The allowable individual axial compressive loads on piles shall be the lesser of the allowable structural capacity of the element and 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:
- The allowable structural capacity of the pile shall be determined in accordance with Sections 1808 through 1813 of this code.
- The allowable geotechnical capacity of the pile shall be calculated using a recognized method of analysis, and a minimum factor of safety of 2 with respect to failure.
- The allowable geotechnical capacity shall be demonstrated by load tests.
- Allowable loads for piles installed by jacking shall be determined in accordance with Section 1808.3.2.
- Caissons socketed into Class 1a through 1c material as defined in Table 1804.1.
- Driven piles with allowable loads less than or equal to 40 tons (30 tons for timber piles).
- Micropiles with allowable loads less than or equal to 20 tons, provided all of the following criteria are satisfied:
The allowable load determined in Section 1808.3.1 shall account for pile group effects. 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 pile groups and shall consider the presence of weaker soil strata that may be present below the element.
Where piles 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 piles by the subsiding upper strata.
The plans for the proposed work shall establish, in accordance with the requirements relating to allowable bearing pressure, the bearing stratum to which the piles 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 piles shall penetrate to or into the designated bearing stratum.
The allowable capacity of a pile installed by jacking or other static forces shall be not more than 50 percent of the load or force used to install the pile to the required penetration, except for piles jacked into position for underpinning. The allowable capacity of each permanent underpinning pile 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.
Where required by the design, the allowable uplift load for a single pile 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 1808.4.2.1. 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 pile group shall not exceed the sum of the allowable uplift loads of the individual piles in the group, nor the uplift capacity calculating the group action of the pile in accordance with accepted engineering practice where the calculated ultimate group capacity is divided by a safety factor of 2.5.
The allowable lateral load of a single pile or a pile group shall be determined by an approved method of analysis in accordance with accepted engineering practice. The maximum allowable lateral load of a pile shall be 1 ton (8.9 kN), unless verified by lateral load test. Load testing, where required, shall be in accordance with Section 1808.4.3. See Sections 1808.4.3.1 and 1808.4.3.2 for determining the allowable lateral load from the results of lateral load tests.
Lateral capacities for pile groups shall be modified to account for group effects in accordance with accepted engineering practice.