This paper provides a methodology for optimizing a deepwater mooring layout with respect to ground conditions and gives limitations of the method. Specifically, this paper: 1) describes development of a predictive soil model based on integration of AUV geophysical survey and geotechnical data in an area characterized by complex and discontinuous sand strata interbedded with clays; 2) describes using the predictive model to help optimize a FPSO mooring layout to meet design criteria; 3) presents as-installed results for the suction anchors and demonstrates reliability of the predictive soil model; 4) describes learnings from this project; and 5) discusses limitations of the methodology. Suction-anchor installation was completed successfully and no problems were encountered with respect to soil conditions. The as-installed results thus confirmed the general reliability of the predictive soil model. Sand strata as thin as about 30 cm thick were predicted by the model and their presence was confirmed by increased pump underpressures recorded during anchor installation. The fact that the 5-m-diameter suction anchors “felt” such thin sands was instructive. We demonstrate that, by using appropriate geophysical survey data calibrated with geotechnical information, a model of soil conditions can be developed and used as a tool to predict soil conditions away from geotechnical control points. Confidence in the predictions depends on the amount, type, spatial distribution, and quality of the data available and on the geology of the site. This case history is useful as a model approach for optimizing mooring layout with respect to ground conditions or for other applications where shallow soil conditions are sufficiently complex and variable to affect layout of foundation elements or design. Integrated study of the geophysical/geotechnical data was concurrent with mooring system design in a collaborative effort that directly influenced design iterations. Use of the integrated and iterative approaches described here will help future project teams develop more reliable mooring or other foundation solutions faster and thereby reduce costs.
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