Statistical Relationships Between Geotechnical Properties of Gulf of Mexico Sediments

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ABSTRACT The design of adequate foundations for offshore installations, of all natures, requires a knowledge of the engineering properties of the sediments from the first dozen meters below the ocean floor. This study presents the profiles of shear strength, water content and bulk (wet) density to a depth of 12 meters for eighty cores retrieved from all provinces of the Gulf of Mexico. Equations of the linear relationships for all data as well as for each physiographic area within the Gulf are presented in order to assist the engineer towards the reliable solution of his problems within the deeper portion of the Gulf of Mexico. INTRODUCTION As part of a continuing program of investigation of the geotechnical properties of marine sediments within the Gulf of México, several hundred cores have been collected from all provinces of the basin over the past seven years. Eighty of these cores were analyzed for shear strength and other mass physical properties throughout their lengths. The object of this paper is to present the results in a statistical form to demonstrate correlations and empirical relationships between certain properties with depth for selected provinces of the Gulf of Mexico. These data may be used as an aid in foundation analyses for the determination of bearing capacities of ocean bottom sediments as required for the rational design of offshore engineering structures to be placed in the deeper portions of the Gulf of Mexico. The data also affords a comparison with similar investigations conducted in other areas, such as those by Holmes and Goodell (1964), Hironaka (1966) and Simpson and Inderbitzen (1971). The latter investigations encompassed relatively small areas and were limited to coring depths of less than two meters. All three employed multiple linear regressions in an attempt to explain the variation of an independent variable (usually shear strength) with respect to other parameters such as depth in core, water content, clay percentage Atterberg limits and carbonate content. In all cases it appears that at least fifty percent of the variability of shear strength can be attributed to either the depth in core or water content and that an increase in the number of variables accounts for only a small additional percentage of the variability. A discussion of the aerial distribution of the data presented herein has been given by Bryant and Delflache (1971) including compression indices for a number of consolidation tests on samples from the Gulf of Mexico. Bryant and Wallin (1968) carried out a rather extensive study on the stability and geotechnical characteristics of marine sediments from the Gulf of Mexico concluding that to a depth of 30 meters below the sediment water interface most sediments in the Gulf are stable in their present environment. An empirical relationship of expected minimum shear strength with depth was also presented. GEOLOGICAL SETTING Ewing and others (1968) have presented a detailed description of the geology and structure of the Gulf of Mexico. Figure 1 is a map of the bathymetry and major physiographic provinces of the Gulf of Mexico which has been further subdivided into major sedimentary areas.