Physical and Numerical Modeling of the Performance of Dynamically Installed Anchors in Clay

Depletion of shallow-water hydrocarbons is increasingly forcing the oil and gas industry to explore in deeper water. Dynamically installed anchors (i.e. torpedo anchors and deep penetrating anchor) are increasingly used as a cost-effective solution for floating offshore structures in deep water environments because their installation cost is largely independent of water depth. In addition, dynamically installed anchors can be deployed accurately, and their performance is less dependent on accurate assessment of the soil shear strength since lower seabed strengths permit greater penetration depths. Despite of the economic advantages afforded by dynamically installed anchors, there remain significant uncertainties in the prediction of the embedment depth and verticality, which is likely to affect their long-term holding capacity. Currently, the holding capacity of the dynamically installed anchors is assessed using conventional pile capacity techniques, which neglect discrepancies in the rate of installation and failure mechanism between them.This paper presents a series of model tests simulating dynamic installation and monotonic pull-out of dynamically installed anchors in normally consolidated clay. The model tests are carried out in a beam centrifuge at 100g, with varying penetration angles, extraction angles and model masses. A special designed apparatus allows model anchors to be penetrated and extracted with different penetration angles. The test results show that for models without fins, no matter by which angle the model penetrated the soil, the smallest value of holding capacity is obtained when the pullout and penetration directions are the same. Results also indicate that the penetration depth linearly increases with the anchor mass. This study also reported the results from finite element (FE) analyses. The Coupled Eulerian-Lagrangian (CEL) approach in the commercial FE package Abaqus/Explicit is carried out to simulate dynamic anchor installation.The findings of this study points to a method of assessing the minimum holding capacity of the anchor and its depth of penetration. Further study is now on-going to study the behavior of finned anchors.Copyright © 2014 by ASME