Acknowledgments The authors would like to acknowledge the developer, Zeckendorf; the foundation general contractor, The L’Aquila Group; the secant pile wall subcontractor, Underpinning and Foundation Skanska; the construction management team, LendLease; the architects, Robert M. Stern and SLCE; and the structural engineers, WSP; and the geotechnical and foundation engineers, Mueser Rutledge Consulting Engineers. Sitotaw Y. Fantaye, P.E., is an assoiate partner with Mueser Rutledge Consulting Engineers (MRCE). He is a registered professional engineer in New York and New Jersey and has authored or co-authored numerous papers on structural foundation design and deep foundations, including six papers published in Deep Foundations or in DFI conference proceedings. He is a recognized leader in the design of deep foundations. Michael Law, PhD, P.E., is a senior associate with MRCE. He holds a professional engineering and professional geotechnical engineering license in California. Dr. Law is an expert in underground structure behavior and computational geomechanics. 3D rendering of the support of excavation system Osterberg Load Test — The selected foundation system consisted of nominal 4 ft (1.2 m) diameter drilled shafts with rock sockets. To help optimize the design of the drilled shafts and the rock sockets for the load bearing secant pile walls, an Osterberg load test was performed in late 2013. The load test was designed such that 12 ft (3.7 m) of highly-weathered bedrock was tested. The average mobilized unit side shear of about 170 psi (1,170 kPa) was measured at the maximum load at about 2 in (51 mm) of upward movement. In addition, about 60 tsf (5,745 kPa) of end bearing was mobilized at about 0.6 in (15 mm) of settlement. Based on the test results, the allowable unit side shear and end bearing of 67 psi (462 kPa) and 30 tsf (2,870 kPa), respectively, were selected for the design. The initial design of the secant pile wall and of the lengths of the drilled shaft rock sockets were based on an assumed rock-to- shaft side friction (bond stress) allowable capacity of 100 psi (690 kPa); conse- quently, the rock socket lengths were revised based on the results of the load test. Conclusions Many challenges were faced during the design and construction of the 520 Park Avenue project including geographical constraints, difficult subsurface conditions and sensitivity of the surrounding adjacent structures. These challenges were solved with innovative design approaches, atten- tion to detail, implementation of sound construction techniques, enforcement of good quality assurance measures, and, above all, through outstanding communication and cooperation among all members of the design, engineering and construction teams. Renzo D. Verastegui, P.E., is an associate with MRCE. He is a registered professional engineer in New York. His experience includes design of support of rigid and flexible support of excavtion systems, including slurry walls and secant pile walls, design of deep foundations and design of waterfront structures. Alfredas Daugiala, P.E., is a chief engineer of Underpinning and Foundation Skanska. He is a licensed professional engineer in New York, California, Connecticut, New Jersey and Pennsylvania. He is an active member of ASCE, DFI, AISC and ACI. Daugiala is an adjunct professor at City College of New York teaching foundation engineering. DEEP FOUNDATIONS • MAR/APR 2017 • 77
