Historical Development And Assessment Of The Current Api Design Methods For Axially Loaded Pipes

Abstract

The design methods for axially loaded piles contained in the API RP 2A, Recommended Practice for Planning. Designing and Constructing Fixed Offshore Platiorms are continually evaluated and updated. To support this activity, API has fimded research over the past 10-12 years which has resulted in the establishment of an internationally recognized data base of axial pile load tests. Subsequent interpretation of these data led to sigrdllcant changes in the design methods for axially loaded piles for both sand and clay. The sand revisions, first incorporated into the 15th Edition of RP 2A provide improved statistical predictions (bias and coeftlcient of variation) of the sand data base than did the design methods for sand contained in earlier editions. The clay revisitms, first incorporated into the 17th Edition of RP 2A provide a statistical description of the clay data base that is similar to descriptions provided by earlier clay methods. Both the revised clay and sand methods provide a more technically sound framework than the methods contained in earlier editions. The revised methods are contained in the current, i.e., the 20th Edition of RP 2A (1993). These revisions have initiated considerable debate, and have prompted the authors to present their thoughts herein. A discussion of the data base, review of the philosophy and evolution of the design method, and a summary and analysis of the key criticisms are provided. The data have been exceedingly useful in formulating design practice, but in our opinion they are too limited to conclusively resolve many of the important issues. While some moditlcations to the present practice seem to be indicated, the References and figures at end of paper 253 authors believe that when combined with a careful site investigation, attention to installation detail and good engineering judgment, RP 2A continues to provide a sound basis for design of axially loaded piles.

Insights into Plugging of Pipe Piles Based on Pile Dimensions

“…Kraft et al [39] revised the original Lambda method after it was deemed "grossly conservative by industry" [45]. The pile penetration coefficient λ, employed by the original Lambda method for side friction in cohesive soils, was revised to account for the relative pile stiffness by proposing that λ be made a function of the term π 3 [46], which describes soil's compressibility normalized by the pile's compressibility.…”

Field investigation of base resistance of pipe piles in clay

“…25 to a minimum of 0 . 4 for realistically high strength ratios (Pelletier et al, 1993). The normal plug stress is compared with the average ultimate unit end bearing resistance q bu determined from the bearing capacity equation…”