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APPENDIX 2G
GUIDELINES AND RECOMMENDATIONS
Chapter 2
Helical Foundation Systems
6. Helical bearing within soft or sensitive clays should be avoided due to long term settlement or
creep effects. Pile/anchor capacities should be limited when helix plates bear within medium stiff
clay or loose sands, and a higher factor of safety (FOS ≥ 3) may also be considered to reduce
potential long term settlement or creep.
7. Groundwater levels should be accurately identified during the geotechnical investigation,
particularly for sites with granular soils. The presence of groundwater above the anticipated
bearing depths of the helix plates may significantly reduce the effective overburden stresses,
thereby reducing pile capacities in granular soils. Groundwater table fluctuations should
be considered for the pile/anchor design and installation. The highest potential groundwater
elevation should be used for design of the helix plate configuration and the current groundwater
elevation should be used for the determination of installation torque requirements with that given
plate configuration.
8. The presence of rubble fill, construction debris, or fill soils containing cobbles or boulders should
be identified. Large, hard fractions within fill soils would likely stop advancement of the helical
pile or anchor. Pre-drilling or removal of the hard fractions may be required to allow helical piles/
anchors to penetrate these soils and reach a suitable bearing stratum.
9. When project characteristics or site conditions warrant, the Owner and his/her team of Design
Professionals may elect to determine the corrosive characteristics of the soils. Geotechnical or
environmental consultants may classify soils as corrosive based on visual review of soil samples,
from soil survey maps of the area, or from the results of additional testing. At a minimum, pH and
resistivity testing are required for a corrosion analysis. Multi-directional field resistivity testing is
preferred over laboratory resistivity testing. For a more complete corrosion analysis, chemical
analyses may be completed to determine specific concentration levels. Corrosive characteristics
of the soil should be determined from the ground surface to the bearing elevation of the deep
foundation, if practical.
10. Soil strength parameters should be determined for the top 10 feet of the soil profile when helical
piles are subjected to lateral loading. Continuous sampling or continuous in situ testing methods
should be used within this zone in order to estimate the lateral load capacity of the pile. For
critical projects, consideration could be given to special sampling and testing techniques such
as pressuremeter testing; otherwise typical sampling and testing methods as described above
may be suitable.
Alternative Methods of Developing Geotechnical Design Information
For many projects, an appropriate level of geotechnical information has not been obtained prior
to initiating a preliminary design for helical piles and push piers. New construction helical piles are
often an afterthought following a shallow geotechnical investigation and discovery of weak, near-
surface soils. Helical piles are then listed in the geotechnical report or on the project plans as a
deep foundation alternative, but additional or deeper test borings are rarely completed to adequately
identify the soil strength parameters for the deeper bearing soils. In additional to a geotechnical
investigation, there are other potential sources or methods for obtaining geotechnical information for
a preliminary design.
