Centrifuge studies of cyclic lateral load-displacement behavior of single piles

Abstract

A meeting was held at the California Institute of Technology, February 26, 1976, between a group representing the American Petroleum Institute (API), and Professors K. L. Lee of UCLA and R. F. Scott of Caltech. Problems relating to the dynamic performance of offshore structures were discussed, in particular with respect to their interaction with foundation soils, and the hazards related to the sliding of those soils on modest slopes. Attention was given to both wave- and earthquake-generated forces, especially on pile-supported structures, with particular consideration directed towards the latter. Although the behavior of structures at a wide variety of locations is of concern, current interest centers on those in the Arctic. The particular point of the discussion regarded current field investigations, laboratory test procedures, determination of soil material properties and behavior under cyclic or dynamic loadings, and analysis including soil-structure interactions. It is felt that improvement is needed in all these areas to improve confidence in the ability of analyses to estimate the performance of offshore structures under design loads. Field data on the performance of full-scale structures under severe loading conditions are urgently required, but are unlikely to be obtained because of the scale of the structures involved and the low probability of having a particular instrumented structure subjected to design loads. Consequently some form of model study seems inevitable to enable alternative design or analysis methods to be checked. A program of implementing this possibility was suggested. It would consist of a program of laboratory tests, and associated analytical efforts, performed at UCLA under the supervision of Professor Lee, to determine the types of test and analysis best suited to the present problem. This program would be addressed by Professor Lee in a complementary proposal. In order to provide the equivalent of field tests which can be employed to check the results of analysis, it was proposed that centrifugal model tests be performed at Caltech under the supervision of Professor Scott, in close cooperation with Professor Lee. These would consist of cyclic tests of simplified, but realistic model structures consisting of one-pile or multi-pile arrangements imbedded in saturated soil. The soil would be the same as is to be used at UCLA in the parallel investigation. The proposal to perform tests on model piles in a centrifuge at Caltech was accepted by the American Petroleum Institute, and work was initiated. Static and cyclic lateral loading tests on model piles in dry and saturated sands and a saturated sandy silt have been performed. This report describes the apparatus, tests, results, and analyses involved in the tests.

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