How the client saved 400 k€ on foundations?
We´ll start with a real-world case, where we can easily identify the advantages on concentrating attention and proper energy of the design of wind turbine foundations. In a technical due-diligence on an executive design for a Wind Farm located in Europe:
Number of WTG: 12 | Type of WTG: VESTAS 2 MW
Anchoring system: anchor cage | Foundation system: gravity foundation seated on improved soil layer
Water table: 0,00m / GL I – Existing solution presented by the client:
According to the geotechnical report, the chosen technique solution was to apply a soil reinforcement. Which is, comparing to other foundation systems – like pile or simple gravity foundation – the most interesting solution from an economical and technical point of view.
Furthermore, the application of a soil reinforcement with its proper – and necessary – load dissipation layer on the top – allows sometimes to set the seating level closer to the ground level. Considering a water table at natural terrain, this represents an optimal hypothesis while we can reduce the effects of water pressure.
The results given by such dimensioning are based on the soil stresses and are measured according to the limits, standards, and technical specifications. They are shown on the opposite diagram.
II – Optimized solution
However, looking more in detail to the load specifications, it was possible to identify the absence of an important data, which is the specification of the service load case.
This means, the wind turbine manufacturer is supposed to furnish a permanent load case (for example: production of electricity, wind speed, etc.), under which it is not allowed to have a gap between foundation and soil. In other words, the foundation should not lift-off under operational loads.
Indeed, due to the variability of presentation forms existing between the technical specification supplied by the different turbine suppliers, it’s common that some input data like foundation loads, dynamical parameters and/or geometry of the assembly are missing or incomplete in the given document.
So, how can we proceed the verification of this important – and frequently, dimensioning criteria!?
In this particular case it was necessary to identify the service loads information, and it was possible by consulting the turbine supplier’s technical department. After this exchange with the manufacturer, the proper load case has been given and the no-gap condition has been respected under these loading conditions.
III – Saving money
The direct and simple conclusion: experience and a good understanding of the technical specifications and current standards, as well as a good relationship and connections with the manufacturers allows to optimize the foundation design significantly. In this case, the client saved from 400 k€ over its whole wind farm, considering concrete volume, steel weight and earthworks.
Advantages of dealing with the WTG’ foundation designs at the development phase
Managing the budget of a large WF project is quite a complicated task due to its long-term, multidisciplinary, and expensive development phases.
Among the various decisions that the project manager must make, allocating resources at the right time appears to be a very critical and important decision
In our last articles we’ve seen that very often technical designs as geotechnical studies and foundation’s design are moved to the construction phase – when a lot of uncertainties disappeared.
In other words, in order to reduce costs at the development phases, technical designs are set to the nal phases and most often on charge of the contractor.
However, the experience shows that frequently this decision leads to very expensive consequences, impacting signi cantly the enterprise’s budgeting.
These appears very often as incomplete and non-exhaustive geotechnical studies or still as non optimized foundation designs, which can bring extra-costs to the construction phase.
Questions: – What if the soil doesn’t correspond to the studies? – What if the foundation design is undersized? – How to manage with this strategy?
Therefore setting the foundation’s design at the early development phases can bring important advantages, which we can list below:
I. Guarantee of conformity and design quality
The technical designs are submitted only once to the approval by the turbine suppliers, and eventual of cial authorities. In such case the owner is ensured also about the quality and accordance of the studies to the current standards.
II. Time saving: through approval by the turbine suppliers
No need to undertake the technical due- diligence of several designs, saving time and money through this approval phase.
III. Better control over contractor’s BID
All contractors budgeting on the same basis. The price comparison is much easier and allow the developer to focus on the quality of the offered processes instead of understanding and checking quantities and prices.
IV. More accuracy over budgeting and nal implementation costs
Finally, the developer is able to work with more precise values in terms of quantities, costs and time schedule for the construction phase
On the other side, the anticipation of technical designs implies on the acceptance and undertaking with the responsibility over the studies and project assumptions – with consequences on guarantee contracts and insurances.
Project managers and developers are faced here to take the optimal decision, considering also the project size and the available time f rames.
In a qualitative way we advice the anticipation of technical studies to the development phases, generating important costs savings for the whole project.