This question came in today so I figured I would record a video covering the details as it has a few complexities that are worth looking at and it requires the use of the Overexcavation Template function to get the desired results.
In the example the user was doing a Takeoff that included a number of concrete tanks that have a 12" concrete base on 4" Polystyrene insulation on top of 12" Crushed Aggregate Stone. The design calls for a 5’ overex below Finished Grade (32" below subgrade) to take care of ground frost below the tank.
The tank design called out that the aggregate base needs to extend 2 feet beyond the edge of the tank and that the polystyrene foam extends a further 2’ beyond that as shown below.
The challenges normally associated with subgrade adjustment are that they are applied vertically within the polygonal area in which they are defined. So how do you model and compute the volumes for the edge details at the same time as using the overexcavation functions.
The second challenge is with the overex, that is computed typically at 5’ below finished grade / subgrade so in the area outside the pad, 5’ would be computed below the FG surface, whereas in the area under the pad it would be computed 5’ below base of subgrade vs 5’ below finished grade. Doing that will create a step the depth of subgrade where the overex base crosses the building pad line. So how to work around that? This is where the overex Template function assists you, you can compute the overex using the pad line itself, that will cut down a depth below base of subgrade (so with the subgrade being 28" (12" 4" 12" materials) you need to Overex a further 32" below that to get the 5’ overex called out in the design. From that line you simply create an overex template that has a 4’ offset at 0% slope or 0 elevation difference followed by a daylight tie up. The daylight tie up will stop at whichever of the following it hits first
- Finished design
- Finished design with subgrades adjusted
- Original ground
If in cut it is likely the overex daylight will hit either 1 or 2 above first. If in fill it is possible that it will hit 3 first.
The video below shows you how to handle this