Dredging and mining is shifting to deeper waters. For dredging with TSHD’s the limit is around 150 m of water depth, but for mining the water depth can be hundreds or even thousands of meters. New technologies have to be developed or copied and adapted from the offshore industry.

AN OVERVIEW OF DRAG EMBEDDED ANCHOR HOLDING CAPACITY FOR DREDGING AND OFFSHORE APPLICATIONS.

S.A. Miedema1, G.H.G. Lagers2, J. Kerkvliet3

ABSTRACT

Dredging and mining is shifting to deeper waters. For dredging with TSHD’s the limit is around 150 m of water depth, but for mining the water depth can be hundreds or even thousands of meters. New technologies have to be developed or copied and adapted from the offshore industry. At the Delft University, Offshore Engineering, students carry out research into many subjects related to moorings and mooring systems, like:

1. The holding capacity of drag anchors in sand.

2. The holding capacity of drag anchors in clay.

3. The holding capacity and operations of suction anchors.

4. The use of the catenary equation in moorings.

5. The methodology about choosing the right anchor for different purposes.

6. The methodology about choosing the right anchor line for different purposes and conditions.

7. The methodology about designing an anchoring system for FPSO’s.

8. The methodology about designing an anchoring system for SPAR’s.

9. The methodology about designing an anchoring system for Semi-Sub’s.

The results of the research can also be found on: http://www.offshoreengineering.org. In dredging and offshore
anchors are used for positioning, but also for operations (the cutter suction dredger). In all cases it is evitable that a proper estimation of the holding capacity is very useful when designing the application.

The holding capacity of anchors depends on the digging depth, the soil mechanical properties end of course the dimensions and the shape of the anchor. The digging depth also depends on the soil mechanical properties and the shape of the anchor. Now the first question is of course how is the digging depth related to the soil mechanical
properties and the shape of the anchor and the second question is, how does this relate to the holding capacity.

By means of deriving the equilibrium equations of motion of the anchor and applying the cutting theories, the digging behavior of anchors can be simulated. The main challenges are, how to model the shape of the anchor and how to apply the existing cutting theories to this complex shape. This paper gives a first attempt to derive
equilibrium equations based on the cutting theory of Miedema 1987.

Keywords: Dredging, Anchors, Holding Capacity, Soil Mechanics

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