N.Y.C. Admin. Code § BC 1814: Section BC 1814: Helical Piles

1814.1 General.

Helical piles may be used to support axial compression, or resist axial tension and lateral loads. All helical pile foundation systems shall be approved by the commissioner in accordance with Section 28-113.2 of the Administrative Code.

1814.2 Design.

Design of helical pile foundations shall be based on a geotechnical investigation in accordance with Sections 1803 and 1810.2 with the following additional conditions stated in Sections 1814.2.1 and 1814.2.2.

Exception: For the repair of residential porches, stoops and slab on grades, helical test probes may be used to substitute for test borings, provided the helical pile has a torque to capacity ratio approved in accordance with Section 28-113.2.1 of the Administrative Code.

1814.2.1 Corrosion testing requirements.

Tests shall be performed in each soil layer for soil resistivity, soil pH, organic content and sulphate concentration. The device or system shall not be used in conditions that are indicative of a potential helical pile corrosion situation, as defined by soil resistivity less than 1,000 ohm-cm, pH less than 5.5, soils with high organic content, sulfate concentrations greater than 1,000 ppm, landfills, or mine waste.

1814.2.2 Protective treatment.

In addition to the protective treatment requirements of Section 1810.2.12, helical pile design shall consider the abrasive action inherent in the installation process when protective exterior treatment is specified as helical pile protection.

1814.3 Determination of allowable loads.

The allowable load of helical piles shall be in accordance with the applicable provisions of Section 1810.3. In addition, the requirements of this section shall apply.

1814.3.1 Allowable axial tension and compression.

The allowable axial tension and compression load shall not exceed 30 tons (267 kN).

1814.3.2 Allowable lateral load.

The allowable lateral load resisted by a helical pile shall not exceed 3 tons (29.4 kN).

1814.4 Load tests.

Load tests shall be in accordance with Sections 1810.4 and 1814.4.1 through 1814.4.4.

1814.4.1 Compression load test procedures.

The allowable axial compression load of a helical pile shall be verified by load tests in accordance with the requirements of Section 1810.4, except that ASTM D 1143 may be conducted using the Quick Load Test Loading Procedure. Following each compression load test, the helical pile being tested shall be removed by unscrewing and inspected for any deformations to the helices to verify the structural integrity of the shaft and its connections.

1814.4.1.1 Required number of axial compression load tests.

The number of axial compression load tests shall satisfy Section 1810.4.

Exception: Load tests on helical piles shall not be required, provided the following conditions are satisfied:

1. The helical pile has a torque to capacity ratio approved in accordance with Section 28-113.2.1 of the Administrative Code;

2. The torque correlation shall demonstrate a factor of safety (FS) of 2.5 on the allowable load; and

3. The maximum allowable axial compression load on the helical pile shall be 10 tons (98 kN).

1814.4.1.2 Acceptance criteria.

The allowable load on the helical pile shall be computed in accordance with Section 1810.4.1.5.

1814.4.2 Axial tension load test procedures.

The allowable axial tension load of a helical pile shall be verified by load testing in accordance with Section 1810.4 of this code; however, it shall be permitted to use the Quick Load Test Loading Procedure of ASTM D 3689. Following the tension load test, the helical pile shall be removed by unscrewing, and shall be inspected for any deformations to the helices and to verify the structural integrity of the shaft and connections.

1814.4.2.1 Required number of axial tension load tests.

The number of axial tension load tests shall satisfy Section 1810.4, but with a minimum of one test.

1814.4.3 Lateral load test procedures.

The allowable lateral load of a helical pile shall be verified with load testing in accordance with Section 1810.4. Following the lateral load test, the helical pile shall be removed by unscrewing and inspected for any deformations to the helices to verify the structural integrity of the shaft and connections.

1814.4.3.1 Required number of lateral load tests.

The number of lateral load tests shall satisfy Section 1810.4, but shall not be fewer than one test.

1814.4.3.2 Acceptance criteria.

The allowable lateral load on the helical pile shall be computed in accordance with Sections 1810.4.3.1 and 1810.4.3.2.

1814.4.4 Additional load tests.

Additional axial compression, axial tension and lateral load tests shall be performed for questionable construction as required by Section 1810.4.1.1.1.

1814.5 Minimum installation torque.

Where load tests are required, the helical pile being tested shall be used to determine the minimum required site-specific torque for installation of production helical piles. For each helical pile, the special inspector shall measure and log the installation torque for each foot of depth and the final torque in the helice's soil-bearing zone. The shaft advancement shall equal or exceed 85 percent of helix pitch per revolution at time of final torque measurement. Where load tests are not required, installation torque shall be in accordance with the exception defined under Section 1814.4.3.

1814.6 Internal stability of helical piles to resist overturning and translation.

Where bracket assemblies or structural eccentric forces cause bending, the resulting moment design of the helical pile shall ensure stability in accordance with Section 1810.2.5 and general engineering practice. Where side-mount brackets are used and a stability analysis indicates that there is insufficient internal stability to resist overturning and translation, helical piles shall be installed staggered or other means shall be designed to provide stability and prevent rotation of the foundation.

1814.7 Buckling.

When helical piles are embedded in soils of Classes 6 and 7, a buckling analysis shall be performed by a recognized method. The allowable axial compressive load shall be not more than two-thirds of the calculated load-causing buckling. The additional bending moments due to bracket assemblies, structural eccentric forces and coupling rigidity shall be appropriately included in the buckling analysis.

1814.8 Shaft flexural capacity.

Where a moment is transmitted to a single helical pile, a structural analysis shall be conducted to verify that the shaft is capable of resisting the moment with acceptable deflection.

1814.9 Side-mount bracket assembly test.

Where side-mount brackets are used, each bracket assembly shall be proof-tested to a minimum 110 percent of allowable load to demonstrate that the bracket assembly is capable of transferring the loads to the helical pile. The load shall be applied in six equal increments. The 110 percent test load shall be held for a minimum 30 minutes without bracket assembly distortion or deformation. Side-mount brackets for permanent applications shall be encased in concrete with a minimum embedment of 3 inches (76.2 mm). Concrete used to encase side-mount brackets shall meet the requirements of Sections 1903, 1904, 1905 and 1906.

1814.10 Minimum spacing of helical piles.

Minimum spacing between the center lines of helical piles shall be four times the largest helix plate diameter.

1814.11 Installation.

Equipment used for the installation of helical piles shall be as recommended by the helical pile manufacturer.

1814.12 Special inspection.

The installation of helical piles shall be subject to the special inspection requirements in Section 1705.7 and the following requirements:

1. The special inspector shall prepare a report of special inspections of helical piles and submit such report to the department in a manner acceptable to the commissioner. In addition to the requirements of Section 1705.7, this report shall also include, at a minimum, the following:

1.1 Helical pile type and product specification sheet for each helical pile installed as published by the manufacturer.

1.2 Make and model of the equipment used for installation.

1.3 Make and model number of the torque indicator used to measure installation torque.

1.4 Calibration records for the torque indicators used to install the helical piles.

1.5 The installation speed (rpm) of the helical pile.

1.6 From axial load tests and the site specific torque to capacity relationship, the minimum torque required to achieve the allowable load of the helical pile in tension or compression.

1.7 For each helical pile, the installation torque for each foot of depth and the final torque in the helice's soil-bearing zone. The shaft advancement shall equal or exceed 85 percent of helix pitch per revolution at time of final torque measurement.

2. Field welds performed in the installation of a helical pile foundation system shall additionally be subject to the special inspection requirements of Section 1705.2.