supported by driven and drilled concrete piles were damaged to such an extent that they were condemned and subsequently demolished. Woods (2016) conduc t ed an exhumation of the foundations from a multi-story parking structure on helical piles and found no damage to the piles. These piles were later reinstalled during the rebui lding effort . In Japan, using observations from post-earthquake exhumations of damaged piles, Miura (1997) concluded that a “pile with higher rigidity will be damaged faster than a pile with lower rigidity when they are subjected to the same ground motion,” and that “[a flexible pile] is better than a pile with higher rigidity.” Unfortunately, even though there is physical proof from several earthquakes and countless success stories of flexible foundations in earthquake zones, engineers continue to design bigger and more rigid foundations. One of the reasons this may be still happening is that a good deal of confusion remains about helical pile usage in seismic areas regarding appropriate design classifications and specifications that deserve some explanation. Product Evaluation in the U.S.Helical pile design procedures in the U.S. have gone through a remarkable evolution during the past 10 years with the establishment of the 2007 AC358 Helical Pile Acceptance Criteria and inclusion of helical screw piles in the 2009 International Building Code (IBC). AC358 was written by an Ad Hoc committee of helical pile manufacturers and engineering consultants, and was presented to the International Code Council – Evaluation Services (ICC-ES). The ICC-ES is a private, for-profit evaluation company authorized by the International Building Code (IBC) to evaluate construction products. AC358 was vetted and adopted by the ICC-ES in 2007. It is used today as the basis for issuance of an evaluation report (Evaluation Service Report [ESR]) that is used to aid a building official in assessing if helical piles meet their building code (Perko, 2007). AC358 established standards for evaluating small diameter (less than 4.5 in [114 mm]), low displacement helical piles and foundation brackets, and takes into consideration the connection to structures, buckling, cor- rosion and soil interaction. The acceptance criteria include new construction, founda- tion augmentation, slab support and tension anchor product applications. It should be noted that AC358 is a product evaluation tool and not a guide code. The development of these acceptance criteria was to supplement general requirements for helical piles in the 2009 IBC. AC358 is a vehicle by which building officials can evaluate products, rate them accordingly and ensure these products meet IBC codes without requiring the pile to be engineered on every single job. However, the criteria were arbitrarily constrained by the ICC-ES to helical pile systems and devices used to support structures only in generally nonseismic areas; corresponding to Seismic Design Categories (SDC) A, B or C (AC358, Section 1.2.1) to limit the ICC-ES liability and/or responsibility as an evaluating agency. In other words, the ICC-ES established the SDC limits to “generally nonseismic” areas that would apply to its evaluation of helical piles. This arbitrary exclusion has caused much confusion within the industry, notwithstanding numerous “survival” case studies from past earthquakes in New Zealand (Woods, 2016), Japan, and the U.S. (Perko, 2009). The application and use of helical piles in areas with SDC D, E and F would require further analysis by a registered design professional. It is the responsibility of the design professional and general contractor to be sure materials used in construction meet the code for seismic applications. It is the responsibility of the building official to enforce this. Research, Education and Outreach DFI’s Helical Piles and Tiebacks Committee (HPTC) recognizes the discrepancy between the performance of helical piles during earthquakes and the professional understanding of this behavior. Recently, the committee has not only self-funded the first true seismic research study on helical piles (https://vimeo.com/177769718) to gather the necessary quantitative data, but has also compiled educational materials to disseminate to educators around the globe and for use in training webinars, which will be made available on the HPTC web page at http://www.dfi.org/commhome.asp?HLPR. For the research, the helical piles were fabricated using a 5.5 in (140 mm) diameter helical pipe with a single helix bearing plate that was 10 in (254 mm) in diameter. The helical piles were installed in dense sand in a laminar soil box on the shake table located at the testing facility at University of California San Diego (USCD). Concrete inertial weights were added to 10 helical piles to evaluate how single piles in dense sands would perform and respond under actual earthquake loads. To simulate Pile installation for large-scale shake table testing 86 • DEEP FOUNDATIONS • NOV/DEC 2017
