ABSTRACT

The suction anchor develops a vertical breakout resistance by creating a smaller pressure beneath the anchor than the ambient pressure. The breakout behavior of model suction anchors in various soils was described. Based upon the observed failure mechanism together with the Mohr-Coulomb failure theory, a vertical breakout capacity equation for suction anchors was developed. This breakout capacity equation was presented in graphical form to facilitate computations for anchor design. Two numerical examples were given to illustrate engineering applications of the design charts.

The suction anchor could be attached to offshore structures to assist with installation problems and to improve stability during extreme events such as hurricanes. Because of their ability to increase foundation stability, suction anchors could also possibly be used to reduce the mass of needed concrete in gravity structures, and thus reduce the cost of construction. Other potential applications of the suction anchor include the anchorage of research submersibles, bottom coring platforms, and certain salvage and dredging operations. This study provides a method of assessing the value of suction-anchors by predicting anchor capacity from soil properties, anchor geometry, and suction intensity.

INTRODUCTION

The suction anchor utilizes suction to attach to the seafloor and to modify soil conditions thus developing a vertical breakout resistance. Although originally intended to provide short-term anchorage capability, long-term and intermittent uses are possible. The suction anchor is one of many new innovative developments which is likely to find numerous applications in the marine environment.

Potential applications include use as a reaction base for deep sea salvage operations, mining vehicles or bottom penetrometer and coring equipment. Other uses include preconsolidation of soft silts (Valent et al. 1972) to improve sediment properties or seating and removal of bottom supported structures with the advantage of providing temporary support. As applied to gravity-type petroleum structures, the suction anchor could provide additional stability during extreme events such as hurricanes by reducing the material mass necessary for stability and minimizing the potential for liquefaction of granular sediments from cyclic loading. These are but a few of many possible uses of the suction anchor. Undoubtedly, much additional research is necessary before large scale application of the anchor is considered and the feasibility of this advice must first be shown.

The objective of this paper is to summarize progress to date on the vertical breakout behavior of the suction anchor and to illustrate the merits of this anchor. Particular emphasis will be on the design parameters which influence performance of the suction anchor and the theory that has evolved. Design graphs and charts are presented to simplify anchor design, and typical design examples are given to demonstrate use of the graphs and charts.

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