N.Y.C. Admin. Code § BC 1811: Section BC 1811: Driven Deep Foundations

1811.1 General.

Driven deep foundations shall be designed and installed in accordance with Sections 1810 and 1811.2 through 1811.7. Driven deep foundation elements shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by handling, driving and service loads.

1811.2 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.

1811.2.1 Driving hammer for deep foundations.

The hammer to be used to drive deep foundations shall deliver a maximum energy consistent with the size, strength and weight of the driven deep foundations. The hammer shall travel freely in the leads. The hammer shall deliver its rated energy, and measurements shall be made of the fall of the ram or other suitable data shall be obtained at intervals necessary to verify the actual energy delivered during the final 20 blows of the hammer.

1811.2.2 Cushion or cap block.

The cushion or cap block shall be a solid block of hardwood with its grains parallel to the axis of the deep foundation and enclosed in a tight-fitting steel housing, or other accepted equivalent assembly. If laminated materials are used, their type and construction shall be such that their strength is equal to or greater than hardwood. Wood chips, pieces of rope, hose, shavings, automobile tires or similar materials shall not be used. Cap block cushions shall be replaced if burned, crushed, or otherwise damaged. Other cushion materials may be used subject to the approval of the engineer. The introduction of fresh hammer cushion or pile-driving cushion material just prior to final penetration is not permitted.

1811.2.3 Followers.

Followers shall not be used unless permitted in writing by the engineer responsible for the driving operation of the deep foundation. The required driving resistance shall account for the losses of driving energy transmitted to the deep foundation because of the follower. The follower shall be a single length section, be provided with a socket or hood carefully fitted to the top of the deep foundation to minimize loss of energy and to prevent damage to the deep foundation, and have sufficient rigidity to prevent "whip" during driving.

1811.3 Driving criteria.

The allowable compressive load on steel and concrete piles, where determined solely by the application of an approved wave equation analyses approved by the engineer, shall not exceed 40 tons (392.3 kN). The allowable compressive loads on timber piles, where determined solely by the wave equation analyses approved by the engineer, shall not exceed 30 tons (294.2 kN). For allowable loads greater than these values, the wave equation method of analysis may be used to establish initial driving criteria, but final driving criteria and the allowable load shall be verified by load tests in accordance with Section 1810.4. Minimum driving resistance and hammer energy may be determined in accordance with Tables 1811.3(a) and 1811.3(b).

Table 1811.3(a) Minimum Driving Resistance and Minimum Hammer Energy for Steel H-Piles, Pipe Piles, Precast and Cast-in-Place Concrete Piles and Composite Piles (other than timber)

Minimum Driving Resistance

a, c, d, e

Pile Capacity (tons)

Hammer Energy

b

(ft. lbs.)

Friction Piles (blows/ft.)

Piles Bearing on Soft Rock (Class 1d) (blows/ft.)

Piles Bearing on Rock (Class 1a,1b, and 1c)

Up to 20

15,000

19

48

5 Blows per 1/4 inch (Minimum hammer energy of 15,000 ft. lbs.)

19,000

15

27

24,000

11

16

30

15,000

30

72

19,000

23

40

24,000

18

26

40

15,000

44

96

19,000

32

53

24,000

24

34

> 40

AS PER SECTION 1811.3

For SI: 1 foot = 304.8 mm, 1 ton = 907.18 kg.

a. Final driving resistance shall be the sum of tabulated values plus resistance exerted by nonbearing materials. The driving resistance of nonbearing materials shall be taken as the resistance experienced by the pile during driving, but which will be dissipated with time and may be approximated as described in Section 1811.3.

b. The hammer energy indicated is the rated energy.

c. Sustained driving resistance. Where piles are to bear in soft rock, the minimum driving resistance shall be maintained for the last 6 inches, unless a higher sustained driving resistance requirement is established by load test. Where piles are to bear in soil Classes 2 through 5, the minimum driving resistance shall be maintained for the last twelve inches unless load testing demonstrates a requirement for higher sustained driving resistance. No pile needs to be driven to a resistance that penetrates in blows per inch (blows per 25.4 mm) more than twice the resistance indicated in this table, nor beyond the point at which there is no measurable net penetration under the hammer blow.

d. The tabulated values assume that the ratio of total weight of pile to weight of striking part of the hammer does not exceed 3.5. If a larger ratio is to be used, or for other conditions for which no values are tabulated, the driving resistance shall be as approved by the commissioner.

e. For intermediate values of pile capacity, minimum requirements for driving resistance may be determined by straight line interpolation.

Table 1811.3(b) Minimum Driving Resistance and Hammer Energy for Timber Piles

Pile Capacity (tons)

Minimum Driving Resistance (blows/in.) to be Added to Driving Resistance Exerted by Nonbearing Materials (Notes 1, 3, 4)

Hammer Energy (ft./lbs.) (Note 2)

Up to 20

Formula in Note 4 shall apply

7,500 - 12,000

Over 20 to 25

9,000 - 12,000

14,000 - 16,000

Over 25 to 30

12,000 - 16,000 (single-acting hammers)

Greater than 30

15,000 - 20,000 (double-acting hammers)

For SI: 1 ton = 907.18 kg, 1 inch = 25.4 mm.

Notes:

1. The driving resistance exerted by nonbearing materials is the resistance experienced by the pile during driving, but which will be dissipated with time and may be approximated as described in Section 1811.3.

2. The hammer energy indicated is the rated energy.

3. Sustained driving resistance. Where piles are to bear in soft rock, the minimum driving resistance shall be maintained for the last 6 inches (152.4 mm), unless a higher sustained driving resistance requirement is established by load test. Where piles are to bear in soil Classes 2 through 5, the minimum driving resistance measured in blows per inch (blows per 25.4 mm) shall be maintained for the last 12 inches unless load testing demonstrates a requirement for higher sustained driving resistance. No pile need be driven to a resistance that penetrates in blows per inch (blows per 25.4 mm) more than twice the resistance indicated in this table nor beyond the point at which there is no measurable net penetration under the hammer blow.

4. The minimum driving resistance shall be determined by the following formula:

P

=

2W

h

H

or

P

=

2E

(S + 0.1)

(S + 0.1)

where:

P

= Allowable pile load in pounds.

W

p

= Weight of pile in pounds.

W

h

= Weight of striking part of hammer in pounds.

H

= Actual height of fall of striking part of hammer in feet.

E

= Rated energy delivered by the hammer per blow in foot/lbs.

S

= Penetration of pile per blow, in inches, after the pile has been driven to a depth where successive blows produce approximately equal net penetration.

The value W

p

shall not exceed three times W

h

.

1811.3.1 Capacity as indicated by resistance to penetration.

Where subsurface investigation and general experience in the area indicate that the soil that must be penetrated by the deep foundation consists of glacial deposits containing boulders, or fills containing rip-rap, excavated detritus, masonry, concrete or other obstructions in sufficient numbers to present a hazard to the installation of the deep foundations, the selection of type of deep foundation and penetration criteria shall be subject to the approval of the commissioner, but in no case shall the minimum penetration resistance be less than that stated in Tables 1811.3(a) and 1811.3(b).

1811.4 Installation of driven deep foundations.

Driven deep foundations shall be installed in accordance with Section 1810.2 and Sections 1811.4.1 through 1811.4.3.

1811.4.1 Driving near fresh concrete.

Deep foundations shall not be driven adjacent to fresh concrete that is less than 3 days old without approval by the engineer.

1811.4.2 Heaved deep foundations.

Deep foundations that have heaved during the driving of adjacent deep foundations shall be redriven as necessary to develop the required capacity and penetration, or the capacity of the deep foundation shall be verified by load tests in accordance with Section 1810.4.

1811.4.3 Use of vibratory drivers.

Vibratory drivers shall only be used to install deep foundation elements where the deep foundation is subsequently seated by an impact hammer to the final driving criteria established in accordance with Section 1811.3.

1811.5 Timber piles.

Timber piles shall be designed in accordance with the AWC NDS.

1811.5.1 Materials.

Round timber piles shall conform to ASTM D 25. Sawn timber piles shall conform to DOC PS-20.

1811.5.2 Preservative treatment.

Timber piles used to support permanent structures shall be treated in accordance with this section unless it is established that the tops of the untreated timber piles will be below the lowest groundwater level assumed to exist during the life of the structure as specified in Section 1810.2.12. Preservative and minimum final retention shall be in accordance with AWPA U1 (Commodity Specification E, Use Category 4C) for round timber piles and AWPA U1 (Commodity Specification A, Use Category 4B) for sawn timber piles. Preservative-treated timber piles shall be subject to a quality control program administered by an approved agency. Cuts to timber piles shall be treated in accordance with AWPA M4.

1811.5.3 Defective timber piles.

Any sudden decrease in driving resistance of a timber pile shall be investigated for possible damage. If the sudden decrease in driving resistance cannot be correlated to load-bearing data, the timber pile shall be removed for inspection or rejected.

1811.5.4 Sizes of timber piles.

Timber piles shall be of adequate size to resist the applied loads without creating stresses in the timber pile material in excess of 1,200 psi (8.27 MPa) for piles of southern pine, Douglas fir, oak, or other wood of comparable strength; or 800 psi (5.52 MPa) for timber piles of cedar, Norway pine, spruce or other wood of comparable strength. Timber piles of 25 tons (222.5 kN) of capacity or more shall have a minimum 8-inch tip (203.2 mm) with uniform taper. Timber piles of less than 25 tons (222.5 kN) of capacity shall have a minimum 6-inch (152.4 mm) tip with uniform taper. All timber piles, regardless of capacity, driven to end bearing on bedrock of Classes 1a to 1d and compact gravels and sands of Class 2a shall have a minimum 8-inch (203.2 mm) tip and a uniform taper. Any species of wood may be used for timber piles that conforms to ASTM D 25 and that will stand the driving stresses.

1811.5.5 Lagged or inverted timber piles.

The use of lagged or inverted timber piles is permitted. Double lagging shall be adequately connected to the basic timber pile material to transfer the full load from the basic timber pile material to the lagging without exceeding values of allowable stress as established in Chapter 23. The connection for single lagging shall be proportioned for half the timber pile load. The diameter of any inverted timber pile at any section shall be adequate to resist the applied load without exceeding the stresses specified in Section 1811.5.4, but in no case shall it be less than 8 inches (203.2 mm).

1811.6 Precast concrete piles.

1811.6.1 General.

The materials, reinforcement and installation of precast concrete piles shall conform to Sections 1811.6.1.1 through 1811.6.1.3.

1811.6.1.1 Minimum dimension.

The minimum horizontal dimension shall be 8 inches (203.2 mm). Corners of square precast concrete piles shall be chamfered.

1811.6.1.2 Reinforcement.

Longitudinal steel shall be arranged in a symmetrical pattern and be laterally tied with steel ties or wire spiral spaced not more than 4 inches (101.6 mm) apart, center to center, for a distance of 2 feet (609.6 mm) from the ends of the precast concrete pile; and not more than 6 inches (152.4 mm) elsewhere except that at the ends of each precast concrete pile, the first five ties or spirals shall be spaced 1 inch (25.4 mm) center to center. The gage of ties and spirals shall be as follows:

1. For precast concrete piles having a least horizontal dimension of 16 inches (406.4 mm) or less, wire shall not be smaller than 0.22 inch (5.6 mm) (No. 5 gage).

2. For precast concrete piles having a least horizontal dimension of more than 16 inches (406.4 mm) and less than 20 inches (508 mm), wire shall not be smaller than 0.238 inch (6 mm) (No. 4 gage).

3. For precast concrete piles having a least horizontal dimension of 20 inches (508 mm) and larger, wire shall not be smaller than 1/4 inch (6.4 mm) round or 0.259 inch (6.6 mm) (No. 3 gage).

1811.6.1.3 Installation.

Precast concrete piles shall be handled and driven so as not to cause injury or overstressing in a manner that affects durability or strength. A precast concrete pile shall not be driven before the concrete has attained a compressive strength of at least 75 percent of the 28-day specified compressive strength (f '

c

), and not less than the strength sufficient to withstand handling and driving forces.

1811.6.2 Precast nonprestressed concrete piles.

Precast nonprestressed concrete piles shall conform to Sections 1811.6.2.1 through 1811.6.2.4.

1811.6.2.1 Materials.

Concrete shall have a 28-day specified compressive strength (f '

c

) of not less than 3,000 psi (20.68 MPa).

1811.6.2.2 Minimum reinforcement.

The minimum amount of longitudinal reinforcement shall be 0.8 percent of the concrete section and consist of at least four bars.

1811.6.2.2.1 Seismic reinforcement in Seismic Design Category C.

Where a structure is assigned to Seismic Design Category C in accordance with Section 1613, longitudinal reinforcement with a minimum steel ratio of 0.01 shall be provided throughout the length of precast concrete piles. Within a distance equivalent to three times the diameter of the deep foundation element of the bottom of the pile cap, the longitudinal reinforcement shall be confined with closed ties or spirals of a minimum 3/8-inch (9.5 mm) diameter. Ties or spirals shall be provided at a maximum spacing of eight times the diameter of the smallest longitudinal bar, not to exceed 6 inches (152.4 mm). Throughout the remainder of the precast nonprestressed concrete pile, the closed ties or spirals shall have a maximum spacing of 16 times the smallest longitudinal-bar diameter, not to exceed 6 inches (152.4 mm).

1811.6.2.2.2 Seismic reinforcement in Seismic Design Category D.

Where a structure is assigned to Seismic Design Category D in accordance with Section 1613, the requirements of Seismic Design Category C shall apply, except that transverse reinforcement shall comply with requirements of Section 1812.1.2.5.

1811.6.2.3 Allowable stresses.

For allowable stresses, see Table 1810.8.

1811.6.2.4 Concrete cover.

For concrete cover requirements, see Table 1810.2.13.

1811.6.3 Precast prestressed concrete piles.

Precast prestressed concrete piles shall conform to the requirements of Sections 1811.6.3.1 through 1811.6.3.4.

1811.6.3.1 Materials.

Prestressing steel shall conform to ASTM A 416. Concrete shall have a 28-day specified compressive strength (f '

c

) of not less than 5,000 psi (34.48 MPa).

1811.6.3.2 Design.

Precast prestressed concrete piles shall be designed to resist stresses induced by handling and driving as well as by loads. The effective prestress shall not be less than 400 psi (2.76 MPa) for precast prestressed concrete piles less than 30 feet (9144 mm) in length, 550 psi (3.79 MPa) for precast prestressed concrete piles between 30 and 50 feet (9144 mm and 15 240 mm) in length and 700 psi (4.83 MPa) for precast prestressed concrete piles greater than 50 feet (15 240 mm) in length. Effective prestress shall be based on an assumed loss of 30,000 psi (207 MPa) in the prestressing steel. The tensile stress in the prestressing steel shall not exceed the values specified in ACI 318.

1811.6.3.2.1 Design in Seismic Design Category C.

Where a structure is assigned to Seismic Design Category C in accordance with Section 1613, precast prestressed concrete piles shall have transverse reinforcement in accordance with this section. The minimum volumetric ratio of spiral reinforcement shall not be less than the amount required by the following formula for the upper 20 feet (6096 mm) of the precast prestressed concrete pile.

(Equation 18-1)

where:

A

g

= Pile cross-sectional area square inches (mm

2

).

f '

c

= Specified compressive strength of concrete, psi (MPa).

f

yh

= Yield strength of spiral reinforcement £ 85,000 psi (586 MPa).

P

= Axial load on pile, pounds (kN), as determined from Equations 16-5 and 16-7.

r

s

= Spiral reinforcement index (vol. spiral/vol. core).

Not less than one-half the volumetric ratio required by Equation 18-1 shall be provided below the upper 20 feet (6096 mm) of the pile.

Exception: The minimum spiral reinforcement index required by Equation 18-1 shall not apply in cases where the design includes full consideration of load combinations specified in ASCE 7, Section 2.3.6 and the applicable overstrength factor, W

0

. In such cases, minimum spiral reinforcement index shall be as specified in Section 1811.6.1.2 of this code.

1811.6.3.2.2 Design in Seismic Design Category D.

Where a structure is assigned to Seismic Design Category D in accordance with Section 1613.3.5, the requirements for Seismic Design Category C in Section 1811.6.3.2.1 shall be met, in addition to the following:

1. Requirements in ACI 318, Chapter 18, do not apply, unless specifically referenced.

2. Where the total length of the deep foundation in the soil is 35 feet (10 668 mm) or less, the lateral transverse reinforcement in the ductile region shall occur through the length of the precast prestressed concrete pile. Where the precast prestressed concrete pile length exceeds 35 feet (10 668 mm), the ductile region of the deep foundation shall be taken as the greater of 35 feet (10 668 mm) or the distance from the underside of the pile cap to the point of zero curvature plus three times the least dimension of the precast prestressed concrete pile.

3. In the ductile region, the center-to-center spacing of the spirals or hoop reinforcement shall not exceed one-fifth of the least dimension of the deep foundation element, six times the diameter of the longitudinal strand or 8 inches (203.2 mm), whichever is smaller.

4. Circular spiral reinforcement shall be spliced by lapping one full turn and bending the end of the spiral to a 90-degree (1.6-rad) hook or by use of a mechanical or welded splice complying with Section 25.5.7 of ACI 318.

5. Where the transverse reinforcement consists of circular spirals, the volumetric ratio of spiral transverse reinforcement in the ductile region shall comply with the following:

(Equation 18-2)

but not exceed:

r

s

= 0.21

(Equation 18-3)

where:

A

g

= Pile cross-sectional area, square inches (mm

2

).

f '

c

= Specified compressive strength of concrete, psi (MPa)

f

yh

= Yield strength of spiral reinforcement £ 85,000 psi (586 MPa).

P

= Axial load on pile, pounds (kN), as determined from Equations 16-5 and 16-7.

r

s

= Volumetric ratio (vol. spiral/ vol. core).

This required amount of spiral reinforcement is permitted to be obtained by providing an inner and outer spiral.

Exception: The minimum spiral reinforcement required by Equation 18-2 shall not apply in cases where the design includes full consideration of load combinations specified in ASCE 7, Section 2.3.6 and the applicable overstrength factor, W

0

. In such cases, minimum spiral reinforcement index shall be as specified in Section 1811.6.1.2.

6. When transverse reinforcement consists of rectangular hoops and cross ties, the total cross-sectional area of lateral transverse reinforcement in the ductile region with spacing, s, and perpendicular to dimension, h

c

, shall conform to:

(Equation 18-4)

but not less than:

(Equation 18-5)

where:

f

yh

= Yield strength of transverse reinforcement £ 70,000 psi (483 MPa).

h

c

= Cross-sectional dimension of pile core measured center to center of hoop reinforcement, inch (mm).

s

= Spacing of transverse reinforcement measured along length of pile, inch (mm).

A

sh

= Cross-sectional area of transverse reinforcement, square inches (mm

2

).

f '

c

= Specified compressive strength of concrete, psi (MPa).

The hoops and cross ties shall be equivalent to deformed bars not less than No. 3 in size. Rectangular hoop ends shall terminate at a corner with seismic hooks.

Outside of the length of the pile requiring transverse confinement reinforcing, the spiral or hoop reinforcing with a volumetric ratio not less than one-half of that required for transverse confinement reinforcing shall be provided.

1811.6.3.3 Allowable stresses.

For allowable stresses, see Table 1810.8.

1811.6.3.4 Concrete cover.

For concrete cover requirements, see Table 1810.2.13.

1811.7 Structural steel piles.

Structural steel piles shall conform to the requirements of Sections 1811.7.1 through 1811.7.6.

1811.7.1 Materials.

Structural steel H-piles and structural steel sheet piling shall conform to the material requirements in ASTM A 6. Steel pipe piles shall conform to the material requirements in ASTM A 252. Welded built-up steel piles shall be fabricated from plates that conform to the material requirements in ASTM A 36, ASTM A 283, ASTM A 572, ASTM A 588 or ASTM A 690.

1811.7.1.1 Structural steel pipe piles to be welded.

Structural steel pipe piles to be fabricated or spliced by welding shall be subject to qualification requirements of AWS D1.1 for unlisted base metals. Structural steel pipe piles to be welded shall have a carbon equivalency (CE) not exceeding 0.45 as defined by AWS D1.1 and a sulfur content not exceeding 0.05%. Carbon equivalency and sulfur content shall be determined by mill certificates or by chemical analysis, for a minimum of two samples per 1,000 linear feet (304 800 mm) of pipe or part thereof, where mill certificates are unavailable.

1811.7.1.2 High strength pipe.

High strength pipe meeting the strength requirements of API 5L (N80) and API 5CT (N80) shall be permitted for use as structural steel pipe piles. All such pipe and casing shall meet the minimum tensile requirements of ASTM A 252, Grade 3 with a minimum elongation of 15 percent, except that the yield strength shall be a minimum of 80 ksi (551.6 MPa). The following requirements shall also apply:

1. Mill certificates shall be provided.

2. Where mill certificates are not available, a minimum of two coupon tests per 1,000 linear feet (304 800 mm) of pipe or part thereof shall be performed. Testing procedures shall meet the requirements set forth in Section 18 of ASTM A 252.

3. Welding shall be in accordance with Section 1811.7.1.1. In addition, welded seams and splices shall be complete joint penetration welds. Reinforcing steel shall not be welded to high strength pipe.

1811.7.2 Allowable stresses.

For the allowable stresses for materials used in structural steel piles see Table 1810.8.

1811.7.3 Dimensions of structural steel H-piles.

Sections of structural steel H-piles shall comply with the requirements for HP shapes in ASTM A 6 or the following:

1. The flange projections shall not exceed 14 times the minimum thickness of metal in either the flange or the web and the flange widths shall not be less than 80 percent of the depth of the section.

2. The nominal depth in the direction of the web shall not be less than 8 inches (203.2 mm).

3. Flanges and web shall have a minimum nominal thickness of 3/8 inch (9.5 mm).

1811.7.4 Dimensions of structural steel pipe piles.

Structural steel pipe piles driven open ended shall have a nominal outside diameter of not less than 8 inches (203.2 mm). The pipe shall have a minimum of 0.34 square inches (219.4 mm

2

) of steel in cross section to resist each 1,000 foot-pounds (1356 N´m) of energy from the hammer used to install deep foundation elements or the equivalent strength for steels having a yield strength greater than 35,000 psi (241.3 MPa), or the wave equation analysis shall be permitted to be used to assess compression stresses induced by driving to evaluate if the structural steel pipe pile section is appropriate for the selected hammer. Where pipe wall thickness less than 0.188 inch (4.8 mm) is driven open ended, a suitable cutting shoe shall be provided.

1811.7.5 Built-up structural steel piles fabricated from plates.

Built-up sections of steel piles fabricated from welded plates shall comply with the following:

1. The flange projections shall not exceed 14 times the minimum thickness of metal in either the flange or the web and the flange widths shall not be less than 80 percent of the depth of the section.

2. The nominal depth in the direction of the web shall not be less than 8 inches (203.2 mm).

3. Flanges and web shall have a minimum nominal thickness of 3/8 inch (9.5 mm).

1811.7.6 Structural steel sheet piling.

Individual sections of structural steel sheet piling shall conform to the profile indicated by the manufacturer, and shall conform to the general requirements specified by ASTM A 6.