Monthly Archives: February 2018

I can’t believe they invented it: “factual” vs “interpretative” geotechnical report

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One of the things I’d like the most about my job is the fact that I still learn new things, even on topic were I wrongly believe there is not much more new to see.

This week during a telco with my accomplice in crime Eduardo I’ve discovered a new trick that I suspect has been invented by someone in the US (or possibly in the UK) – the split between “factual” and “interpretative” geotechnical report.

In the countries were I’ve worked until today, the geotechnical survey is usually a huge package of documents full of formulas, picture, diagrams and numbers. I’ve been never touched by the idea that part of the content was somehow different.

However, I’ve discovered that somebody (I bet a lawyer) introduced this categorization.

The Geotechnical Data Report (AKA the “Factual stuff”) would be the part including things like:

  • Pictures
  • Boring logs
  • Trial pits logs
  • Field test (SPT, cone penetration, etc.)
  • Laboratory data (water test, CBR, etc.)

This is the type of things that could safely land in a contract and that should be shared and used by the subcontractor.

However, a civil engineer would like to see other information to do his work. He would expect the type of information that should appear in the Geotechnical Interpretative Report (AKA the “don’t rely on me stuff”), with things like:

  • Ground behaviour of geotechnical units
  • Slope stability
  • Seismicity
  • Geotechnical cross sections
  • Construction methods and proposed technical solutions

Basically, nothing connected with design and construction.

Know you know that, wherever possible, you should ask to the geotechnical survey company for the full package (factual + interpretative) but keep them separate – at least if you face a big project with a high geotechnical risk.

Said that, I also want to reiterate my opinion that a good geotechnical survey can make the difference between a successful project (at least for roads and foundations) and a nightmare project with claims and over cost.

It might be difficult to find the budget for this kind of investigation in the early phases of the project but believe me, it’s worth every euro that you will spend on it.

Financial securities: what's that all about?

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A financial security is an instrument to give a party (for instance, the buyer of a wind turbine foundation) an assurance that the seller (in this case, the company that build the foundation) will perform according to his obligation (that is, will comply with the technical and commercial requirements).

They can have different names – the most usual are “Bonds” and “Guarantees”.

The main difference between the 2 is that a bond is stronger – you can draw upon a bond simply asking the money to the bank, while with a guarantee you need to demonstrate that there is a breach of contract before getting the money.

An additional problem with guarantees is that they are linked to the specific contract in place. Therefore changes to the contract (and changes during construction happen really often) could potentially invalidate the guarantee.

There are quite a few bonds / guarantees that are usually used in a wind farm construction contract.

The most frequents are usually linked to the following  topics

  • Advance Payment: the subcontractor receive money upfront to start the works, but he has to give a bond in exchange.
  • Performance: this bond is draw upon if something goes wrong during the execution of the contract.
  • Warranty: this will cover the obligation of the subcontractor after the execution of the project.

There are other Guarantees frequently seen in the business – one is the Parent Company Guarantee, that  you are going to ask if you are working with a small company that belongs to a greater industrial group with a more solid mother company and the other is the Letter of Credit, that you are normally asking to a bank to confirm that the buyer of your product (for instance, expensive wind turbines) will pay for it.

Bonds, warranties and similar stuff are not free – you have to ask them to your bank and they will cost money, and obviously the bigger the bond the higher the price. Therefore the value of each security, normally expressed as a percentage of the contract, is usually subject of never ending discussions and negotiations between the parties.

Environmental impacts of wind farms

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When I talk about my job with people coming from different businesses I receive often question linked to the “environmental impact” of wind turbines.

This term include various effect related to the construction of a wind farm. They can be summarized in the following categories:

Visual impact

Are wind turbines ugly or not? This is a difficult question. Probably I’m biased, but I think they are beautiful – or at least, better than a nuclear plant, unless you like concrete cooling towers. Some nacelles shape have been designed by artist (like the first Acciona models) or architects, like Enercon’s egg shaped solution. It has been designed by Sir Norman Foster and has been awarded with the Design Council Millennium Products Award, the same prize given to beautiful stuff like the Lotus Elise.

However in several countries a specific study is done to evaluate the visual impact of the turbines. There are several indicator and methodologies, however this is usually done considering the “weighted” average height of the horizon before and after the construction of the wind farms.

Noise generation

New generation turbines use a lot of tricks to keep noise low. Noise is coming above all from the tip of the blade, being the rotating equipment in the nacelle only a secondary source. The “easy” way to limit noise is limit the tip speed of the blade. Other strategies involve special profiles for the blade and software control of the machine to limit noise emission when needed (usually during the night, and/or when the wind is blowing from specific directions).

Electromagnetic interferences

This is easy to measure. In general electricity is generated at a low voltage (around 700 Volt) and MV cables are buried, so this impact is negligible.

Shadow flickering

This is the risk that someone living near the wind farm could experience, for a prolonged length of time, the intermittent shadow of the blades passing in front of the sun. This impact is relatively easy to simulate: there are software that, given the position of the turbines and the meteorological parameters (wind direction, percentage of sunny days) calculate the amount of time an observer located somewhere near the turbine would experience the flickering.

Bird strikes

One of the most discussed issues. You will find quite a lot of studies online, done in countries were wind energy and environmental sensibility is well developed (US, Germany, Spain, etc.). In general my impression is that, compared with other causes of bird death (hunt, high buildings, traffic, etc.), impact with turbine is accountable for a very small percentage.

Additionally modern wind turbines can be equipped with a lot of technology that minimize this risk (bat detectors, LIDAR systems, artificial vision, etc.). I had the pleasure of working at projects were the space between machine was large enough to lower the risk of impact, and additionally the turbines were stopped when migrating birds approaching the wind farms were detected.