Rising Foundation Installation and Construction Risk
By Gareth Ellery, Senior Engineer and Business Development Director, Cathie Associates
Within the offshore wind industry, there has been a relentless and necessary drive towards cost reduction and commercialization of offshore wind. This cost reduction has been driven largely by the introduction of competition to the developers and operators of offshore wind farms through power purchase mechanisms such as CFD in the UK.
The practical manifestation of this in the world of foundation installation has been:
- Delay of some ‘at-risk’ pre-FID spends on geophysical and geotechnical survey resulting in a fait accompli for some risk discovered post-FID design
- A reduction of spend on post-FID survey to quantify risk such as geological and geotechnical heterogeneity around WTG positions
- Compressed timescales to obtain post-FID survey meaning detailed design may not be fully optimised
- A focus on structural optimization for weight and fatigue to reduce cost with installation risks and contingency planning ill-considered or offloaded to 3rd parties
- Reduced Pre-FID Data Acquisition
The structure by which offshore wind power agreements are now awarded places spend up to the point of contract award potentially at risk. In a low margin environment, that spend associated with survey is viewed critically and the scope of data acquisition is defined by what is necessary to reach FID. Typically, this entails a sufficient type and quantity of data required for the conceptual design and costing of foundations. Data required to appreciate installation risk is deemed of secondary importance.
Taking a pragmatic view, it is certainly possible to support this approach provided the risk is managed and properly examined post-FID. However, this often isn’t the case and post-FID, attempts are commonly made to farm-out the risk to the supply chain. Given the cost pressured environment, contractors are often unable to properly discharge these risks or may not have sufficient data to do so, leaving the developer open to claims or leading to higher costs due to the ‘risk margin’.
- Survey Scope Pressures
Despite many technical papers proving the value return on good survey data, survey scopes are coming under increasing cost pressure. The current practice of at least 1 geotechnical test per location may not give a thorough understanding of heterogeneity and behaviour over a full foundation footprint and potential jack-up emplacement and even abandonment of this approach of geotechnical data acquisition is being considered.
Whilst in the future engineering geophysics may offer the opportunity to reliably measure parameters such as strength or stiffness, this is not currently proven and until it is, geotechnical investigation at each WTG location remains the best means of deriving reliable foundation design. The current role for engineering geophysics is a complement to geotechnical data to explore spatial heterogeneity. This is particularly useful for foundations such as GBS and suction caissons which are more sensitive to heterogeneity than piled methods. In current practice, good spatial geotechnical understanding is paramount and should be gained with geotechnical survey supported by high quality geophysical survey.
- Foundation Design
Soils and rocks are not homogenous; layers can exhibit significant lateral and vertical strength variability, the presence of cobbles and boulders can vary widely and preferentially cemented or indurated layers in soils and rocks deviate markedly from the characteristic geotechnical behaviour of a soil or rock. If these features are not considered in design, issues such as premature refusal or buckling / damage can occur during the installation of piles and suction caissons.
Current trends in industry and projects where Cathie Associates have been engaged have shown that weight optimization is being prioritized ahead of installability. This, in turn, is causing construction delays and costly contract claims. Delays in construction are critical as they increase the time from FID to export of first power and so must be avoided at all costs.
- Construction Risk Management
Aside from geotechnical data at each WTG location, our recent experience in industry is that the potential jack-up footprint is under-appreciated. The latest generation of jack-up vessels may emplace their legs over 100m away from the nearest geotechnical data. Usain Bolt might cover this in less than 10 seconds but over such a short distance it is possible to encounter variations in, for example, soft clay thickness of over 800%. This level of heterogeneity has a profound impact on jack-up operations resulting in restricted work and significant delays. In extreme cases, it may not be possible to safely operate jack-ups within their operational limits resulting in unplanned and more expensive/weather sensitive floating operations.
Cathie Associates’ View
The focus on the acquisition of data for optimization of major CAPEX items is a pragmatic approach in the face of a relatively new cost focused environment. The position taken on risk post-FID, however, is resulting in delays and costly contract claims.
Installation and construction risk cannot be simply divested post-FID in the hope that it will be properly managed and mitigated. Appropriate allowances must be made by the developer and/or contractor post-FID for any additional data collection to properly mitigate and manage risk. Given the demanding timeframes for construction, this needs to be considered pre-FID even if investments are not actually made at this stage.
There are a number of investments in data acquisition, over and above the minimum required, which are appropriate ‘at-risk’:
- UHRS seismic – with sufficient coverage out to around 150m radius from the WTG centre to disclose heterogeneity within the foundation footprint and likely jack-up positions. Enables the developer to determine if the position is installable or if micrositing is required
- Appropriate geotechnical techniques – the use of specialized down-hole techniques and drilling methods can be used to better illuminate installation and construction risk
- Proper integration of geotechnical and geophysical data sets to develop a detailed understanding regarding potential variability
These considerations can result in a reduction in supply chain costs through a reduction in risk pricing and contingencies.
If the construction and installation ‘ground risk’ is to be allocated to the supply chain, due diligence should be performed on the contractors plans to properly determine the nature and severity of the risk and how it will be mitigated.
Post-FID data acquisition should become more commonplace to investigate those remaining risks relating to construction and installation. Such data acquisition campaigns should be able to demonstrate an anticipated ROI before they are commissioned, and the project supply chain should have a proactive input into the scope of such campaigns.
If performed in due time, additional data at this stage can prevent some of the issues which have been witnessed by industry and prevent substantial construction delays.
Note: The opinions, beliefs, and viewpoints expressed in this article do not necessarily reflect the opinions of OffshoreWind.biz.