Smoothing a surface while retaining a minimum layer thickness problem

This question was posed to me today by Joe Torres - an interesting problem to look at

The problem is as follows. A landfill project, they have to build up the surface in layers. they just finished the previous layer and they had it surveyed and they now want to create a model for a machine that is exactly or as close to exactly 30cm thicker than the first surface vertically. The challenge is that the first surface has a lot of survey points and it is not totally smooth, and if they simply offset the surface and put that model in the machine, the machine blade is very erratic as a result.

So the request is to build a new surface that is smoother than the 30cm offset surface, but is a minimum of 30cm above the original survey surface - the material can be laid thicker than 30cm but not thinner, but the material is quite costly and the contractor only gets paid for the 30cm layer volume not what they put down.

I played about with various approaches to this and came down to the last 15 mins of this video - the whole video may be useful as there are tips on a variety of things in here, however I think the result achieved at the end of the video is close to the best that you can do, at least in the absence of the design model - if you have that then if you know that this surface is meant to be eg 60cm above the design, I would build that first, then see where the actual surveyed surface with the 30cm falls in relation to the design, find the points / areas that need to be raised based on the surveyed surface and just adjust those areas or make minor height adjustment to the entire surface until the highest points from the surveyed surface are covered - or make calls as to how you want to handle the high spots.

Having done all this - you could use the create surface grid command to create points at 1 or 2m centers - model those and then raise or lower that surface and it will create the same result and I think that is a smoothed surface that meets the criteria - if you need to adjust areas up or down to minimize additional material then you can raise or lower the points in the areas highlighted by a Cut Fill Map where the largest deltas lie.

Hope that this helps