Rock installation to optimize positioning of a drilling rig

Scope of Work

In support of a P&A and platform removal scopes, relocate a total volume of 6.961m3 rockdump to support the footprint of a Drilling Rig on two locations. The operation was planned according to design criteria’s from DNV to fulfill stabilisation in the foundation and minimise seabed disturbance.

Due to the environmental constraints of the two locations endeavours had to be made, so far as reasonably practicable, to avoid the use of additional gravel and minimise seabed disturbance wherever possible.

The fundamental of the proposed philosophy was to ‘re-form’ the highest parts of the berms and push the peaks into the adjacent troughs, to reduce overall berm thickness and where necessary remove side wall and outer edges of top pad arrangements (Scalloping), re-depositing the removed rock within the footprint of the proposed berm design.


UK Sector

Main Spread



2,5m3 grab, bucket & 14” suction nozzle

Water Depth



14 days



Image Caption: Picture from onshore testing of new grab

Planning Phase

In the planning phase we went through the scope of work to highlight project specific challenges. Based on the large volume, the conclusion was that a traditional ejector setup was not ideal as main tool on this project. The adaption of known and tested onshore equipment had been transferred to subsea remote operations with great success in the past, and so was the case this time. A 2m3 grab was acquired and tested onshore prior to the offshore execution.

Working with low visibility and hide tide, meant that we had to put in extra initiative to monitor the operation and an echoscope software was brought offshore in addition to the excavator’s existing monitoring system.

  • High tide currents
  • Low visibility
  • Lack of ROV support
  • Precise placement of rock dump
  • Minimize disturbance to surrounding area
  • How to maximize efficiency in execution of SOW
Specific Tooling

The new developed Scanmachine 40Te with the capacity to mount a 2m3 grab

  • High production as well as high precision on placement of material
  • No need for hose handling
  • Less support from ROV needed
  • Works within the given tolerances of +-300mm
  • Commonly used excavation tool onshore

Other Projects

Seabed preparation at Heimdal

Seabed preparation at Heimdal

As preparation towards an upcoming by-pass operation, Scanmudring was contracted to make 4 pits under existing pipelines to create access for client’s PRS (CRU) and Force.

Tunnel excavation in Berlin

Tunnel excavation in Berlin

An S-Bahn expansion project encountered a major problem as too much groundwater penetrated in the area of the tunnel excavation. That is how Scanmudring ended up with our underwater excavator in Berlin!