Our multi-faceted role on SuedLink - the world’s longest underground power cable

All-round vision of sustainability

Capable of carrying 4 GW of clean energy, enough to power 10 million households, the project will accelerate Germany’s journey to carbon neutrality. SuedLink will also connect with the NordLink hydropower subsea line from Norway, supporting wider carbon and climate targets under the EU’s Trans-European Network initiative.

With national and cross-border interests relying on SuedLink’s success, clinical site investigation and planning have been paramount. To meet the project’s high bar of sustainability, preparations have focused on identifying an underground route with minimal impact on the landscape.

Confidence in Fugro’s full service envelope

We were awarded the contract to provide site investigation, geo-environmental and permitting services to support the planning and approval of two lots, A4 (37 km) and B1 (68 km). These are located within the Suedlink route running from east of Bremen to north of Hannover.

Having undertaken similar scopes of work for SuedLink co-developer, TenneT, on previous energy projects in Germany, we were ready to demonstrate the depth of our geotechnical and geoenvironmental capabilities for the planning and impact assessment of this next level in mega-infrastructure.

In addition to processing and integrating huge volumes of site data, we needed to be agile and adapt to changes in technical requirements as the client refined the cable route.

With client trust in our consulting abilities and technical competence, we enjoyed scope to innovate and find efficiencies in our methods and strategies. These would add value across many areas of our input – such as mitigating thermal conductivity from the cable, our ‘gold star’ approach to landowner relations, and the adoption of the GeoDin® geotechnical platform for managing and sharing data for the whole 700 km route.

The platform allowed instant, easy sharing and cross-referencing of data-streams, and also unified the quality and functionality of data viewing and reporting for consultants and subcontractors across the project. This enabled our experts to maintain good communication and continuity with all stakeholders involved in this major project.

Multi-disciplinary team

To meet the wide-reaching scope, we assembled a dedicated, multi-disciplinary team of 60 specialists, from compliance managers and HSSE experts, to soil testing and geotechnical experts. They brought regional experience and continuity to the six-year programme of work, and proven expertise and techniques for the specific challenges of corridor infrastructure like SuedLink.

The introduction of new planning legislation with a tighter framework for environmental permitting required a high degree of flexibility and meticulous organisation. We were able to draw on our regulatory knowledge to ensure we carried out all necessary elements of the process in a timely, efficient and sensitive manner to meet the high bar of environmental approval.

Six key components and their impact on Suedlink project success

1.     Permitting and planning approval support

• Environmental impact assessment (EIA) and environmental planning

• Supporting public consultation and stakeholder management

• Permitting for all field activities

• Technical planning support for routing and alternative options

• Supervision and interpretation of biological and environmental mapping

Highlight: forging effective landowner relations

Permissions work is regulatory and non-negotiable, involving managing right of way (RoW) and documenting procedures and measures to minimise the impacts from site access and activities. But it also requires sensitivity and strong communication with the public and affected stakeholders to bring them onboard.

We supported a thorough and thoughtful approach in building effective relations with local authorities, utility companies, subcontractors, the public and landowners. This included attending public consultation events to provide information and alleviate any potential concerns about the cable route, impact of site work or construction.

With activities requiring access along a significant corridor, there was strong emphasis on creating trust and transparency with landowners, many of them farmers. We made phone calls to the landowners to arrange suitable times for site access and alert them to any changes in plan so that all parties could schedule their daily tasks accordingly. Our ‘gold star’ approach established a culture of cooperation, creating a positive legacy for subsequent stages of the project and prompting positive feedback from the client.

2.     Site supervision

• Client representative for geotechnical investigation activities

• Permitting way of rights support

• Planning coordination and QA/QC of all drilling activities

• Design of investigation programme

• Geotechnical logging

Highlight: HSSE management scores high

Our HSSE responsibilities were significant, with a 100+ km long site to supervise and high safety standards set by the client. We compiled an exhaustive HSSE plan for site investigations and associated access, covering all possible scenarios. This ranged from survey personnel on foot, to major drilling operations by subcontractors extracting thousands of metres of drill cores, with up to six drilling machines operating in parallel. Relying on our vast experience of complex and large projects around the globe, we marked four years on site with no incidents. 

3.     GeoEngineering

• Desk top study

• Geotechnical model

• Geotechnical expert report

• Recommendations for cable route, and river, rail and road crossings

Highlight: Breaking our own record for geological profiling

We created a continuous digital cross section for the 100+ km long corridor combining lots A4 and B1 – setting a new bar for linear profile mapping. In-house software helped us to integrate tens of thousands of borehole metres and CPT data, providing an accurate geotechnical model. This helped the client to make an efficient and coherent evaluation of cable route options, and other decisions on environmental protection and water management. 

4.     Hydrology and hydrogeology

• Desk top studies on hydrology, hydrogeology and dewatering

• Hydrogeological expert report

• Design of groundwater monitoring programme

• Supervision of hydrological testing

• Flood risk assessment

• Water Framework Directive compliance

Highlight: Detailed 3D dewatering model

Dewatering (the removal of groundwater) is a major cost in construction, especially for significant linear infrastructure like SuedLink where a critical power cable is being installed at depth. We integrated complex and varied data to create a highly detailed 3D model to help evaluate and guide effective decisions across all aspects of dewatering. 

The model draws on multiple data streams held in the GeoDin® database, including dewatering tests, surface water and ground water monitoring, water chemistry, and essential parameters from other surveys and remote sensing. Offering flexible ways to extract usable data, it helped planners and designers to:

• determine effective and cost-efficient solutions for pumping water out, ensuring agricultural land, pasture, and wildlife habitat is not adversely affected

• assess the most suitable places for discharging extracted water based on water levels in local water courses levels

• design secure cable crossings over water courses

5.     Soil protection

• Assessment of soil to relevant soil protection code

• Methodology for soil protection measures

• Profiling for thermal conductivity model

• Soil protection mapping and supervision

Highlight: Solving heat issues from HVDC cables

It is vital that heat generated by HVDC cables is conducted away, as this affects their performance and could even necessitate a downgrade in amperage.

Much of the SuedLink northern section, including B1 and A4, is characterised by sedimentary geology. Depending on the level of moisture present, this can lead to varying dry soil conditions that could affect the thermal conductivity of the 525 KV high current cable. As Suedlink will be the longest underground power cable in the world, there were concerns about possible implications to cable efficiency from heat build-up, as well as the impacts from heat transfer on bedding materials and ecology.

To address these issues, we developed a methodology to visualise the thermal conductivity of soil types along the route. We analysed 1150 samples of soil from the 105 km corridor and performed considerable work to model a curve plotting their heat conductivity value against water content, and classify the soils in a novel way. 

Our data helped with the specification of appropriate trench bedding and cable casing to dissipate heat, and hence an important contribution to making future SuedLink operations safe and efficient.

There is no industry or national standard in Germany for the assessment of heat conductivity of soils for HVDC power lines. With heat emission forming part of the environmental assessment, this innovation proved crucial to approvals for SuedLink.

The innovation could offer a much-needed standard approach to soil thermal conductivity for underground HVDC projects around the world.

6.     Laboratory work and sample storage facility

• Sample tracking

• Laboratory index testing

• Geological logging

• Sample storage, including cold storage

Highlight: Fugro’s dedicated soil testing facility

To support the extensive geotechnical work, we created a dedicated laboratory and storage hub to carry out all necessary soil analysis and testing. Conveniently located, our specialists and technicians carried out a full range of testing and core logging, carefully documenting and storing hundreds of samples. This helped us to progress efficiently with all of our geotechnical responsibilities, including our novel work on soil protection and thermal conductivity. We also stored cores from other lots in the storage facility, which included cold storage.

In summary, our work has made positive impacts across many aspects of the project, including:

• Careful site management ensured that months of complex operations did not negatively affect protected species, precious habitat or breeding times for wildlife

• With cone penetration tests (CPT) and environmental investigations being the first operations on site, our high standards of environmental stewardship and excellent stakeholder relations ensured the smooth running of a busy site programme. Cooperation for later project stages

• Our innovative soil heat conductivity work will help mitigate heat transfer that could affect groundwater, watercourses, arable land, wildlife habitat and other aspects of environmental balance

• Our powerful modelling tools helped preserve other important environmental aspects, such as reinstating backfill around the trenching that exactly replicated the original soil layers

• The close location of our soil testing laboratory reduced the impacts of transport and related CO2 emissions