Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
Redundancy of the Foundation System
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| 2.3.5 Redundancy of the Foundation System Like other structural elements, structural redundancy may provide adequate support in case individual elements fail, or the lack of redundancy should be considered in the design of the structure. Pile/shaft groups maybe considered redundant depending on the pile/shaft layout and if there is a sufficient number of piles/shafts in the group. In such a group, if an element (e.g., pile/shaft) fails, other piles/shafts in the group may overcome the deficiency. However, the ability to transfer the load originally resisted by the failing element to the other elements is related to group effects. 30 Deep foundations consisting of a single element are non-redundant. Therefore, when a single drilled shaft is designed to replace a number of driven piles or smaller drilled shafts, the redundancy present in the group of driven piles is lost. Redundancy is typically a more significant consideration for axial capacity than for lateral capacity. Redundancy is typically addressed by resistance factors in the LRFD design platform, which is discussed in Chapter 4. 2.4 EXCLUSIONS There are several types of deep foundations that this document does not address or is not applicable to. Deep foundation elements that have little lateral capacity, such as unreinforced CFAs or vibro concrete columns, are not addressed in this document. Also, speciality foundations or deep foundations that are not common for transportation projects in the US. are not addressed. Examples include helical piles, screw piles, and similar types of foundations. This document is not applicable to continuous cantilevered retaining walls, such as sheetpile walls, secant pile walls, or tangent piles walls, because the methods used for analyzing continuous walls differ from those for analyzing individual or groups of laterally loaded deep foundations. More complex deep foundations systems that use external supports for lateral load resistance, such as anchored piles or braced piles, are also not addressed in this document. |