly elastic with a deflection at the maximum test load approaching 3 inches. The deflection of the 175-ft long test pile met expectations for compression of a long micropile. The results met the project teams expectations while also delivering foundation economy.
Production pile installation was performed at rates of 1,000 feet per day or more. A total of 87 piles were installed in just over 2 weeks. Vibration monitoring performed during installation recorded peak particle velocities of only 0.3 inches/second on the ground 2 feet away from installations. The vibrations were reduced to 0.15 inches/second a distance of 4 feet away. Measurements on the existing building foundations were less than 0.15 inches/second while installations were within 2 feet from the building.
Project Team Members
DIP Design/Build Partner: Helical Drilling, Inc.
Geotechnical Engineer: Briggs Engineering
General Contractor: Boston Design Construction
Structural Engineer: DM Berg Consultants, P.C.
Architect: Nunes Trabucco Architects