Abstract A study of the break-out factor ( Nc ) for plate anchors is presented in this paper. Comparisons among finite element method (FEM) analysis and laboratory results were performed. A soil corresponding to a soft normally consolidated clay was considered. Numerical FEM analyses were performed with the Plaxis® code, using an elasto-plastic model with a Mohr-Coulomb criterion. Undrained soil parameters and an adhesion factor α = 1 were used. Values of Nc factor for axisymmetric and 2D FEM were obtained. Two geometries considering a perpendicular load applied in the anchor area and horizontal anchor position to different depths were studied. In the same way, anchor plates to a reduced scale were tested in a tank containing a soft soil. It was verified that the factors Nc reach constant values beyond a determined depth of the soil. Finally, the experimental and numerical values were compared with suggested methods reported in the literature. 1. Introduction Plate anchors are frequently used as foundation solutions for offshore structures to transmit forces to surrounding soils at various depths. The capacity estimation of the anchor is nevertheless uncertain insofar as there are factors that have a large influence in its behaviour. Examples of such factors include the installation process, soil characteristics, geometry of plates and large numbers of methods used to calculate the holding capacity of the anchors. In this context, this paper presents a study of Nc values, obtained from axisymmetric and plane strain finite element model (FEM) simulations done in Plaxis® code. In addition, it outlines the results of scaled-down plate anchors tested in the laboratory. In both cases, the soil considered was soft clay with deepwater sediment characteristics. The description of specific FEM analyses and laboratory test characteristics taken into account are described. Comparisons with expressions found in literature were made.

ABSTRACT Geotechnical design of various foundation solutions and evaluation of geohazards requires a range of soil parameters, including monotonic and cyclic shear strengths as well as deformation and consolidation characteristics. For deepwater soft clays the determination of these parameters poses special problems, but recent research efforts have led to improved wars of talking these problems. Main emphasis is given to how the undrained shear strength can be determined from laboratory tests on soil samples, but with some references to in situ tests. The problems of sample disturbance are dealt with in some detail including how to quantify the degree of disturbance and how to minimize the disturbance effects by taking special care in the sampling and laboratory testing process and in the interpretation of the test results. Remoulded shear strength is needed in addition to intact shear strength, and it is shown how this parameter depends on equipment and procedures used. It is also shown that strain rate and temperature effects need to be carefully considered, as well as thixotrop and creep. INTRODUCTION Need for soil parameters in deep water field development Information about seabed soil conditions are required for a range of structures that are installed in connection with deepwater field development, including, but not limited to : anchoring of floating structures using one of several possible foundation solutions driven piles suction anchor drag in anchor plate anchor Seabed structures founded directly on the seabed, like templates pipelines, flowlines and risers In addition, soil parameters are required to evaluate a number of potential geohazard problems, and especially stability of sub-marine slopes 1 Overview of soil parameters needed The soil parameters that are needed may be grouped into the following categories: intact and remoulded monotonic shear strengths to evaluate penetration resistance and allowable underpressure for installation of structures like skirt penetration of suction anchors 2,3 monotonic and cyclic shear strengths to evaluate holding or bearing capacity of installed 3,4 , stability of sub-marine slopes 1 and behaviour pipelines and risers. Intact and remoulded shear strengths may be needed. For skirted structures, like suction anchors, both the shear strength of remoulded clay after reconsolidation and the thixotropy of remoulded clay are also required to determine the shear strength along the penetrated skirts with time 5,6 . The effective stresses may be low beneath pipelines and risers, and strengths at low consolidation stress may be important. deformation and consolidation characteristics of intact clay calculate displacements and settlements of structures deformation and consolidation characteristics of remoulded clay and unloading characteristics of intact clay to calculate the stress changes in the remoulded zone along penetrated skirts with time 5,6 and beneath pipelines and risers The structures and the seabed may be subject to various kinds of loading, including submerged structure weight, soil weight, sustained loads from current and wind, impact loads from icebergs and trawler equipment, and cyclic loading from waves, earthquakes or temperature variations.