If you either work for a WTG manufacturer or any electric utility the situation in which you are asked to do a complete analyse of a project very quickly (like in 2 or 3 days) is very common.

You are usually asked to do this task for several reasons:

• Preparation of a first rough layout with preliminary quantities.
• To compare different alternative WTG layouts.
• For a technical due diligences.

Until not so many years this type of assessments was done using the specialized design software: MDT, Civil 3D, Istram-Ispol, Clip, etc.

These programs are more focused on a detailed design and the processes are not easy to adapt to a different scenario, where quick results are required.

In the last years Infraworks has emerged as a powerful alternative.

It is a planning and design platform from Autodesk that has experienced an impressive development. It offers a bunch of very useful tools that can be easily adapted to the BoP design of a wind farm.

Some of the principal qualities are:

• It allows engineers to quickly create a preliminary design in a realistic environment, making possible to position the point of view anywere in the wind fare and immediately be able to visualize the existing conditions.
• The program supports data from multiple sources: GIS (shapefiles, geodatabases, etc), CAD, raster, and all kind of BIM-data. These data is integrated into an interactive 3D model.
• Cloud technology is integrated through BIM 360. Different users from the same team can work dynamically on the same projects in remote - i.e. from any point in the planet, a feature especially useful in these "work from home" days.
• Multiple alternatives called “Proposals” can be generated for the same project.
• The program allows to extract quantities, create shadow analysis, analize conditions with style maps using “style rules”, etc.
• It is that it is very user-friendly: it takes only a few days to learn the basics and start doing your own projects.

One of its major advantages included in the last releases is that it is possible to import detailed designs from other software such as 3Ds Max, Civil 3D or Revit.

What I like the most is the dynamic flow of work implemented in the most recent versions between Infraworks and Civil 3D. In this sense, I like to think about Infraworks as a good complement to Civil 3D. We can either:

• Start the design in Civil 3D and export it to Infraworks.
• Create the predesign directly in Infraworks feeding the model with data available in all kind of source formats: shapefiles, raster, etc.

The synchronization between both programs is not bidirectional: any change done in the Civil 3D model is automatically included in the Infraworks model but not the other way around.

Going more deeply in what the program can offer, here are some comments specific for the wind farm BoP items:

Crane pads

The software offers a quick way to obtain quantities for big construction areas such as crane hardstands.

The option “Land Areas & Grading Behaviours” allows the user to easily calculate quantities for gradings and landfills.

One point to improve is that currently there is no way to export this data to any other format: the information must be extracted "manually" to an external BoQ.

Foundations:

It works in a similar way as explained before with the hardstands.

For example, we can quickly model the foundation bottom pit and calculate the excavation volumes.

We can do it to analyse a certain position or, taking advantage from GIS format files and other formats, do an overall analysis of all the positions.

Roads

Infraworks has two typologies of roads, which will be used depending on the needs of both the designer and the project:

• Planning roads: These are lightweight roads that use spline geometry. You can add planning roads to a model or import roadway data as planning roads. This format does not allow to extract quantities from the model.
• Component roads: these are configurable roads in cross section, vertical and horizontal geometry. They provide a precise control of geometry and grades. This is the type of road we are interested in when creating a BoP design in a wind farm because they have available features such as the grading tool and the mass balance quantification.

The interesting thing about this tool is that we can have a full control of all the parameters from a 3D environment and we can export to quantities to a .csv file format.

Additionally, the intersections between roads are automatically created and very easy to handle and edit.

Drainage

Hydraulics analysis and drainage calculations are hard to deliver in few hours - at least if you want to do a good job.

However, Infraworks offers a useful and easy module to deal with this matter. Some of the main available services are:

• Watershed analysis: it includes point watershed creation, watershed analysis along roads and calculation of flows for a calculated watershed according to different methods (rational, regression, etc).
• Culvert design analysis with automated culvert placement, culvert analysis and culvert reporting
• Roadway inlet and pipe analysis, including automated inlet and pipe placement and inlet and pipe design analysis.

As a drawback, it is worth point out that drainage tools are only available in combination with a BIM 360 account.

Furthermore, depending on the kind of service required, we will need to have "cloud credits" available for certain processes such as culvert analysis.

In any case, it is difficult to find in the market a tool that gives such a powerful and interactive tool for preliminary drainage calculations.

Creation of realistic videos

Useful realistic videos or tours around the model can be created in a very easy way. They could not only look really fancy in a presentation but also are useful to assess whether there is a major mistake in the predesign. You ave an example at the beguinning of this article: the creation of this video took no more than 15 minutes from when the model was ready.

Other options:

There is also the option to create advanced customized cross section profiles.

This could be of great use to model other elements linear elements such medium voltage electrical cable trench or high voltage lines.

Final comments

Beyond all the great functionalities described so far, we must not lose the perspective: as it is now, Infraworks is not intended for a full detailed design. As a user you frequently feel that the program lacks "advanced capabilities" that would be highly appreciated.

Autodesk is aware that the software has a great potential and the company is working constantly to improve the product. To have a good idea of the expected developments in future releases I recommend to visit the webpage “Infraworks Public Roadmap”:

These new developments are based on the feedback given by the users. Suggestions and proposed new features are posted in the “Infraworks Idea Forum”. I have personally posted some of them myself.

I also include the link to the Youtube official channel which I consider a good audio-visual reference for those who want to crack on with the software:

In short, Infraworks is already a tool to take into consideration, not only in preliminary designs but also as a support for final designs.

It will be interesting to see whether future developments will transform in a main reference for designers - not only for wind farm projection, but also for all kind of civil works modelling.

I’ve recently worked on a slope stabilization preliminary project.

Among other action, the use of Vetiver grass for stabilization purposes has been suggested by the customer, who had used it successfully in another wind farm in the same area.

Although this technique is used in Italy and other European country I was not an expert, so I’ve done a search to see the peculiarities of this solution and I want to share the key points I’ve discovered.

Basically, Vetiver is the colloquial name of a plant originating from India and South East Asia.

There are 3 species:

• Chrysopogon zizanioides (formerly known as Vetiveria zizanoides), from southern India: this is the one that you’re going to use – deep roots, sterile and not invasive.
• Chrysopogon nemoralis, from Laos and Vietnam: shorter roots and not sterile.
• Chrysopogon nigritana, from South and West Africa: not sterile.

Vetiver can be used both on cut and fill slopes, up to a 1:1 gradient (45 degrees).

The number of plant that you will need will vary – the horizontal distance between plants should be from 10 to 15 cm, while the distance between rows (measured on the slope) will vary from 1 m. (highly erodible soil) to 2 m. (more stable soil).

First and last rows should be planted at the top and toe of the slope.

As cuts and embankments are not fertile (or at least, they shouldn’t be) fertilizer and watering at regular intervals will be needed. Later on regular cutting will be needed.

It growths very fast (up to 3,5 meters in 12 months).

This solution has several advantages:

• Above all, it’s cheap. This is particularly true in countries where labor wages are low. Also, there are no heavy long term maintenance costs.
• It’s a natural erosion control measure (at least, more natural than a plastic geotextile and less ugly than a rip rap).
• It’s very effective.

There are also some potential problems:

• Intolerance to shading (but this can be an advantage if you use it only as a pioneer plant for initial stabilization).
• Roots don’t penetrate well below water table.
• Need an initial establishment period of 3 to 6 month depending on the climate. During this phase it must be protected from livestock.

You can read more on the subject on this interesting book from the Vetiver System network.

I’ve been recently asked to justify the roadbed thickness for a wind farm I’ve designed.

For several reasons (mainly because the majority of documents are redacted by non-civil engineers) the engineering companies supporting our customer ask for a written demonstration that the road design comply with the requirement of the famous AASTHO 1993 green book.

Unfortunately, it is not possible to use it for wind farms, and I’ll explain you why in this post.

As you will probably know, AASHTO defined an empirical equation  after a series of full scale test done about 50 years ago in the USA, the famous “Road test”.

This equation, very large and complicated indeed, gives as a result the “structural number” (SN) – a number that can be used to define the required roadbed thickness.

The formula looks very complicated, but the idea behind it it’s pretty easy: given the expected number of vehicle using the roads (defined as standard “equivalent single axis loads”) and other physical and project related variables you can define the correct thickness of the various materials selected for the road bed.

This is how the equation looks like:

Where

W18 = Predicted number of 80 kN (18,000 lb.) ESALs (equivalent single axis loads). Basically different type of vehicles (car, trucks, bikes, etc.) will use the road. To simplify the calculation, all this different axes are concerted to “standard axes”.

ZR = Standard normal deviate.

So = Combined standard error of the traffic prediction and performance prediction. Both ZR and So choice depend on the type of the road (for a major highway you will need more confidence in the result, while for a local road you can assume some risk).

SN =Structural Number (an index that is indicative of the total pavement thickness required).

Basically, each layer has a thickness (D) and a “layer coefficient” (a) representing the quality of the material.

In wind farm construction normally only one or two gravel layers are used.

Therefore the equation SN=a1D1 + a2D2m2 + a3D3m3+… will simplify becoming SN=a1D1

a1 = Layer coefficient. Gravel would be around 0.14

D1 = Layer thickness (inches).

ΔPSI = Difference between the initial design serviceability index, p0, and the design terminal serviceability index, pt. This concept is needed to incorporate in the equation the quality of the road at the beginning of the considered timeframe, p0 and the quality of the road at the end of the life span (pt).

MR = sub-grade resilient modulus (in psi). This number indicates the quality of the sub-grade.

Said that, let’s see why this beautiful and highly effective equation is of little (if any) utility for wind farm design.

Basically, a highway or an urban road is damaged by the recurring transit of heavy loads – that is, bus, trucks, etc. This trucks use the road for several years, causing accumulated damage.

What happens in a wind farm is that, when the WTGs are installed and producing, no one will use the internal roads – only a few service cars every now a then. The ESAL number will be almost zero.

What normally damage wind farms internal roads without heavy traffic is poor drainage, incorrect roadbed material selection or poor construction (e.g. incorrect compaction), not cyclical mechanical loads above the elastic limits.

Therefore we normally design the roadbed based on the CBR value: we know that with a very good CBR in dry climates 20 cm are normally enough, while for low to very low CBR (>5) we use 40 to 50 cm.

Below CBR=3% special solutions are normally needed.