Session: 10-03-01 Anchors and Pipelines I

Paper Number: 80822

80822 - Numerical Investigation of Ship Anchor Penetration in Cohesive Baltic Sea Soil 

One of the main reasons for submarine cable damage is anchor interaction. Sea cables are damaged either by an anchor penetrating the subsoil and coming into direct contact with the cable or by an anchor moving above the cable and inducing a pressure load. A sufficient permanent burial depth is necessary to reduce the risk of submarine cable failure due to anchor penetration into the soil.

This work presents the numerical simulation of the penetration process of three ship anchors (AC-14, Hall, and Spek) in the seabed soil of the Baltic Sea. The simulations are carried out using the Coupled Eulerian-Lagrangian method in Abaqus/Explicit. The geology of the Baltic seabed is variable along the entire region regarding cohesive and noncohesive soils, both at the surface and near the surface. Therefore, two different soil types, typical for the Baltic Sea region (sand and clay), under undrained conditions, will be used. Noncohesive soil is simulated using the hypoplastic constitutive model with the extension of the intergranular strain (Wolffersdorff 1996 and Niemunis 1997). This material model was selected given its accuracy at representing soil's stiffness and shear strength dependence on the pressure level, density, and dilatancy behavior. For the creep, relaxation behavior, and velocity dependence for the cohesive soils, the visco-hypoplastic constitutive model, according to Niemunis (2003), is used. Soil parameters for both constitutive models have been obtained by laboratory tests. The chain and the anchors are modeled as rigid bodies due to the low deformations compared to the soil. The simplified chain links are connected to each other by hinges which allow rotation but no relative displacements between the links. The connection between anchor chain and anchor is implemented in the same manner. Contact stresses in normal direction are modeled based on hard contact and contact stresses in tangential direction are modeled based on Coulomb's law of friction. The anchor chain is pulled through the soil at a constant speed while penetrating it. A parametric study is conducted varying anchor type, mass, speed, and soil type and shows the significant influence of certain parameters on penetration depth.

These results will be used in future work to determine the cable installation depth for each anchor and soil to cover all main interaction cases. Furthermore, future work will focus on the influence of the anchor movement on the submarine cable modeling it as an elastoplastic body with variations in soil layering.

Presenting Author: Duy Anh Dao Institute of Geotechnical Engineering and Construction Management

Authors:

Duy Anh Dao Institute of Geotechnical Engineering and Construction Management
Jürgen Grabe Institute of Geotechnical Engineering and Construction Management