Limit state design of laterally loaded flexible piles - a critical discussion

摘要

Lirait state design of geotechnical structures includes the analysis of predefined limit states. Conditions describing failure of the ground with catastrophic consequences are usually assigned to the ultimate limit state, whereas design situations in which limit values of e.g. deformations are reached without catastrophic consequences are designated as serviceability limit states. In the case of laterally loaded flexible piles, design is usually based on the well-known Winkler model of a beam resting on an elastic foundation. In this model, loading is transferred to the ground by the subgrade reaction mobilised along the pile depending on the lateral displacements. The design of such piles represents a typical deformation problem. Failure of the ground usually occurs only locally in the upper soil zones, where passive earth pressure is fully mobilised. Global failure involving the whole pile-soil system is unrealistic, as internal failure of the pile would occur first. To cope with the limit state design philosophy, this deformation problem therefore needs to be artificially split up into ultimate and serviceability limit state conditions. On the basis of a fictitious design example, the present paper discusses the difficulties involved with this procedure and the consequences for the design of such piles.