Tensar Triax geogrid use in wind farms

Here you have a real world example of geogrid use.

We are in a wind farm in southern Spain, and thanks to previous experience with this technology the client decided to use a Tensar Triax geogrid TX160.

This is a triangular geogrid (the “old school” version was square). It seems that the triangular geometry guarantee a better distribution of the loads

The same geotextile  has been used in many wind farms (more than 100) around the world, with several big project in Germany and UK where in some cases more than half a million square meters have been used. Often the soil was peat (turf), with a very low CBR (even less than 1).

The saving in crushed stone using a geogrid can be around 30% to 40%, so with a price around 2-3 €/sqm it is normally a cost effective solution.

When we opt for this solution we’ve had helpful feedback and hints from Tensar, as they can study the existing info and provide a design based on the soil conditions and the available materials. There are several models available with a different triangular size, so it is not easy to choose the right model.

We haven't had any problem during the first half of the civil works circulating with machinery and trucks, but when we started moving the narrow track crane on the internal roads between the pads significant damages appeared:

Geotextile vs Geogrid: which is the best solution?

This is a debate we are living each time we have to build internal roads on soils with a low (<5) to very low (<2) CBR.

Basically when the others alternatives (mainly soil substitution and soil improvement) are not feasible we are adopting two different solution, either a strong geotextile with reinforcement and separation properties or a geogrid (coupled with a thin geotextile used as a filter if necessary).

Presently both of them are working well, but only after many years we will know which one works best. I'm hearing very different opinion on the subject, so there is not an universal consensus.

As geotextile, both woven and nonwoven alternatives seem reasonable. Both of them provides separation of the aggregate from the subgrade and have high tensile strength and modulus, adding reinforcement to the foundation soil. Right now the woven solution is widely preferred.

As woven geotextile we have used the US250 from US Fabric, with the following properties:

Tensile StrengthASTM D-4632250 lbs1,112 N
Elongation @ BreakASTM D-463215%15%
Mullen BurstASTM D-3786450 psi3,102 kPa
Puncture StrengthASTM D-4833100 lbs445 N
CBR PunctureASTM D-6241900 lbs4,005 N

And as nonwoven, something like the US Fabric US 160NW  looks like the best option:

Weight - TypicalASTM D-52616.0 oz/sy203 g/sm
Tensile StrengthASTM D-4632160 lbs711 N
Elongation @ BreakASTM D-463250%50%
Mullen BurstASTM D-3786305 psi2,103 kPa
Puncture StrengthASTM D-483390 lbs400 N
CBR PunctureASTM D-6241410 lbs1,824 N

Regarding geogrid, it has been used in several wind farms all around Europe. I had a meeting with the representative from Tensar, and their product looks interesting.

It is a triangular net, providing support to the stone aggregate. It works equally well in every direction.

We have used it in Spain, and it have been used in several other projects in UK and Romania.