Removing the steepest slopes on a surface (ground mounted solar PV application)

[khalidMX3HH]

Hello all, 

I work in the renewable energy sector developing ground mounted solar PV projects.

 

We have 50+ projects on different parcels of land ranging from 2 acres to 28 acres. The racking system we are planning to use can only handle slopes up to 10%. For the first site, I have turned the 3D contours into a surface and run a slope analysis to highlight the areas which are over 10%. I have attached a few images for context.

How can I "smooth" the surface, through a cut and fill process, to make the surface have a maximum slope of 10%? Is there a way for Civil 3D to create a new surface based on the original one, but adhere to a user defined maximum slope?

Any help is greatly appreciated.

 

 

 

[santhoulakis]

In general this is done with the Grading Creation Tools (Home->Create Design->Grading->Grading Creation Tools).

There are various otions there. 

You will need to have a starting feature line and from there you can cut/fill to one of its sides with a slope that you define and select "Grade to Surface", where surface will be your existing one.

The command will find out where the grading work will end based on your slopes and will create a feature line at the other side of grading, which you can add to your proposed surface.

[khalidMX3HH]

Thank you. I tried that and created a rectangle/block to represent the area where the solar array would go. I selected "grading to the outside" as that is what others had in videos online when they were doing building footprints. But should this be "grading to the inside" if the area inside the rectangle is what I want to grade?

 

[Neilw_05]

Does the solution allow for small areas of steep slopes in order to create areas of flat slopes to save a lot of earthwork? So for example, if an area exceeds 10%, can you grade steps at 2:1 or 1:1 to create the flat areas? This could save a lot of earthwork vs. mass grading the entire site at 10% max. You should be able to create a balanced site this way.

[neilyj666]

@khalidMX3HH I'd agree with @Neilw_05 - you will minimise the earthworks and achieve a better solution but you may lose land area due to the additional earthworks batters throughout the site which will reduce the generating capacity of the site which may be an issue.

The Grading Optimization tools may be useful for this project - I haven't used them so couldn't really comment with any authority on this option.

[khalidMX3HH]

No, nowhere in the solar array can exceed 10%. But instead of grading the entire parcel of land, I am breaking the array into smaller areas. The idea being that there will be less earthwork by having multiple smaller areas with a max 10% constraint instead of grading the entire parcel.

When I am using the Grading Creation Tools, should I select "grading to the inside" or "grading to the outside" if I want to grade the area inside the Feature Line?

[khalidMX3HH]

We can't reduce the generating capacity of the site, we are contractually obligated to hit a particular capacity.

Agreed, I will try the Grading Optimization tools as they seem to be most applicable.

[Neilw_05 · Accepted solution]

If I understand your objective is to create areas that exclude the steep slopes, you can create outlines of the areas using polylines, turn them into featurelines, drape them on eg, then use infills to create the TIN. By using infills your surface will have gaps in the steep areas and will not be included in earthwork calcs, contours, etc.

[Neilw_05]

On second thought, you probably want to go the other way and leave the flat areas undisturbed. No sense in regrading if they already meet the slope criteria. In that case there is no need to create a surface at all. Just delineate where the panels can go and lay them out. What am I missing?

[khalidMX3HH]

Thank you Neil. I used the feature line approach, with a rectangle for where the solar array will be. Grading to the outside and infill on the area surface allowed for volume calculation for cut and fill, however this approach (at least how I did it) assumed the entire surface was flat i.e. 0%. That resulted in more cut and fill than expected. 

Ultimately, I decided to install the new Grading Optimization Extension. The Zone tool will allow me to set a minimum drain slope and a maximum slope and the software will optimize the cut and fill. This looks to be the most efficient method for this solar project application.

 

[khalidMX3HH]

Update: I had high hopes for the Grading Optimization tool but could not get it to work. Perhaps my computer is too old but the optimization process never finished after running for an hour. 

I ended up creating a Feature Line out of the array block, setting the corner points to be the same elevation as the existing surface and seeing what the cut and fill would be to keep the array block planar. At the same time I double checked to ensure the new graded surface didn't exceed the 10% slope.