In general, you will have several alternatives to dig your cable trenches:
- Backhoe with hydraulic breaker hammer
The smarter choice will depend on the hardness of the rock.
In general, the use of explosive for trenches in wind farms is extremely rare – it is normally limited to foundation excavation.
Backhoe is always an easy solution, above all in situation where the trenches follow a very irregular path with a lot of change of direction.
However, it’s production is lower when you have compact, very hard rock (for instance, basalts and granites).
On top of that you can have a border of the trench which is not very “clean”, as it could be difficult to open a truly rectangular section.
All in all, it will usually be a better choice in small wind farms on soils or soft,, fractured rock.
The biggest problem with trenchers is that it’s not always easy (or cheap) to find one for your project. They are very performant with long distances, as they can easily open from 1 to 3 meters per minutes in soils (e.g. silts and clays).
Obviously they are somehow slower in rocks. In a very soft one (e.g. gypsum) you should work at a pace of around 1 meter per minute (from 40 to 80 m/h), going all the way down to few meters per hour while you go up in the Mohs scale.
As an order of magnitude, in limestone you would get from 15 to 40 meters per hours, in sandstone from 10 to 30 m/h and in gneiss less than 10 m/h.