Technical Manual

Inc.

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APPENDIX 2G

GUIDELINES AND RECOMMENDATIONS

Chapter 2

Helical Foundation Systems

1. Establish a relationship with a local geotechnical engineering firm. An established, local

geotechnical firm may have performed a previous investigation within the area of the proposed

project, or have knowledge of the general soil profile. A discussion with the geotechnical firm

would allow the installing contractor to, at a minimum, determine if soil conditions are suitable

for use of helical piles or push piers.

2. Contact local well drilling firms for any information regarding local ground/geologic conditions.

3. Contact the Geologic Survey for the applicable State jurisdiction. This agency often maintains

records of test borings and wells throughout a given state, and this information may be used to

support a preliminary design effort.

4. Conduct a test installation of a helical pile/anchor, also called a “helical test probe”. A typical helical

test probe consists of a Model HA150 or Model HA175 lead section with a single 10 or 12-inch

helix plate and multiple extensions to reach the required depth. For some soil profiles, a double

helix may be necessary to provide the thrust needed to penetrate stiff or dense strata or advance

through particularly soft zones. For these situations, a double 8/10 or 10/12 helix configuration

generally works well. Torque must be monitored in one foot intervals during installation of the

test probe(s) from the ground surface to the termination depth. The torque readings must be

taken with calibrated equipment such as a certified gear motor and calibrated pressure gages or

by using a calibrated torque transducer in line with the drive tooling. The depth of investigation

would be similar to that described above; i.e., 5 to 10 feet below the anticipated depth of the

production piles. A general understanding of the soil profile and depth to groundwater may be

required to back-calculate soil strength from a helical test probe. The proposed number of helical

test probes for a given project is dependent upon the project characteristics and the variability

of site soil conditions. Factors of safety greater than 2.0 must be considered when the helical

pile/anchor design is based solely or in large part on the results of helical test probes. The

following information is required when evaluating the results of helical test probes: make and

model of the gear motor, calibrated torque readings, test probe shaft size, and test probe helix

plate configuration. For push pier projects, the installation of a test push pier typically provides

sufficient information for a push pier preliminary design.

5. Performa load test. If site access allows the setup of a load test frame, the results fromcompression

or tension load tests can determine helical pile or anchor capacity without soil information. The

required number of load tests would again be dependent upon project characteristics and should

be determined by design professionals. The helical piles or anchors used for the load test(s) shall

be installed with calibrated equipment so the true installation torque is known. The load tests

should be performed in general accordance with applicable ASTM standards. A site-specific

torque correlation factor can be determined from the results of the load test(s), which would then

allow the final installation torque readings to be used for pile capacity verification.

Helical piles, helical anchors and hydraulically-driven push piers are installed routinely on residential

projects without adequate site-specific soil information available. The homeowner is often unwilling

to pay for deep soil borings, laboratory tests and recommendations from a geotechnical consultant.

In these cases, the installing contractor typically proposes a specific pile or anchor system with

depth/length and product spacing based upon experience from doing previous work in the area. The

contractor then follows rules-of-thumb guidelines for installation.

FSI offers a software tool called “Foundation View” to assist FSI installing contractors in estimating

structural residential loads and spacing of retrofit piers. This program assumes that the soils are