A program of research on laterally loaded piles for offshore structure has included field test with an instrument pile, laboratory model testing, and development of correlation for design. The work has been sponsored by a group of five oil companies. Three loading condition are considered to be particularly pertinent to the design of laterally loaded pile in soft normally consolidated marine clay. These are (1) short time static loading, (2) cyclic loading such as would occur during the progressive build-up of the storm, and (3) subsequent reloading with forces less than previously maximums. Good general agreement exist between conventional static-loading ultimate-resistance concept and experimental results, provide due allowances are made for the reduced vertical restraint at shallow depth, where it is insufficient to cofine plastic flow to horizontal planes. Force-deformation characteristic based on approximate theory produce satisfactory agreement between computed and experimental behavior of the pile-soil system. The mechanism of cyclic loading characteristic are qualitatively illustrated by typical results from laboratory model studies. Deterioration in resistance because of cyclic loading is most severe at shallow depth and with large lateral deflection of the pile. A correlation based primarily on result with the instrumented pile tested at Sabine, Texas, gives satisfactory prediction of pile deflection and moment over a wide range of loading condition. Estimates of response for reloading after cycling at a higher load made by considering that most of the lateral soil resistance is estimated for deflection smaller than those previous attained. The correlation are summarized and recommendation given for their use in design. Introduction The ability to make reasonable estimates of the behavior of laterally loaded piles is an important consideration in the design and construction of many offshore installations. This is particularly true in the Gulf of Mexico where large lateral forces are produced by winds and waves associated with hurricane and where the foundation materials in the critical zone near the mudline are often found to be very weak clays. A program of research on laterally loaded piles sponsored by five oil companies is the primary basis for the correlation in this paper. At this time it is intend only that the results be summarized in a form directly in design, but publication of the background research is planned for the near future. Requirement for Analysis and Design There are many different ways in which piles or caissons may be subjected to effect of lateral forces. One such case is show in Fig 1a represent a pile and a leg of a jacket-type structure. The structural analysis problem amounts to that of a complex beam-column on an inelastic foundation. For pile separated by spacing of several diameter or more, the Winkler assumption is useful to facilitate the analysis. This means that the soil is considered as a series of independent layers in providing resistance p to pile deflection y (Fig 1b)

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In an effort to predict ice-structure interaction, a simple mechanism is proposed. The structure is represented by a spring-mass system and the ice is replaced by a succession of elastic-brittle elements which impinge on the structure at a rate determined by the relative motion between the ice and the structure. A computer program is used to solve for the dynamic response of the structure. A number of test cases and variations have been solved, and the results compared with limited laboratory and field measurements that are available. Interesting agreement has been obtained with observed behavior at various ice velocities. It is believed that the present approach can be used to determine reasonably well the response of a structure to an impinging ice sheet. Introduction Since the beginning of the exploitation of the oil reserves in Cook Inlet, significant efforts have been devoted to the study of the loads imposed on offshore structures by ice floes. The most comprehensive of the studies are those of Peyton, who has examined the wide variation of sea ice properties and has conducted both laboratory and field investigations of the interaction of ice with structures (Refs 1 thru 4). His reports include a limited number of field measurements made on drilling structures erected in Cook Inlet where extreme tidal variations and velocities are found. Of primary interest in the present study are the force-time recordings in Ref 1. These records indicate that the measured response of the structure is greatly dependent on the velocity of the ice floe. Fig 1 shows a simplified representation given by Peyton (Ref 3). At relatively high velocities the structure exhibits small-amplitude, high frequency vibrations about a constant mean value. At low velocities the amplitude undergoes severe, low-frequency variations between zero and a maximum level that is approximately double the high-velocity mean. The term "racheting" has been applied to this type of oscillation. It is concluded by Peyton that the structure receives the most severe loading and acceleration when the floe is virtually stopped. Added impetus has been given to the study of ice-structure interaction by a proposed crossing of Turnagain Arm. an extension of Cook Inlet (Ref 5). To gather additional information for design the Alaska Department of Highways has developed preliminary plansfor an instrumented test pier to be erected near the intended location of the crossing. The present analytical study is an outgrowth of considerations related to the design and selection of instrumentation for the facility. The number of analytical studies of ice-structure interaction reported in the literature is quite limited. Typical of these is the work by Kivisild (Ref 6), which appears to be based on elastic plate and membrane theory. These theoretical treatments, however, are not sufficiently general to permit predictions of the forces, velocities, and accelerations necessary for the design and cushioning of the instrumentation for the proposed test structure. In an attempt to improve the understanding of the structural response, a simple mechanical analog has been developed and an associated computer program has been used to study a variety of cases.

Experiments conducted with instrumented model pile segment probes at Harvey and Empire, Louisiana are summarized and the observed behavior interpreted. Correlations are developed for the time rate of strength gain and interim recommendations are given for construction of t-z curves (soil resistance versus axial pile displacement) for use in design. The methods are compared with existing pile test results.

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