Balance Cut Fill for elevated pads

Hi Alan,

I’ve just watched your ‘Elevate Pads for Subdivision’ clip and would like to know if it’s possible to automatically calculate an elevation for each pad that will balance out the Cut and Fill amounts given a start surface?


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Each pad individually - ie

Pick your pad (elevated line or pad surface) - does that have cut and fill slopes to tie out?

Pick your reference surface (existing terrain)

Raise / Lower the pad - if sideslopes involved recompute them for each elevation change until you get Cut = Fill to within a tolerance band eg 1% delta

Report the pad Z change needed to get a balance and the Cut / Fill values at that point and allow user to make the change permanent.

Is that what you are asking for?

We can do this partially by creating the pad and sideslopes and then compute the isopach surface and on that create smart text that has the Cut and Fill and Balance volume in the smart text. Then you can see the balance and raise or lower the pad line using change elevation and the sideslopes are recompiled and a new balance displayed. You can repeat the process until you get what you need for the balance.

Not automated but it works today. The isopach surface properties has the source and target surfaces so you can change them to compute different pads.

Because on a large subdivision the pads have to interact with each other and the existing it is not so easy typically - however on a commercial site I could see more value because each pad tends to be a little more isolated

What is your application?


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Thanks Alan, now I have to think…sorry if this reply rambles on,

So my new client has supplied me with a start surface and a 2D Lot model, similar to your example, only he doesn’t know the pad levels - he want’s me to determine them by balancing the cut/fill for each lot independently. I’ve been asked to supply a cut fill plan and volume report for each Lot that balances as you’ve described - to within a certain error band as I can’t imagine it needs to be too precise. They’re also talking about benching and crossfall on the pads but I think that’s pushing they’re luck and something that can model up separately.

I don’t think a side slope is necessary, at least for my requirement and I really liked the offset line option available already. I does a beautiful job of cleaning up the strings and surface. A side slope option might be helpful as mentioned with single pads but I envisage a whole world of pain with overlapping strings when you have multiple pads.

In our other program (very very similar to, but not necessarily 12d) there’s a macro available that runs an iterative process to adjust the pad levels as required. I haven’t used it for years and need to check if you need to enter at start design RL first or it’s calc’d but it’s something like this;

  • User selects a closed polygon and enters side slope or maybe an offset value.

  • Used selects a start surface (assuming start surface covers entire area)

  • Program takes a sample of the start surface and established a mean elevation as it starting level or user entered. Program makes a temporary surface of the ‘design’ level.

  • User enters and step up / down value. i.e. 0.1m for iterations.

  • Program runs a quick start surface to ‘design’ surface with boundary, calc’s and steps up or down to run again until it hits the mark. Maybe round the design level to the nearest step value to get a nice even number?

  • Surveyor goes to pub to check some fluid levels and lets computer run.

If it worked and could chuck out a text report or smart text as described with the volumes then yes, the user could accept and make permanent.

I don’t do any subdivision design (yet) so I’m not sure how others calc this? There must be an automated way for large jobs I would think or a bit of ‘suck it and see…’

I’ll play around with the isopac method described above as that sound pretty cool.