An Insight Into the Influence of Construction Methods on the Lateral Load Capacity of Drilled Deep Foundations

Abstract eng:
Deep foundations are frequently employed in the construction of structures where the loads of the superstructure have to be transferred in an economical way to geotechnical strata that rest beyond the reach of shallow foundations. The operation of drilled deep foundation construction equipment frequently employs pressurized fluids or mechanical rotary actions to agitate and remove the soil. The design of a deep foundation element under lateral loads relies on the “as in place” properties of soil. However, it has been observed that the construction method to drill a foundation frequently changes the properties of the soil as well as the surface interaction of the soil with deep foundation element. This influence changes the lateral support stiffness of the soil on the deep foundation element and the surface contact conditions between the deep foundation element and the soil. Such changes heavily influence the lateral load behavior of the deep foundation due to the lack of lateral soil support or reduced lateral soil stiffness as a result of the construction activity. The construction of a deep-foundation is not an isolated process and there is a difference between the “as-conceived” and the “as-built” foundation. Therefore an estimate has to be made regarding what this influence could be before the design of the deep-foundation is complete. In this paper, two case studies relating to the construction of deep foundations of two high rise buildings in New York City will be presented that highlight the effects stated in the previous paragraphs. An experimental study will also be presented that will be reinforced with an analytical finite element investigation to represent the influence of the construction operations on the lateral load capacities of drilled deep foundations.

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