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Deep foundations shall be designed and detailed in accordance with Sections 1810.3.1 through 1810.3.13.
1810.3.1 Design Conditions
Design of deep foundations shall include the design conditions specified in Sections 1810.3.1.1 through 1810.3.1.6, as applicable.
1810.3.1.1 Design Methods for Concrete Elements
Where concrete deep foundations are laterally supported in accordance with Section 1810.2.1 for the entire height and applied forces cause bending moments not greater than those resulting from accidental eccentricities, structural design of the element using the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605.2 and the allowable stresses specified in this chapter shall be permitted. Otherwise, the structural design of concrete deep foundation elements shall use the strength load combinations specified in ASCE 7, Section 2.3 and approved strength design methods.
1810.3.1.2 Composite Elements
Where a single deep foundation element comprises two or more sections of different materials or different types spliced together, each section of the composite assembly shall satisfy the applicable requirements of this code, and the maximum allowable load in each section shall be limited by the structural capacity of that section.
1810.3.1.3 Mislocation
The foundation or superstructure shall be designed to resist the effects of the mislocation of any deep foundation element by not less than 3 inches (76 mm). To resist the effects of mislocation, compressive overload of deep foundation elements to 110 percent of the allowable design load shall be permitted.
1810.3.1.4 Driven Piles
Driven piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by handling, driving and service loads.
1810.3.1.5 Helical Piles
Helical piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by installation into the ground and service loads.
1810.3.1.6 Casings
Temporary and permanent casings shall be of steel and shall be sufficiently strong to resist collapse and sufficiently watertight to exclude any foreign materials during the placing of concrete. Where a permanent casing is considered reinforcing steel, the steel shall be protected under the conditions specified in Section 1810.3.2.5. Horizontal joints in the casing shall be spliced in accordance with Section 1810.3.6.
1810.3.2 Materials
The materials used in deep foundation elements shall satisfy the requirements of Sections 1810.3.2.1 through 1810.3.2.8, as applicable.
1810.3.2.1 Concrete
Where concrete is cast in a steel pipe or where an enlarged base is formed by compacting concrete, the maximum size for coarse aggregate shall be 3/4 inch (19.1 mm). Concrete to be compacted shall have a zero slump.
1810.3.2.1.1 Seismic Hooks
For structures assigned to Seismic Design Category C, D, E or F, the ends of hoops, spirals and ties used in concrete deep foundation elements shall be terminated with seismic hooks, as defined in ACI 318, and shall be turned into the confined concrete core.
1810.3.2.1.2 ACI 318 Equation (25.7.3.3)
Where this chapter requires detailing of concrete deep foundation elements in accordance with Section 18.7.5.4 of ACI 318, compliance with Equation (25.7.3.3) of ACI 318 shall not be required.
1810.3.2.2 Prestressing Steel
Prestressing steel shall conform to ASTM A416.
1810.3.2.3 Steel
Structural steel H-piles and structural steel sheet piling shall conform to the material requirements in ASTM A6. Steel pipe piles shall conform to the material requirements in ASTM A252. Fully welded steel piles shall be fabricated from plates that conform to the material requirements in ASTM A36, ASTM A283, ASTM A572, ASTM A588 or ASTM A690.
1810.3.2.4 Timber
Timber deep foundation elements shall be designed as piles or poles in accordance with ANSI/AWC NDS. Round timber elements shall conform to ASTM D25. Sawn timber elements shall conform to DOC PS-20.
1810.3.2.4.1 Preservative Treatment
Timber deep foundation elements used to support permanent structures shall be treated in accordance with this section unless it is established that the tops of the untreated timber elements will be below the lowest ground-water level assumed to exist during the life of the structure. Preservative and minimum final retention shall be in accordance with AWPA U1 (Commodity Specification E, Use Category 4C) for round timber elements and AWPA U1 (Commodity Specification A, Use Category 4B) for sawn timber elements. Preservative-treated timber elements shall be subject to a quality control program administered by an approved agency. Element cutoffs shall be treated in accordance with AWPA M4.
1810.3.2.5 Protection of Materials
Where boring records or site conditions indicate possible deleterious action on the materials used in deep foundation elements because of soil constituents, changing water levels or other factors, the elements shall be adequately protected by materials, methods or processes approved by the building official. Protective materials shall be applied to the elements so as not to be rendered ineffective by installation. The effectiveness of such protective measures for the particular purpose shall have been thoroughly established by satisfactory service records or other evidence.
1810.3.2.6 Allowable Stresses
The allowable stresses for materials used in deep foundation elements shall not exceed those specified in Table 1810.3.2.6.
TABLE 1810.3.2.6
ALLOWABLE STRESSES FOR MATERIALS USED IN DEEP FOUNDATION ELEMENTS
MATERIAL TYPE AND CONDITION MAXIMUM ALLOWABLE STRESSa
1. Concrete or grout in compressionb  
Cast-in-place with a permanent casing in accordance with Section 1810.3.2.7 or Section 1810.3.5.3.4
0.4 f 'c
Cast-in-place in 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 fpc
2. Nonprestressed reinforcement in compression 0.4 fy ≤ 30,000 psi
3. Steel in compression  
Cores within concrete-filled pipes or tubes
0.5 Fy ≤ 32,000 psi
Pipes, tubes or H-piles, where justified in accordance with Section 1810.3.2.8
0.5 Fy ≤ 32,000 psi
Pipes or tubes for micropiles
0.4 Fy ≤ 32,000 psi
Other pipes, tubes or H-piles
0.35 Fy ≤ 24,000 psi
0.6 Fy ≤ 0.5 Fu
4. Nonprestressed reinforcement in tension  
Within micropiles
0.6 fy
Other conditions
 
For load combinations that do not include wind or seismic loads
0.5 fy ≤ 30,000 psi
For load combinations that include wind or seismic loads
0.5 fy ≤ 40,000 psi
5. Steel in tension  
Pipes, tubes or H-piles, where justified in accordance with Section 1810.3.2.8
0.5 Fy ≤ 32,000 psi
Other pipes, tubes or H-piles
0.35 Fy ≤ 24,000 psi
0.6 Fy ≤ 0.5 Fu
6. Timber In accordance with the ANSI/AWC NDS
  1. f 'c is the specified compressive strength of the concrete or grout; fpc is the compressive stress on the gross concrete section due to effective prestress forces only; fy is the specified yield strength of reinforcement; Fy is the specified minimum yield stress of steel; Fu is the specified minimum tensile stress of structural steel.
  2. The stresses specified apply to the gross cross-sectional area of the concrete for precast prestressed piles and to the net cross-sectional area for all other piles. Where a temporary or permanent casing is used, the inside face of the casing shall be considered the outer edge of the concrete cross-section.
1810.3.2.7 Increased Allowable Compressive Stress for Cased Mandrell-Driven Cast-in-Place Elements
The allowable compressive stress in the concrete shall be permitted to be increased as specified in Table 1810.3.2.6 for those portions of permanently cased cast-in-place elements that satisfy all of the following conditions:
  1. The design shall not use the casing to resist any portion of the axial load imposed.
  2. The casing shall have a sealed tip and be mandrel driven.
  3. The thickness of the casing shall be not less than manufacturer's standard gage No.14 (0.068 inch) (1.75 mm).
  4. The casing shall be seamless or provided with seams of strength equal to the basic material and be of a configuration that will provide confinement to the cast-in-place concrete.
  5. The ratio of steel yield strength (Fy) to specified compressive strength (f'c) shall be not less than six.
  6. The nominal diameter of the element shall not be greater than 16 inches (406 mm).
1810.3.2.8 Justification of Higher Allowable Stresses
Use of allowable stresses greater than those specified in Section 1810.3.2.6 shall be permitted where supporting data justifying such higher stresses is filed with the building official. Such substantiating data shall include the following:
  1. A geotechnical investigation in accordance with Section 1803.
  2. Load tests in accordance with Section 1810.3.3.1.2, regardless of the load supported by the element.
The design and installation of the deep foundation elements shall be under the direct supervision of a registered design professional knowledgeable in the field of soil mechanics and deep foundations who shall submit a report to the building official stating that the elements as installed satisfy the design criteria.
1810.3.3 Determination of Allowable Loads
The allowable axial and lateral loads on deep foundation elements shall be determined by an approved formula, load tests or method of analysis.
1810.3.3.1 Allowable Axial Load
The allowable axial load on a deep foundation element shall be determined in accordance with Sections 1810.3.3.1.1 through 1810.3.3.1.9.
Exception: Where approved by the building official, load testing is not required.
1810.3.3.1.1 Driving Criteria
The allowable compressive load on any driven deep foundation element where determined by the application of an approved driving formula shall not exceed 40 tons (356 kN). For allowable loads above 40 tons (356 kN), the wave equation method of analysis shall be used to estimate driveability for both driving stresses and net displacement per blow at the ultimate load. Allowable loads shall be verified by load tests in accordance with Section 1810.3.3.1.2. The formula or wave equation load shall be determined for gravity-drop or power-actuated hammers and the hammer energy used shall be the maximum consistent with the size, strength and weight of the driven elements. The use of a follower is permitted only with the approval of the building official. The introduction of fresh hammer cushion or pile cushion material just prior to final penetration is not permitted.
1810.3.3.1.2 Load Tests
Where design compressive loads are greater than those determined using the allowable stresses specified in Section 1810.3.2.6, where the design load for any deep foundation element is in doubt, or where cast-in-place deep foundation elements have an enlarged base formed either by compacting concrete or by driving a precast base, control test elements shall be tested in accordance with ASTM D1143 or ASTM D4945. One element or more shall be load tested in each area of uniform subsoil conditions. Where required by the building official, additional elements shall be load tested where necessary to establish the safe design capacity. The resulting allowable loads shall not be more than one-half of the ultimate axial load capacity of the test element as assessed by one of the published methods listed in Section 1810.3.3.1.3 with consideration for the test type, duration and subsoil. The ultimate axial load capacity shall be determined by a registered design professional with consideration given to tolerable total and differential settlements at design load in accordance with Section 1810.2.3. In subsequent installation of the balance of deep foundation elements, all elements shall be deemed to have a supporting capacity equal to that of the control element where such elements are of the same type, size and relative length as the test element; are installed using the same or comparable methods and equipment as the test element; are installed in similar subsoil conditions as the test element; and, for driven elements, where the rate of penetration (for example, net displacement per blow) of such elements is equal to or less than that of the test element driven with the same hammer through a comparable driving distance.
1810.3.3.1.3 Load Test Evaluation Methods
It shall be permitted to evaluate load tests of deep foundation elements using any of the following methods:
  1. Davisson Offset Limit.
  2. Brinch-Hansen 90-percent Criterion.
  3. Butler-Hoy Criterion.
  4. Other methods approved by the building official.
1810.3.3.1.4 Allowable Shaft Resistance
The assumed shaft resistance developed by any uncased cast-in-place deep foundation element shall not exceed one-sixth of the bearing value of the soil material at minimum depth as set forth in Table 1806.2, up to 500 psf (24 kPa), unless a greater value is allowed by the building official on the basis of a geotechnical investigation as specified in Section 1803 or a greater value is substantiated by a load test in accordance with Section 1810.3.3.1.2. Shaft resistance and end-bearing resistance shall not be assumed to act simultaneously unless determined by a geotechnical investigation in accordance with Section 1803.
1810.3.3.1.5 Uplift Capacity of a Single Deep Foundation Element
Where required by the design, the uplift capacity of a single deep foundation element shall be determined by an approved method of analysis based on a minimum factor of safety of three or by load tests conducted in accordance with ASTM D3689. The maximum allowable uplift load shall not exceed the ultimate load capacity as determined in Section 1810.3.3.1.2, using the results of load tests conducted in accordance with ASTM D3689, divided by a factor of safety of two.
Exception: Where uplift is due to wind or seismic loading, the minimum factor of safety shall be two where capacity is determined by an analysis and one and one-half where capacity is determined by load tests.
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