Behavior of Suction Anchor For Horizontal Load From Catenary Line In Cohesionless Soils
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Catenary
Line (geometry)
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As the size of offshore structures has been increasing, the interest for foundation systems with large capacity is also rising. Along with this trend, studies are in progress on suction piles (widely used as mooring anchor systems) which can develop large capacity. In this paper, the concept of multiple suction pile anchors - which are composed of several suction piles connected in parallel - is introduced. Two types of multiple suction pile anchors are presented. In one type, two single-suction piles are connected. The other type is composed of three single-suction piles connected in parallel. The pullout behavior of the single-suction pile anchor and the two types of multiple suction pile anchors are investigated using numerical analysis. Numerical simulations using Abaqus software are performed and the three-dimensional model is deployed to duplicate the body shape of suction pile anchors. The load and displacement of the suction pile anchors are computed under continuous horizontal loading, and the pullout capacity of each type of suction pile anchors is evaluated.
Foundation (evidence)
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Laboratory test data on rigid piles embedded or driven at various angles in cohesionless soils and subjected to oblique pull, 60○ from the horizontal, are presented. The vertical or a slight out-batter pile position gives the greatest resistance, the ultimate loads for a 30○ out-batter being less than 65% of the peak resistance. The pile roughness becomes a significant factor when the relative axial load component reaches a certain limit. A method for analyzing nonlinear load-displacement relationship of a rigid pile is presented.
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Abstract : The following is a summary of literature studies on large cylindrical caissons driven into the seabed by hydrostatic underpressure. These caissons are referred to as Suction piles have been in existence since at least the 1950's. The genesis of suction piles and their study will be covered in a historical review of research on this system This report also includes discussions of other relevant parameters relating to the installation and retention of suction piles. Soil stresses relevant to the installation and use of suction piles will also be examined. Installation procedures, including a discussion of critical suction pressures for installation in clay and sand will also be surveyed. In the area of suction pile retention after emplacement, tensile failure in the soil beneath the pile, reverse end bearing capacity of the system, pile wall friction, pore water pressure, static and cyclic loading conditions, lateral loading of the pile, and tether attachment point will all be considered. These subjects all relate to the installation and performance of suction piles for use in deep sea mooring points for floating structures such as mobile offshore bases.
Mooring
Caisson
Cushion
Seabed
Hydrostatic equilibrium
Hydrostatic pressure
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Closure (psychology)
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Centrifuge
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Embedment
Mooring
Caisson
Seabed
Lateral earth pressure
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Helical anchor consist of some steel shafts with a series of helical steel plates welded on a pitch. During installation, helical anchor was screwed into the ground by using a standard truck or trailer mounted augering equipment. The equipment will apply a rotating moment to the steel shafts to screw the anchors into ground. The torque resistance of the anchor will be monitoring along the installation. When the torque resistance achieved its designed values, it verified that capacity of anchor achieved. Behavior of helical anchor under uplift load in cohesionless soil has been studied using previous researches. Based on a few number of laboratory model results many investigators reported the uplift loading of helical anchor embedded in cohesionless soil, a review of related last works shows that not much research has been done to define the uplift capacity in cohesionless soil, a problem that is often encountered in field. The paper observed that the ultimate uplift capacity is dependent on the relative undrained/drained shear strength of cohesionless soil, the depth ratio of embedment and soil thickness ratio.
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Clay soil
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Suction anchors are used within mooring systems for a range of deep water floating structures. The number of suction anchor systems has increased rapidly over the last two decades due to ease of installation and a well-defined design approach. As with other offshore installations, anchor systems may be subjected to re-assessment during their operational lifetime, due to changes in loading, codes or other issues. Such assessment was performed recently for a floating storage unit (FSU) presently in service in the Norwegian Sea, where the geotechnical design of the anchors was re-evaluated. The re-assessment of this storage unit allowed for a number of changes compared to the original design, including updated loads and load histories as well as changes to the safety factors. The geotechnical aspects of the design were also updated, including more refined analyses and a detailed review of the design soil profiles based on back-analysis of installation data. This paper presents the work done related to the geotechnical holding capacity of the anchors during the assessment project. The work performed highlights the benefit of efficient FE analysis and a thorough evaluation of the soil properties and engineering behaviour.
Mooring
Shear Strength
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Dimensionless quantity
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