Pull-Out Capacity and Failure Mechanisms of Strip Anchors in Clay

Fernando Cañizal,Jorge Cañizal,César Sagaseta,Jorge Castro

doi:10.3390/en13153853

Abstract

Plate anchors are a well-established solution for supporting the efforts of floating platforms for wind and marine renewable energies. The behavior of ultrathin rigid plate anchors buried in purely cohesive soils under undrained and plane-strain conditions is analyzed. As already known, a dimensional analysis shows that the pull-out capacity of the anchor may be expressed using a weightless break-out factor (Nc0) that only depends on the ratio between the depth and the anchor width (H/B). Using finite element analyses, tabulated values of the weightless break-out factor are provided in this paper and three different failure mechanisms are identified, namely very shallow (quasi-vertical), shallow or intermediate (semi-vertical), and deep (rotational). For very shallow failure mechanisms, the studied problem is completely equivalent to the trapdoor problem because immediate breakaway at the bottom part of the anchor is considered (vented conditions). The existing analytical solutions for the very shallow (Nc0 = 1.956 H/B) and deep cases (Nc = 3π + 2) using the slip-line method are reviewed and an analytical limit is proposed for the first time for the very shallow mechanism (H/B = 1.314). For shallow (intermediate) cases, the failure mechanism is identified and the angle of the main slip lines is numerically evaluated.

Highlights

The increasing demand for renewable energy has resulted in the use of the oceans as an important source of wind and marine renewable energies, posing new challenges for offshore geotechnics.Floating platforms, e.g., floating wind turbines, are the most widely used option in deep and moderate water depths, and anchoring systems are needed to moor these platforms in position and sometimes to provide extra stability
They were traditionally installed by means of dragging, but the development of new keying processes, such as suction-embedded plate anchors (SEPLAs) or dynamically embedded plate anchors (DEPLAs), has led to an increase in their use in the support of offshore floating platforms
SEPLAs and DEPLAs are vertically introduced into the ground with the aid of a suction pile or a torpedo, respectively; they are rotated to thehorizontal position

Summary

Introduction

The increasing demand for renewable energy has resulted in the use of the oceans as an important source of wind and marine renewable energies, posing new challenges for offshore geotechnics.Floating platforms, e.g., floating wind turbines, are the most widely used option in deep and moderate water depths, and anchoring systems are needed to moor these platforms in position and sometimes to provide extra stability. Offshore anchors are foundation elements connected to the floating platform through mooring lines, either catenary or taut types (e.g., [1]). Plate anchors are a well-established solution for the foundation of offshore floating platforms (e.g., [1]) and are essentially steel plates embedded in the seabed, i.e., they are embedded anchors. They were traditionally installed by means of dragging, but the development of new keying processes, such as suction-embedded plate anchors (SEPLAs) or dynamically embedded plate anchors (DEPLAs), has led to an increase in their use in the support of offshore floating platforms.

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