N.Y.C. Admin. Code § BC 1815: Section BC 1815: Permanent Prestressed Rock and Soil Anchors

1815.1 General.

Rock and soil anchors discussed in this document are cement grouted, prestressed tendons (bars or strands) that are installed in soil or rock. Permanent prestressed rock and soil anchors shall be designed and constructed in accordance with Sections 1815.2 through 1815.8 and PTI DC35.1.

1815.2 Additional geotechnical investigation and report requirements.

Where prestressed rock and soil anchors are used, the geotechnical investigation and report provisions of Section 1803.6 shall be expanded to include, but not be limited to, consideration of the following:

1. Recommended anchor types and capacities.

2. Suitable center-to-center spacing of anchor elements.

3. Minimum unbonded and bonded lengths of tendons, including appropriate rock or soil stratum or strata for the bond zone.

4. The effects of groundwater or voids including grout loss and reduced grout to ground bond.

5. Installation procedures.

6. Durability of anchor materials and minimum corrosion protection requirements.

7. Lock-off load and lift-off load requirements.

8. Reductions for group action, where necessary.

9. Protection of adjacent structures due to anchor installation.

1815.3 Materials.

Materials used in prestressed rock and soil anchors shall conform to the following:

1.

Bar tendons. Bar tendons shall conform to the requirements of ASTM A 722 or shall be comprised of tested materials not covered by ASTM A 722 but have mechanical properties meeting or exceeding those specified by ASTM A 722 and which have been cold stressed and stress relieved.

2.

Strand tendons. Strand tendons shall conform to the requirements of ASTM A 416 or ASTM A 882.

3.

Grout. Grout shall consist of a pumpable mixture of portland cement, water, and any required fine aggregate, supplemental cementitious materials, or admixtures as permitted by Chapter 19. Grout shall have a minimum unconfined compressive strength (f '

c

) equal to 4,000 psi (27 579 kpa).

4.

Corrosion protection. All anchors shall meet PTI DC35.1 requirements for Class I protection (Encapsulated Tendons).

1815.4 Design.

Anchors shall be designed in accordance with Sections 1815.4.1 through 1815.4.5.

1815.4.1 Ultimate bond strength.

The average ultimate bond strength along the interface between anchor grout and the ground shall be determined by a generally accepted means of analysis and confirmed by load testing performed in accordance with Section 1815.5.

1815.4.2 Applicable strata.

The bonded zone of anchors shall not be formed in soils designated as Class 6 or Class 7.

1815.4.3 Bonded zone.

The bonded zone of anchors shall be fully located within materials of similar character and strength.

1815.4.4 Group capacity.

Group capacity of anchors shall be determined by a generally accepted means of analysis and shall:

1. Ignore any contribution from soil or rock materials located beyond the property limits of the proposed structure.

2. Not exceed that of the sum of all individual anchor loads.

1815.4.5 Structural aspects.

1. Anchors design loads shall be based upon the load combinations specified in Section 1605.3.

2. Anchor design, lock-off, and test loads shall be in accordance with PTI DC35.1.

3. The cross section of the anchor tendons shall not be considered to contribute to the sliding or lateral resistance of any foundation element by means of shear friction.

4. Anchor design and lock-off loads shall consider the effects of long-term creep or changes in prestress resulting from deformation.

1815.5 Load testing.

Load testing shall be in accordance with PTI DC35.1. Extended creep tests shall be performed for any anchors designed with bonded zones located within materials designated as Class 1d, Class 4 or Class 5.

1815.6 Installation.

Installation procedures shall comply with the following:

1. Anchors shall be installed through fully cased boreholes. Open hole drilling shall only be permitted through stable bedrock.

2. Anchors having bond zones formed in soil shall be pressure grouted to at least 1.5 times the total stress at the midpoint of the bond zone.

1815.7 Grout sampling and testing.

Sampling and testing of grout shall be performed in accordance with Section 1812.1.1.2.

1815.8 Special inspection.

The installation and testing of prestressed rock and soil anchors shall be subject to special inspection in accordance with the requirements of Section 1705.19.