DFI 2017 Outstanding Project Award Winners In 1997, DFI established the Outstanding Project Award (OPA) to recognize the superior work performed by its members on geotechnical, deep excavation and deep foundations related projects. During the evaluation process, consideration is given to the ingenuity of the design, the construction techniques used, how the design achieved the owner’s requirements, and how the project specific geotechnical conditions and challenges were met. This year, two projects were chosen for an OPA — Berkel & Company Contractors for the renovation and rehabilitation project on the Andrew Mellon Building, a National Historic Landmark, at 1785 Massachusetts Avenue NW in Washington, D.C., and Moffatt & Nichol for its tripod suction buckets for an offshore wind turbine foundation project located off the Korean peninsula. during construction of the new basement level. To minimize differential settlement between the interior and exterior columns, 69 cased micropiles that were 7 in (178 mm) in diameter were installed prior to excavating and beneath the underpinning pits. Once the new columns and foundations were completed, load transfer to the new columns was achieved. Moffatt & Nichol: Tripod Suction Buckets for Micropile truss towers Berkel & Company Contractors: 1785 Massachusetts Avenue NW The Andrew Mellon Building is a five-story Beaux Arts-style building that was constructed in 1917. As part of the renovation, the service area of the building was expanded from 72,000 sq ft (6,690 sq m) to 100,000 sq ft (9,290 sq m) and a new basement level was added below the existing foundations. The major challenge was to transfer the load from the existing spread footings to new deep foundations, while preserving the limestone façade and plaster interiors. At each of the interior columns, a modified tieback rig was used in very limited headroom to install four micropiles each with a 100 ton (890 kN) capacity in compression. To support the exterior columns and the continuous wall footing, 55 concrete underpinning pits were con- structed and, combined with timber lagging and two levels of temporary tiebacks, were used as the excavation support system Offshore Wind Turbine Foundation As part of national offshore wind power development by the government of Korea, the construction of a 2.5 GW wind farm about 200 m (655 ft) offshore in the southwestern sea off the Korean peninsula should be complete by 2020. As part of the 80 MW pilot phase, a 3 MW 80 m (262 ft) tall offshore wind turbine was installed in late 2016, and is the first offshore wind turbine using tripod suction buckets as its foundation system. The tower foundation consists of tripod suction buckets, each cylindrical steel bucket is about 6 m (20 ft) and 12 m (40 ft) in diameter and length, respectively, and was installed in the subsurface soil deposit consisting of interbedded sand and clay layers. The design of the suction buckets followed the procedures specifically developed for very large diameter piles. Instrumentation used to monitor the installation of the suction buckets included water pressure measure- ments inside and outside of the pile, pile penetration depth into the seafloor using echo sounding and physical measurements, and inclination of the pile using two-way tilt meters. Records indicate that the entire assembly was installed with a final tilt of no more than 0.02 degrees from the vertical. Positioning at installation site DEEP FOUNDATIONS • JULY/AUG 2017 • 29
