In the conditions described below, the several parts of the building supported on the different pile types or different pile capacities, 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 1808.4 shall apply separately and distinctly to each different type or capacity of piling or equipment used, or method of installation, except where analysis of the probable, comparative behavior of the different type or capacity of the piling or the method of installation indicates that data on one type or capacity of piling permit a reliable extrapolation of the probable behavior of the piling of other types or capacities. The requirements of this section apply to the following proposed conditions:
- Construction of a foundation for a building utilizing piles of more than one type or capacity;
- Modification of an existing foundation by the addition of piles of a type or capacity other than those of the existing piling;
- 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
- Support of part of a building on piles and part on footings.