Subsea foundations

1. A subsea foundation for supporting a pipeline or a pipeline accessory, the foundation comprising:

a mudmat;

at least one pile arranged to anchor the mudmat in use by extending with a relative orientation from the mudmat into seabed soil;

a coupling that couples the pile to the mudmat, the coupling comprising at least one interface member supported by the pile for angular displacement relative to the pile and to the mudmat to accommodate the orientation of the mudmat relative to the pile, the pile supporting the interface member in a direction along a central longitudinal axis of the pile; and

a roll/pitch pivot member between the pile and the interface member, the roll/pitch pivot member being oriented to permit angular movement of the interface member about a transverse axis substantially orthogonal to the central longitudinal axis of the pile.

2. The foundation of claim 1 , wherein the roll/pitch pivot member is located within the pile.

3. The foundation of claim 1 , wherein the interface member extends laterally from the pile.

4. The foundation of claim 3 , wherein the interface member is a beam that extends through the pile and protrudes radially from apertures in the pile.

5. The foundation of claim 1 , wherein the coupling comprises a guide sleeve around the pile, leaving a gap between the pile and the guide sleeve.

6. The foundation of claim 5 , wherein the interface member bridges the gap to be received in a receptacle of the guide sleeve.

7. The foundation of claim 6 , wherein the receptacle provides clearance around the interface member received therein for angular displacement of the interface member relative to the mudmat.

8. A subsea foundation for supporting a pipeline or a pipeline accessory, the foundation comprising:

mudmat;

at least one pile arranged to anchor the mudmat in use by extending with a relative orientation from the mudmat into seabed soil;

a coupling that couples the pile to the mudmat, the coupling comprising at least one interface member supported by the pile for angular displacement relative to the pile and to the mudmat to accommodate the orientation of the mudmat relative to the pile, the pile supporting the interface member in a direction along a central longitudinal axis of the pile; and

a yaw pivot member between the pile and the interface member, the yaw pivot member being oriented to permit angular movement of the interface member about the central longitudinal axis of the pile.

9. The foundation of claim 8 , wherein the yaw pivot member is located within the pile.

10. A method of installing a subsea foundation for supporting a pipeline or a pipeline accessory, the method comprising:

installing a mudmat at a seabed location and subsequently anchoring the mudmat by installing at least one pile that extends with a relative orientation from the mudmat into seabed soil and is coupled to the mudmat;

the method further comprising effecting angular displacement of an interface member relative to the mudmat and to the pile to accommodate the orientation of the mudmat relative to the pile, by effecting angular pitch or roll displacement of the interface member about a transverse axis substantially orthogonal to a central longitudinal axis of the pile while the interface member is supported by the pile in a direction along the central longitudinal axis of the pile.

11. The method of claim 10 , comprising locking the pile to the mudmat.

12. The method of claim 10 , comprising effecting angular yaw displacement of the interface member about the central longitudinal axis of the pile.

13. The method of claim 10 , comprising inserting the pile into a guide sleeve of the mudmat, while leaving a gap between the pile and the guide sleeve.

14. The method of claim 13 , comprising supporting the pile laterally within the guide sleeve using at least one shim in the gap.

15. The method of claim 10 , comprising engaging the interface member with a receptacle as the pile is installed and coupled to the mudmat.

16. The method of claim 15 , wherein the interface member enters the receptacle in a downward direction.