Adding thickness to a surface

[darrell_kennedy]

Hi all,

As part of the proposed grading for many of my projects the design includes placing a layer of material at a specified thickness on top of either the excavation or existing grade surface. This is an easy thing to do along flat areas, slopes less than approximately 3H:1V, and on constant slope areas; simply copy the base surface into a blank surface definition and raise or lower the elevation of that surface by specified thickness.  However when the grade changes frequently, is not constant, or is steeper than 3H:1V, then the solution of raising or lower the surface by a constant elevation does not work. I essentially want to offset the surface by a specified distance not raise and lower the surface by a specified distance.

To give an example of where this might be used; adding 8" of topsoil to bank slope, adding 18" of stone to existing grade sloped area, etc..

Any ideas?

Thanks.

[Todd_Rogers]

Click on the surface, in the contextual ribbon, select Extract from Surface>Extract Solids from Surface. In the dialog box you have an option to give it thickness.

[ChrisRS]

@Todd_Rogers, I have not experimented with this. Is the thickness measured perpendicularly to the surface or vertically?

The issue with pasting and lowering surfaces is that he distance is always vertical, and does not accurately represent the thickness where teh surface slope is steep.  

[Todd_Rogers]

So, this method will create a solid from the surface, with thickness, that does not interfere with the actual surface. Which is good.

[darrell_kennedy]

I am at that step right now. How can I turn the 3-D solid to a surface though?

[darrell_kennedy]

I exploded the 3d solid twice down to a lines with elevations. I then added these to the surface as objects. It created the surface, however this did not give the offset or thickness I was looking form especially on steep slopes. 

[Todd_Rogers]

I see. I think you might be at a dead end at this point. 😒

[Joe-Bouza]

This is what you want

https://www.autodesk.com/autodesk-university/class/Magic-Dynamic-Differential-TIN-Surface-2012

[Anonymous]

I know what you mean @darrell_kennedy. When offsetting a surface in C3D it always offsets on the vertical plane. If you have a lot of steep slopes it will impact a little on your volumes, (5% for 3H:1V, 10% for 2H:1V and nearly 20% for 1.5H:1V). It also looks rather ugly on the profiles and sections too with the topsoil seeming to thin out a little at steep grades as the depth is shown on the vertical aspect rather than perpendicular to the slope of the surface. I would love a simple solution to this too but I'm not aware of one. As the volumes are only indicative anyway I usually just round up to the nearest big number to account for the extra as it saves the hassle of additional steps.

You may be able to convert a copy of your surface to a mesh and use the AutoCAD 3D surface tools to offset this, which would achieve the desired result, then convert the new offset mesh into a surface (probably by exploding it into 3d faces and then using those to build a new surface). This however would not be dynamic. And it's not something I've done as it just seems like a torturous process that would have to be repeated every time something changes.

On the volumes dashboard you could add bounded volumes for your areas of steep slopes and then apply a factor based on the grade of the slope to get more accurate volumes, but this would not change how it is displayed on the profiles and sections. And again not something I would usually bother with. Though it might make sense if your steep slopes account for a large portion of the design. But again, not dynamic. You would have to update your boundaries if the design changes.

You could also go down the route that @Joe-Bouza has indicated and just add additional vertical depth at the steep grade locations to approximate actual topsoil depth. But once again, not dynamic. You would need to update the boundaries if your design changes and the extents of the slopes change.

I will definitely be keeping one eye on this thread though, in case some of the guru's out there have a solution.....

Regards,

Peter

[neilyj666]

I think this is thoretically possible using the AutoCAD Surface tools BUT the number of triangles in a typical Civil surface will cause AutoCAD to hang. I think I have a note of the workflow on my PC at work so can't access at present.

EDIT: this thread message 8; https://forums.autodesk.com/t5/civil-3d-forum/offsetting-surface/m-p/7790582?collapse_discussion=tru...

This is a typical issue for landfill cell clay lining systems which are measured at right angles to the slope not vertically