N.Y.C. Admin. Code § BC 1810: Section BC 1810: Deep Foundations

1810.1 Scope.

Deep foundation elements, including but not limited to timber piles, precast concrete piles, structural steel piles, cast-in-place concrete piles, caisson piles, drilled displacement piles, composite piles, and helical piles, shall comply with Section 1810; driven piles shall comply with Section 1811; cast-in-place concrete piles shall comply with Section 1812; composite piles shall comply with Section 1813; and helical piles shall comply with Section 1814.

1810.2 Deep foundations – general requirements.

1810.2.1 General.

Deep foundations shall be designed and installed in accordance with the requirements of the geotechnical investigation and report required by Section 1803 and Sections 1810 through 1814.

1810.2.2 Additional geotechnical investigation and report requirements.

Where deep foundations are used, the geotechnical investigation and report provisions of Section 1803 shall be expanded to include, but not be limited to, consideration of the following:

1. Recommended deep foundation types and their capacities.

2. Designation of bearing stratum or strata.

3. Suitable center-to-center spacing of deep foundation elements.

4. Reductions for group action, where necessary.

5. Load test requirements.

6. Durability of pile materials.

7. Installation procedures.

8. Protection of adjacent structures due to installation.

9. Field inspection and reporting procedures (to include procedures for verification of the installed bearing capacity where required).

1810.2.3 Special inspection.

Special inspections for deep foundations shall be performed by an engineer in accordance with Sections 1705.7 and 1705.19.

1810.2.4 Pile caps.

Pile caps shall be of reinforced concrete, and shall include all elements to which deep foundations are connected, including grade beams and mats. The soil immediately below the pile cap shall not be considered as carrying any vertical load. The tops of deep foundations shall be embedded not fewer than 3 inches (76.2 mm) into pile caps and the caps shall extend at least 4 inches (101.6 mm) beyond the outermost edges of the deep foundation elements. The tops of deep foundations shall be cut back to sound material before capping. Pile caps shall be protected from the effects of frost in accordance with Section 1809.3.1.

1810.2.5 More than one type, capacity or method of installation for deep foundations.

In the conditions described below, the several parts of the building supported on the different types or different capacities of deep foundations shall be separated by suitable joints providing for differential movement, or analysis shall be prepared by the engineer, establishing to the satisfaction of the commissioner that the proposed construction is adequate and safe, and showing that the probable settlements and differential settlements to be expected will be tolerable to the structure and not result in instability of the building.

The load test requirements of Section 1810.4 shall apply separately and distinctly to each deep foundation type, capacity, or method of installation, except where analysis of the probable, comparative behavior of the different type or capacity of the deep foundation or the method of installation indicates that data on one type or capacity of deep foundation permit a reliable extrapolation of the probable behavior of other types or capacities of deep foundations. The requirements of this section apply to the following proposed conditions:

1. Construction of a foundation for a building incorporating more than one type or capacity of deep foundations;

2. Modification of an existing foundation by the addition of deep foundations differing from the type or capacity used in the existing foundation;

3. Construction or modification of a foundation utilizing different methods or more than one method of installation, or using different types or capacities of equipment (such as different types of hammers having markedly different striking energies or speeds); or

4. Support of part of a building on deep foundations and part on shallow foundations.

1810.2.6 Settlement analysis.

The settlement of an individual deep foundation or groups of deep foundations shall be estimated based on approved methods of analysis. The predicted settlement shall cause neither harmful distortion of, nor instability in, the structure, nor cause any stresses to exceed allowable values.

1810.2.7 Use of existing deep foundations.

Deep foundations left in place where a structure has been demolished shall not be used for the support of new construction unless the existing deep foundations are load tested in accordance with Section 1810.4, original installation and testing records of the existing deep foundations are available, or the new loads are no more than half the calculated previous loads on the existing deep foundations. The engineer shall determine and certify that the existing deep foundations are sound and meet the requirements of this code.

1810.2.8 Special types of deep foundations.

The use of types of deep foundations not specifically mentioned herein is permitted, subject to the approval of the commissioner, upon the submission of acceptable test data, calculations and other information relating to the structural properties and load capacity of such deep foundations. The allowable stresses shall not in any case exceed the limitations specified herein.

1810.2.9 Minimum spacing of deep foundations.

Minimum spacing of deep foundations shall: (i) provide for adequate distribution of the load on the deep foundation group into the supporting soil or rock, (ii) account for installation effects, and (iii) be in accordance with the recommendations of Section 1810.2.2.

1810.2.10 Deep foundations located near a lot line.

Deep foundations located near a lot line shall be designed on the assumption that the adjacent lot will be excavated to a depth of 10 feet (3048 mm) below the nearest legally established curb level. Where such excavation would reduce the embedded length of the deep foundation, the portion of the deep foundation exposed shall be deemed to provide no lateral or vertical support, and the load-carrying determination shall discount the resistance offered by the soil that is subject to potential excavation.

1810.2.11 Splices.

Splices shall be constructed so as to provide and maintain true alignment and position of the component parts of the deep foundation element during installation and thereafter and shall be of adequate strength to transmit the vertical and lateral loads (including tensions) and the moments occurring in the deep foundation section at the location of the splice without exceeding the allowable stresses for such materials as established in Table 1810.8. In all cases, splices shall develop at least 50 percent of the bending capacity of the deep foundation. In all cases, splices situated in the upper 10 feet (3048 mm) of the deep foundation shall be capable of resisting (at allowable working stresses) the applied moments and shears. For individual deep foundation elements or groups comprised of two deep foundation elements, splices in the upper 10 feet (3048 mm) also shall be capable of resisting the moment and shear that would result from an assumed eccentricity of the load on the deep foundation of 3 inches (76.2 mm). For deep foundations located near a lot line, the applied moment and shears of such deep foundations shall be determined on the basis that the adjacent site will be excavated to a depth of 10 feet (3048 mm) below the nearest established curb level as required in Section 1810.2.10.

Exception: For caissons core beams, the splice shall develop the lesser of 50 percent of the capacity of the core in bending or twice the design bending moment carried by the core at the location of the splice, provided that the core splice is not within two caisson diameters of any splice in the casing.

1810.2.12 Protective treatment of deep foundation materials.

Where boring records or site conditions indicate possible deleterious action on deep foundation elements because of soil constituents or other aggressive environmental factors (such as chemical seepage, the presence of salt water, electrical current, changing water levels or other factors), the deep foundation elements shall be adequately protected by materials, methods or processes approved by the engineer. Protective materials shall be applied to the deep foundations so as not to be rendered ineffective by driving. The effectiveness of such protective measures for the particular purpose shall have been thoroughly established by satisfactory service records or other evidence.

Deep foundations installed in ash, garbage, or cinder fills; deep foundations that are free-standing in or near a seawater environment; deep foundations used for the support of chemical plants or coal storage; deep foundations under similar conditions of chemical seepage or aggressive action; and deep foundations that are used for support of electrical generating plants, shall be investigated regarding the need for special protective treatment. Where special protective treatment is indicated by the engineer, such deep foundations shall be protected against deterioration by encasement, coating or other device acceptable to the engineer.

1810.2.13 Minimum concrete cover.

The minimum concrete cover for cast-in-place and precast concrete piles shall be as shown in Table 1810.2.13.

Table 1810.2.13 Minimum Concrete Cover for Cast in Place and Precast Concrete Piles

a

Foundation Element or Condition

Minimum Cover 

1. Precast nonprestressed deep foundation elements

Exposed to seawater

3 inches

Not manufactured under plant conditions

2 inches

Manufactured under plant control conditions

In accordance with Section 20.6.1.3.3 of ACI 318

2. Precast prestressed deep foundation elements

Exposed to seawater

2.5 inches

Other

In accordance with Section 20.6.1.3.3 of ACI 318

3. Cast-in-place deep foundation elements not enclosed by a steel pipe, tube or permanent casing

2.5 inches

4. Cast-in-place deep foundation elements enclosed by a steel pipe, tube or permanent casing

1 inch

5. Structural steel core within a steel pipe, tube or permanent casing

2 inches

6. Cast-in-place drilled shafts enclosed by a stable rock socket

1.5 inches

For SI: 1 inch = 25.4 mm.

a. The concrete cover provided for prestressed and nonprestressed reinforcement in foundations shall be no less than the largest applicable value specified in Table 1810.2.13. Longitudinal bars spaced less than 1 1/2 inches (38.1 mm) clear distance apart shall be considered bundled bars for which the concrete cover provided shall also be no less than that required by Section 20.6.1.3.4 of ACI 318. Concrete cover shall be measured from the concrete surface to the outermost surface of the steel to which the cover requirement applies. Where concrete is placed in a temporary or permanent casing or a mandrel, the inside face of the casing or mandrel shall be considered the concrete surface.

1810.3 Allowable deep foundation loads.

Allowable deep foundation loads shall be determined in accordance with Sections 1810.3.1 through 1810.3.5.

1810.3.1 Determination of allowable individual axial compressive loads.

The allowable individual axial compressive loads on deep foundations shall be the lesser of the allowable structural capacity of the element or the allowable geotechnical capacity of the element. This allowable load shall be determined by an engineer experienced in geotechnical engineering and shall be approved by the commissioner as described below:

1. The allowable structural capacity of the deep foundation shall be determined in accordance with Sections 1810 through 1816.

2. The allowable geotechnical capacity of the deep foundation shall be calculated using a recognized method of analysis and a minimum factor of safety of 2 with respect to failure.

3. The allowable geotechnical capacity shall be demonstrated by load tests.

Exceptions:

1. Allowable loads for deep foundations installed by jacking shall be determined in accordance with Section 1810.3.2.

2. Caisson piles socketed into Class 1a through 1c material as defined in Table 1806.1.

3. Driven deep foundations with allowable loads less than or equal to 40 tons (392.7 kN) (30 tons (294.2 kN) for timber piles).

4. Micropiles with allowable loads less than or equal to 20 tons (196.1 kN), provided all of the following criteria are satisfied:

4.1. The maximum allowable bond stress between the soil and the grout is less than or equal to 4 psi (27.6 kPa).

4.2. The minimum bond zone diameter is greater than or equal to 9 inches (228.6 mm).

4.3. The bond zone is formed entirely in Class 3b or better soils.

1810.3.1.1 Group effects.

The allowable load determined in Section 1810.3.1 shall account for group effects on deep foundations. The analysis of group effects shall be performed by an engineer experienced in geotechnical engineering and calculated using recognized methods of analysis. This analysis shall include a bearing capacity and settlement analysis of the anticipated group(s) of deep foundations and shall consider the presence of weaker soil strata that may be present below the deep foundation element.

1810.3.1.2 Down-drag.

Where deep foundations are installed through subsiding fills or other subsiding strata and derive support from underlying firmer materials, consideration shall be given to the downward frictional forces that may be imposed on the deep foundations by the subsiding upper strata.

1810.3.1.3 Bearing stratum.

The plans for the proposed work shall establish, in accordance with the requirements relating to allowable bearing pressure, the bearing stratum to which the deep foundations in the various sections of the building must penetrate and the approximate elevations of the top of such bearing stratum. Where penetration of a given distance into the bearing strata is required for adequate distribution of the loads, such penetration shall be shown on the plans. The indicated elevations of the top of the bearing strata shall be modified by such additional data as may be obtained during construction. All deep foundations shall penetrate to or into the designated bearing stratum.

1810.3.2 Deep foundations installed by jacking or other static forces.

The allowable capacity of a deep foundation installed by jacking or other static forces shall be not more than 50 percent of the load or force used to install the deep foundation to the required penetration, except for deep foundations jacked into position for underpinning. The allowable capacity of each deep foundation used for permanent underpinning shall not exceed the larger of the following values: 2/3 of the total jacking force used to obtain the required penetration if the load is held constant for 7 hours without measurable settlement; or 1/2 of the total jacking force at final penetration if the load is held for a period of 1 hour without measurable settlement. The jacking resistance used to determine the working load shall not include the resistance offered by nonbearing soils, soils which are to be excavated or soils where support will dissipate with time.

1810.3.3 Helical piles.

The allowable axial compressive load for helical piles shall be in accordance with the requirements of Section 1814.

1810.3.4 Allowable uplift load.

Where required by the design, the allowable uplift load for a single deep foundation shall be determined in accordance with accepted engineering practices based on a minimum factor of safety of three or by uplift load tests performed in accordance with Section 1810.4.2.1. Where uplift load tests are performed, the maximum allowable uplift load shall not exceed the ultimate load capacity divided by a factor of safety of two. The allowable uplift load for a deep foundation group shall not exceed the sum of the allowable uplift loads of the individual deep foundations in the group, nor the uplift capacity calculating the group action of the deep foundation in accordance with accepted engineering practice where the calculated ultimate group capacity is divided by a safety factor of 2.5.

1810.3.5 Allowable lateral load.

The allowable lateral load of a single deep foundation element or a group thereof shall be determined by an approved method of analysis in accordance with accepted engineering practice. The maximum allowable lateral load of a deep foundation shall be 1 ton (8.9 kN), unless verified by lateral load test. Load testing, where required, shall be in accordance with Section 1810.4.3. See Sections 1810.4.3.1 and 1810.4.3.2 for determining the allowable lateral load from the results of lateral load tests.

1810.3.5.1 Group effects.

Lateral capacities for deep foundation groups shall be modified to account for group effects in accordance with accepted engineering practice.

1810.4 Load tests.

Where required, deep foundations shall be load tested in accordance with the requirements of Sections 1810.4.1 through 1810.4.3.

1810.4.1 Compressive load tests.

Where load tests are required per Section 1810.3 or 1810.4.1.1.1, the deep foundations shall be load tested in accordance with the applicable section.

1810.4.1.1 Required number of load tests.

Where load tests are required, at least one test shall be performed in each area of the foundation site within which the subsurface soil conditions are "substantially similar" in character, as determined by the engineer, and at least one test shall be performed for each deep foundation type for the entire foundation installation of the building or group of buildings on a site occupying a total area of 5,000 square feet (464.5 m

2

) or less. Where load tests are required, at least two load tests shall be performed for a site having a footprint between 5,000 square feet (464.5 m

2

) and 30,000 square feet (2787.1 m

2

), and one additional load test shall be performed for each 20,000 square feet (1868.1 m

2

) of added footprint area. For conditions where multiple deep foundation types or capacities are used, refer to Section 1810.2.5.

1810.4.1.1.1 Additional load tests.

Where load bearing capacities of the installed deep foundations are in doubt, are considered non-conforming by the engineer, or where required by the commissioner, additional deep foundation elements shall be load tested to establish the allowable capacity. For friction-based deep foundations where the actual production deep foundation lengths vary more than 25 percent from that of the deep foundations initially installed and load tested, the engineer shall determine if additional load tests are required to establish the allowable capacity of the deep foundation. The number of additional load tests shall be determined by the engineer or commissioner.

1810.4.1.2 Load test apparatus and inspection requirements.

The apparatus and structure to be used in making the load test shall be designed by an engineer. Load tests shall be performed under the observation of the special inspector. A complete record of such tests shall be filed with the commissioner.

1810.4.1.3 Compressive load test procedures.

Compressive load tests shall be conducted in accordance with ASTM D1143 standard procedures and the following conditions:

1. Dial extensometer gages shall provide readings to the nearest 0.001 inch (0.025 mm). Electrical transducers may be used to make settlement observations, provided that backup measurements are made utilizing dial extensometers as described herein at sufficient times to validate the transducer readings.

2. If the allowable axial compressive load is less than or equal to the Basic Maximum Allowable Loads on Deep Foundations in Table 1810.4.1.3, the total test load shall remain in place for a minimum of 12 hours, and shall be held until the average rate of settlement as measured over a 12-hour period does not exceed 0.001 inches (0.025 mm) per hour. The total load shall be removed in decrements not exceeding 25 percent of the total load at 1 hour intervals or longer. For cases where the allowable load on the deep foundation is greater than the values prescribed in Table 1810.4.1.3, refer to Section 1810.4.1.5.

3. In addition to observations required by ASTM D 1143, settlement observations shall be performed 24 hours after the entire test load has been removed.

Exception: A static load test for drilled deep foundations using an embedding load transfer mechanism shall be considered acceptable, provided that the test is performed in general accordance with ASTM D 1143 – Quick Load Test Method. The deep foundation shall be suitably instrumented to evaluate the load transfer through soil or rock at multiple locations along the shaft.

4. Any temporary supporting capacity that the soil might provide to the deep foundation during a load test, but which would be dissipated with time, shall be eliminated by casing off or by other suitable means, such as increasing the total test load to account for such temporary capacity.

Table 1810.4.1.3 Basic Maximum Allowable Pile Loads

Type of Pile

Maximum Allowable Pile Load (tons)

Caisson Piles

No upper limit

Open-end pipe (or tube) piles bearing on rock of Class 1a, 1b, or 1c

18-in O.D. and greater 250 14-in to 18-in O.D. 200 12-in to 14-in 150 10-in to 12-in 100 8-in to 10-in 60

Closed-end pipe (or tube) piles, H-piles, cast-in-place concrete, enlarged base piles, and precast concrete piles bearing on rock of Class 1a, 1b, or 1c

150

Piles (other than timber or helical piles) bearing on soft rock of Class 1d

80

Piles (other than timber or helical piles) that receive their principal support other than by direct bearing on rock of Class 1a through 1d

75

Timber piles bearing on rock of Class 1a through 1d

25

Timber piles bearing in suitable soils

40 tons maximum permissible with load test, 30 tons maximum without load test

Helical piles

30 tons maximum permissible

For SI: 1 ton = 907.18 kg.

1810.4.1.4 High strain, dynamic compressive test methods.

High strain, dynamic compressive test methods performed in accordance with ASTM D 4945 shall be permitted to be used where two or more load tests are required and subject to the approval of the commissioner. In such case, at least one high strain dynamic test shall be performed as a calibration on a static load tested deep foundation or nearby deep foundation driven to comparable resistance. No more than one-half of the required number of load tests may be performed by high strain dynamic methods. High strain dynamic tests shall be performed under the supervision of an engineer experienced in the methods used. The number of high strain dynamic tests shall be at least twice the number of replaced static load tests.

1810.4.1.5 Acceptance criteria.

The allowable load of a deep foundation shall be the lesser of the two values computed as follows:

1. Fifty percent of the applied load causing a net settlement of the tested deep foundation of not more than 1/100 of 1 inch per ton (0.25 mm per 8.9 kN) of applied load. Net settlement in this paragraph is defined as gross settlement due to the total test load minus the rebound after removing 100 percent of the test load.

2. Fifty percent of the applied load causing a net settlement of the tested deep foundation of 3/4 inch (19.1 mm). Net settlement in this paragraph is defined as the gross settlement due to the total test load less the amount of elastic shortening in the deep foundation section due to total test load. The elastic shortening shall be calculated as if the deep foundation is designed for end-bearing or friction. Alternatively, the net settlement may be measured directly using a telltale or other suitable instrumentation.

1810.4.1.5.1 Substantiation of higher allowable loads.

The basic maximum allowable loads of deep foundations tabulated in Table 1810.4.1.3 may be exceeded where a higher value can be substantiated on the basis of load tests and analysis, except for the loads for timber and helical piles. The provisions of Section 1810.4.1 shall be supplemented, as follows: the final load increment shall remain in place for a total of not less than 24 hours; single tested deep foundations shall be subjected to cyclical loading in accordance with ASTM D 1143 or suitably instrumented with telltales and strain gauges so that the movements of the tip and butt of the deep foundation may be independently determined and load transfer to the soil evaluated. A complete record demonstrating satisfactory performance of the test shall be submitted to the commissioner.

1810.4.2 Uplift load test.

Where uplift load tests are required, one uplift load test shall be conducted in each area of substantially similar subsurface conditions up to 5,000 square feet (465 m

2

) of building footprint where deep foundations are subjected to uplift, and not less than two uplift load tests shall be conducted for each area of building footprint where deep foundations are subjected to uplift between 5,000 square feet (465 m

2

) and 30,000 square feet (2787.1 m

2

) and for such area one additional uplift load test shall be conducted for each 20,000 square feet (1858.1 m

2

) of additional area of building footprint where deep foundations are subject to uplift. For conditions where multiple types or capacities of deep foundations are used, refer to Section 1810.2.5.

1810.4.2.1 Uplift load test procedures.

Uplift load tests shall be conducted in accordance with ASTM D 3689 standard procedures and the following conditions:

1. Dial extensometer gages shall provide readings to the nearest 0.001 inch (0.025 mm). Electrical transducers may be used to make settlement observations provided that backup measurements are made utilizing dial extensometers as described therein at sufficient times to validate the transducer readings.

2. Any temporary supporting capacity that the soil might provide to the deep foundation during a load test, but which would be dissipated with time, shall be eliminated by casing off or by other suitable means, such as increasing the total test load to account for such temporary capacity.

1810.4.2.2 Uplift load test apparatus and inspection requirements.

The apparatus and structure to be used in making the load test shall be designed by an engineer. Load tests shall be performed under the observation of the special inspector. A complete record of such tests shall be filed with the commissioner.

1810.4.3 Lateral load tests.

Where testing is required, lateral load tests shall be performed in accordance with ASTM D 3966. A minimum of two deep foundations shall be tested for every area of similar subsurface conditions. For conditions where multiple types or capacities of deep foundations are used, refer to Section 1810.2.5.

1810.4.3.1 Free headed deep foundations.

For deep foundations whose heads are to be designed to be free to rotate in the final structure, the maximum test load shall be at least twice the proposed design working load. In the absence of specific project requirements as determined by the engineer, the resulting allowable load shall not be more than one-half of that test load that produces a gross lateral movement of 1 inch (25.4 mm) of the deep foundation at the ground surface.

1810.4.3.2 Fixed headed deep foundations.

For deep foundations whose heads are designed to be fixed in the final structure, the results of the load test shall be used to verify the input parameters used in the lateral load analysis. In the absence of specific project requirements as determined by the engineer, the allowable load shall be the load that produces a gross lateral movement of 3/8 inch (9.5 mm) of the deep foundation at the ground surface in the lateral load analysis.

1810.4.3.3 Lateral load test procedures.

Lateral load tests shall be conducted in accordance with ASTM D 3966 standard procedures. In addition, dial extensometer gages shall provide readings to the nearest 0.001 inch (0.025 mm). Electrical transducers may be used to make deflection observations, provided that backup measurements are made utilizing dial extensometers as described herein at sufficient times to validate the transducer readings.

1810.4.3.4 Load test apparatus and inspection requirements.

The apparatus and structure to be used in making the load test shall be designed by an engineer. Lateral load tests shall be performed under the observation of the special inspector. A complete record of such tests shall be filed with the commissioner.

1810.5 Installation.

Installation of deep foundations shall be subject to the requirements of Sections 1810.5.1 through 1810.5.8.

1810.5.1 Protection of deep foundations during installation.

Deep foundations shall be handled and installed to the required penetration and resistance by methods that leave the deep foundations' strength unimpaired and that develop and retain the deep foundations' required load-bearing resistance. Any damaged deep foundation shall be satisfactorily repaired or the deep foundation shall be rejected. As an alternative and subject to the approval by the commissioner, deep foundations that are damaged, misaligned, or do not reach their design tip elevation may be used at a reduced fraction of the design load based on an analysis by the engineer.

1810.5.2 Equipment.

Equipment and methods of installation shall be such that deep foundations are installed in their proper position and alignment without damage. Equipment shall be maintained in good working order.

1810.5.3 Preexcavation.

The use of jetting, augering or other methods of preexcavation shall be subject to the approval of the commissioner. Where permitted, preexcavation shall be carried out in the same manner as used for deep foundation elements subject to load tests and in such a manner that will not impair the carrying capacity of the deep foundation elements already in place or damage adjacent structures. The element tips of deep foundations shall be advanced below the preexcavated depth until the required resistance or penetration is obtained.

1810.5.4 Minimum penetration of deep foundations.

Deep foundations shall penetrate the minimum distance required to develop the required load capacity of the deep foundation as established by the required penetration resistance and load tests as applicable.

1810.5.5 Damage to adjacent structures or deep foundations.

Deep foundations shall be installed in such a manner and sequence as to prevent distortion or damage that affects the structural integrity of the deep foundations being installed, or previously installed adjacent deep foundations. The sequence of the installation shall avoid compacting the surrounding soil to the extent that other deep foundations cannot be installed properly, and shall prevent ground movements that are capable of damaging adjacent structures. Deep foundations shall be installed with adequate provision for the protection of adjacent buildings and property.

1810.5.6 Identification.

All deep foundation elements shipped or delivered to the job site shall be identified for conformity to the specified grade and this identification shall be maintained continuously from the point of manufacture to the point of installation. Such shipment or delivery shall be accompanied by a certification from the material supplier or manufacturer indicating conformance with the construction documents. Such certification shall be made available to the engineer of record and the department. In the absence of adequate data, deep foundation elements shall be tested by an approved agency to determine conformity to the specified grade. The approved agency shall furnish a certification of compliance to the engineer of record, or upon request to the commissioner.

1810.5.7 Deep foundation location plan.

A plan showing the location and designation of deep foundations by an identification system shall be filed with the commissioner prior to installation of such deep foundations. Detailed records for individual deep foundations shall bear an identification corresponding to that shown on the plan.

1810.5.8 Installation of deep foundations.

Deep foundations within the area of influence of a given, satisfactorily tested deep foundation shall be installed to the same installation criteria as the satisfactorily tested deep foundation. The same equipment that was used to install the satisfactorily tested deep foundation, identically operated in all aspects, shall be used to install the deep foundation. All deep foundation shall be of the same type, size and shape as the satisfactorily tested deep foundation. All deep foundations within the area of influence as represented by a given satisfactorily tested deep foundation shall bear in, or on, the same bearing stratum as the satisfactorily tested deep foundation.

1810.6 Tolerances.

Tolerances for deep foundations shall be in accordance with the requirements of Sections 1810.6.1 through 1810.6.4.

1810.6.1 Tolerance in the location of the head of the deep foundation.

A tolerance of 3 inches (76.2 mm) from the designed location shall be permitted in the installation of each deep foundation as measured from its head, without reduction in load capacity of the deep foundation group unless otherwise noted on the foundation plans. When deep foundations are installed outside of this tolerance, the true loading on such deep foundations shall be analytically determined from a survey that defines the actual location of the deep foundations as installed and using the actual eccentricity in the deep foundation group with respect to the line of action of the applied load.

1810.6.2 Out of plumb tolerance.

If the axis of any deep foundation is installed out of plumb or deviates from the specified batter by more than 4 percent, the design of the foundation shall be modified to resist the resulting vertical and lateral forces. In types of deep foundations for which subsurface inspection is not possible, this determination shall be made on the exposed section of the deep foundation, which at the time of checking axial alignment, shall not be less than 2 feet (609.6 mm) in length. In deep foundations that can be checked for axial alignment below the ground surface, the sweep of the deep foundation axis shall not exceed 4 percent of the embedded length.

1810.6.3 Deep foundations that are bent during installation.

The load-bearing capacity of deep foundations discovered to have a sharp or sweeping bend shall be determined using an approved method of analysis by the engineer responsible for the deep foundation design in accordance with accepted engineering practice or by load testing a representative deep foundation.

1810.6.4 Deep foundations that are mislocated during installation.

The maximum compressive load on any deep foundation due to mislocation shall not exceed 110 percent of the allowable design load. If the total load on any deep foundation, so determined, is in excess of 110 percent of the allowable load-bearing capacity, correction shall be made by installing additional deep foundations or by other methods of load distribution as required to reduce the maximum load to 110 percent of the allowable deep foundation capacity.

1810.7 Lateral support.

Lateral support for deep foundation elements shall be in accordance with the requirements of Sections 1810.7.1 through 1810.7.4.

1810.7.1 Buckling of deep foundations.

Any soil other than soil with no shear strength shall be deemed to afford sufficient lateral support to the deep foundation to prevent buckling and to permit the design of the deep foundation in accordance with accepted engineering practice and the applicable provisions of this code.

1810.7.2 Unbraced deep foundations.

Deep foundation elements standing unbraced in air, water or soils with no shear strength shall be designed as columns in accordance with the provisions of this code. Such deep foundations driven into firm ground can be considered fixed and laterally supported at 5 feet (1524 mm) below the ground surface and in soft material at 10 feet (3048 mm) below the ground surface unless otherwise prescribed by the engineer.

1810.7.3 Bracing at tops of deep foundations.

Deep foundations shall be braced to provide lateral stability and resist eccentric loads and moments in all directions. Three or more deep foundations connected by a rigid cap shall be considered braced, provided that the deep foundations are located in radial directions from the centroid of the group not less than 60 degrees (1 rad) apart. A group of two deep foundation elements in a rigid cap shall be considered to be braced along the axis connecting the two deep foundations. Methods used to brace deep foundations shall be subject to the approval of the commissioner.

Deep foundations supporting walls shall be driven alternately in lines spaced at least 1 foot (304.8 mm) apart and located symmetrically under the center of gravity of the wall load carried, unless effective measures are taken to provide for eccentricity and moments due to lateral forces, or the deep foundations supporting the wall are adequately braced. A single row of deep foundations without bracing is permitted for one and two-family dwellings and lightweight construction not exceeding two stories or 35 feet (10 668 mm) in height, provided the centers of the deep foundations are located within the width of the wall.

1810.7.4 Bracing of short deep foundations.

All pile caps supported by deep foundations that penetrate less than 10 feet (3048 mm) below cutoff level or less than 10 feet (3048 mm) below ground level shall be braced against lateral movement. Such bracing may consist of connection to other pile caps that encompass deep foundations embedded more than 10 feet (3048 mm) below those levels. The heads of the deep foundations shall be fixed in the cap. In no case shall more than fifty percent of the deep foundations in the foundation of any building penetrate less than 10 feet (3048 mm) below cut-off level or less than 10 feet (3048 mm) below ground level.

Exception: The requirements of this section shall not apply to caisson piles.

1810.7.4.1 Deep foundations located near a lot line.

Where the embedded length of deep foundations located near a lot line would be reduced to less than 10 feet (3048 mm) by excavation of the adjacent site to a depth of 10 feet (3048 mm) below the nearest established curb level, the provisions of Section 1810.7.4 shall apply.

1810.8 Allowable stresses.

Allowable stresses for deep foundations shall be as listed in Table 1810.8.

Exception: Allowable stresses greater than those specified in Table 1810.8 in Sections 1811 and 1812 shall be permitted where supporting data justifying such higher stresses are filed and approved by the commissioner.

Table 1810.8 Allowable Axial Stresses for Materials Used in Deep Foundation Elements

a

Material Type and Condition 

Maximum Allowable Stress

b

1. Concrete or grout in compression

c

Cast-in-place with a permanent casing in accordance with Section 1812.5.2

0.4 f'

c

Cast-in-place in a pipe, tube, other permanent casing or rock

0.33 f'

c

Cast-in-place without a permanent casing

0.3 f'

c

Precast nonprestressed

0.33 f'

c

Precast prestressed

0.33 f'

c

- 0.27 f

pc

2. Nonprestressed reinforcement in compression

0.4 f

y

 £ 30,000 psi

3. Structural steel in compression

Cores within concrete-filled pipes or tubes

0.5 F

y

 £ 32,000 psi

Pipes, tubes or H-piles, where justified in accordance with Section 1810.4.1.5.1

0.5 F

y

 £ 32,000 psi

Pipes or tubes for micropiles or caissons less than 14 inches in diameter

0.4 F

y

 £ 32,000 psi

Other pipes, tubes or H-piles

0.35 F

y

 £ 16,000 psi

Helical piles

0.6F

y

 £ 0.5F

u

4. Nonprestressed reinforcement in tension

Within micropiles or caissons less than 14 inches in diameter

0.6 f

y

Other conditions

0.5 f

y

 £ 24,000 psi

5. Steel in tension

Structural steel cores in caisson piles,

0.5 F

y

 £ 32,000 psi

Pipes, tubes or H-piles, where justified in accordance with Section 1810.4.1.5.1

0.5 F

y

 £ 32,000 psi

Other pipes, tubes or H-piles

0.35 F

y

 £ 16,000 psi

Helical piles

0.6 F

y

 £ 0.5 F

u

6. Timber

See Section 1811.5.4

For SI: 1 pound per square inch = 6.895 kPa.

a. For combined stresses, the structural capacity shall be computed in accordance with AISC 360 for steel piles and ACI 318 for concrete piles.

b.

f'

c

is the specified compressive strength of the concrete or grout; f

pc

is the compressive stress on the gross concrete section due to effective prestress forces only; f

y

is the specified yield strength of reinforcement; F

y

is the specified minimum yield stress of steel; F

u

is the specified minimum tensile stress of steel.

c. The stresses specified apply to the gross cross-sectional area for precast concrete piles. The stresses specified shall apply to the concrete cross-sectional area for all other deep foundation elements. Where a temporary or permanent casing is used, the inside face of the casing shall be considered the concrete surface.

1810.9 Seismic design of deep foundations.

Seismic design of deep foundation elements for structures assigned to Seismic Design Categories C & D shall be performed in accordance with Sections 1810.9.1 and 1810.9.2.

1810.9.1 Seismic Design Category C.

Where a structure is assigned to Seismic Design Category C in accordance with Section 1613, individual pile caps or deep foundations shall be interconnected by ties. Ties shall be capable of carrying, in tension and compression, a force equal to the lesser of: (i) the product of the larger of the pile cap or column design gravity load times the seismic coefficient, S

DS

, divided by 10, or (ii) 25 percent of the smaller of the deep foundation or column design gravity load, unless it can be demonstrated that equivalent restraint is provided by reinforced concrete beams within slabs on grade, reinforced concrete slabs on grade, or confinement by competent rock, hard cohesive soils or very dense granular soils.

1810.9.1.1 Connection to pile cap.

For structures assigned to Seismic Design Category C or D in accordance with Section 1613, deep foundation elements consisting of concrete shall be connected to the pile cap by embedding the element reinforcement or field-placed dowels anchored in the element into the pile cap for a distance equal to their development length in accordance with ACI 318. It shall be permitted to connect precast, prestressed deep foundations to the pile cap by developing the element prestressing strands into the pile cap, provided the connection is ductile. For deformed bars, the development length is the full development length for compression, or tension in the case of uplift, without reduction for excess reinforcement in accordance with Section 25.4.10 of ACI 318. Alternative measures for laterally confining concrete and maintaining toughness and ductile-like behavior at the top of the element shall be permitted, provided the design is such that any hinging occurs in the confined region. The minimum transverse steel ratio for confinement shall not be less than one-half of that required for columns.

For resistance to uplift forces, anchorage of steel pipes, tubes or H-piles to the pile cap shall be made by means other than concrete bond to the bare steel section. Concrete-filled steel pipes or tubes shall have reinforcement of not less than 0.01 times the cross sectional area of the concrete fill, developed into the cap and extending into the concrete fill a length equal to two times the required cap embedment, but not less than the development length in tension of the reinforcement.

Exception: Anchorage of concrete-filled steel pipe piles is permitted to be accomplished using deformed bars developed into the concrete portion of the deep foundation. Splices of deep foundation segments shall develop the full strength of the deep foundation, but the splice need not develop the nominal strength of the deep foundation in tension, shear and bending when the splice has been designed to resist axial and shear forces and moments from the load combinations of Section 12.4 of ASCE 7.

1810.9.1.2 Design details.

Moments, shears and lateral deflections used for design of deep foundations shall be established considering the nonlinear interaction of the shaft and soil, as recommended by the engineer. Where the ratio of the depth of embedment of the center-to-center diameter or width of deep foundations is less than or equal to six, the deep foundation may be assumed to be rigid. Group effects from soil on lateral deep foundation nominal strength shall be included where deep foundation center-to-center spacing in the direction of lateral force is less than eight diameters. Group effects on vertical nominal strength of deep foundations shall be included where deep foundation center-to-center spacing is less than three diameters. The uplift soil nominal strength of deep foundations shall be taken as the uplift strength as limited by the frictional force developed between the soil and the deep foundation.

Where a minimum length for reinforcement or the extent of closely spaced confinement reinforcement is specified at the top of the deep foundation, provisions shall be made so that those specified lengths or extents are maintained after deep foundation cutoff.

1810.9.2 Seismic Design Category D.

Where a structure is assigned to Seismic Design Category D in accordance with Section 1613, the requirements for Seismic Design Category C given in Section 1810.9.1 shall be met. Provisions of ACI 318, Section 18.13.4, shall also apply when not in conflict with the provisions of Sections 1810 through 1816. Concrete shall have a specified compressive strength of not less than 3,000 psi (20.68 MPa) at 28 days.

Exceptions:

1. Group R or U occupancies of light-framed construction and two stories or less in height are permitted to use concrete with a specified compressive strength of not less than 2,500 psi (17.2 MPa) at 28 days.

2. Detached one and two-family dwellings of light-frame construction and two stories or less in height are not required to comply with the provisions of ACI 318, Section 18.13.4.

3. Section 18.13.4.4(a) of ACI 318 shall not apply to concrete piles.

1810.9.2.1 Design details for deep foundations and grade beams.

Design details for deep foundations and grade beams shall comply with the following:

1. Deep foundations shall be designed and constructed to withstand maximum imposed curvatures from earthquake ground motions and structure response. Curvatures shall include free-field soil strains modified for soil-pile-structure interaction coupled with deformations of deep foundations induced by lateral resistance of deep foundations to structure seismic forces.

2. Concrete piles on Site Class E or F sites, as determined in Section 1613.3.2 of this code, shall be designed and detailed in accordance with Sections 1813.4.1 and 1813.4.2 of ACI 318 within a distance of 7 diameters of the deep foundation element of the pile cap and the interfaces of soft to medium stiff clay or liquefiable strata. For precast prestressed concrete piles, detailing provisions as given in Sections 1811.6.3.2 and 1811.6.3.2.2 of this code shall apply.

3. Grade beams shall be designed as beams in accordance with ACI 318, Chapter 18. When grade beams have the capacity to resist the forces from the load combinations in Section 1605.4 of this code, they need not conform to ACI 318, Chapter 18.

1810.9.2.2 Connection to pile cap.

For deep foundations required to resist uplift forces or provide rotational restraint, design of anchorage of deep foundations into the pile cap shall be provided considering the combined effect of axial forces due to uplift and bending moments due to fixity to the pile cap. Anchorage into the pile cap shall be capable of developing the following:

1. In the case of uplift, the lesser of the nominal tensile strength of the longitudinal reinforcement in a concrete pile, or the nominal tensile strength of a steel pile, or the deep foundation uplift soil nominal strength factored by 1.3 or the axial tension force resulting from the load combinations of Section 12.4 of ASCE 7.

2. In the case of rotational restraint, the lesser of the axial and shear forces, and moments resulting from the load combinations of Section 12.4 of ASCE 7 or development of the full axial, bending and shear nominal strength of the deep foundation.

1810.9.2.3 Flexural strength.

Where the vertical, lateral-force-resisting elements are columns, the grade beam or pile cap flexural strengths shall exceed the column flexural strength.

1810.9.2.4 Battered deep foundations.

The connection between deep foundations that are battered and grade beams or pile caps shall be designed to resist the nominal strength of the deep foundation acting as a short column. Battered deep foundations and their connections shall be capable of resisting forces and moments from the load combinations of Section 12.4 of ASCE 7.