What is Viability?
Viability describes the portion of your site where Level AI can produce a workable design. This depends on several constraints, such as existing ground levels, the design parameters you configure, and grading rules for roads, lots, grade breaks and other features.
Level AI begins by establishing a design envelope—the range of elevations between a minimum and maximum design surface. This range defines all valid levels that an area could potentially take given the input design parameters.
Areas where the minimum surface is below the maximum surface are considered viable.
Areas where the maximum surface is below the minimum surface are considered non-viable.
The “Design Envelope” is entirely determined by your input parameters and the existing ground that your design must tie into.
The Range Design overlay shows areas where the maximum surface is below the minimum (coloured by amount) - red areas have more non viability, blue are only slightly non viable. In this example the non viability is coming in from the edge of the site (the cross fall locks the road up), adding a grade break along this boundary (~2ft) would suffice to remove the non viability on a subsequent run.
Both the minimum and maximum surfaces are available in your DWG for inspection after a Level AI run.
Tip: You get a preview of the viability of your design mid-run by clicking on the run status either on allsite.ai or in Civil 3D (status pane).
Viability Percentage
Viability is expressed as a percentage of the total site area that is viable. Depending on the result, Level AI will follow one of two paths:
< 90% = “What-If” Mode
The model is not sufficiently viable to begin optimization. Level AI will instead test different design adjustments to improve viability and provide feedback on parameters you may want to tweak.NOTE - if What-if mode is not enabled the viability overlays are displayed but no what-if design is loaded into your DWG.
≥ 90% = Optimization Mode
Once viability reaches at least 90%, Level AI runs the grading optimizer. In this mode, the algorithms and AI models work to balance cut/fill earthworks, design compliant roads and lots, and produce the most efficient design possible.As there are still areas of non-viability that could affect your design compliance it's still good to review the viability overlay and run subsequent.
How to diagnose and correct areas of Non Viability
Working with 3D During Viability Checks
3D visualization can be helpful when reviewing parameters and diagnosing non-viable areas. However, it’s important to note:
In What-if mode, Level AI does not run the grading optimizer. The resulting 3D surface is a rough draft only—it may contain irregular break-lines, nodes, or other inaccuracies. Do not rely on this draft surface for decision-making or external use. It is intended for internal reference while you adjust parameters.
If a “What-If More Walls” result was generated, it only reflects the model’s suggestion to add more retaining walls. It does not incorporate other parameter changes you may need to make.
Adding Potential Grade Breaks to your model
You can add potential walls by selecting the POTENTIAL-GRADE-BREAK layer, selecting walls you want to add to your model and clicking Grading -> Grade Break to turn them into grade breaks in your model. You can then customize maximum heights, batter/slope width, etc.
Common causes of non-viability
Over constrained model - This is where there are too many grading restrictions added to the model such as:
Min/Max Elevation (parcels, ground controls)
Max Cut/Fill
Large Grade Change Existing Ground - Large grade changes will require grade breaks added, especially around the edge of the earthworks extent to allow existing surface to tie in with the proposed surface.
Grade break placement - Grade breaks will often be required at the interface with existing ground at the earthworks extent edge, also around lots if the lot grade is quite constrained with low grade on a steep site.
Building Placement relative to roads - Buildings (i.e. 0% grade) too close to a road can impact the roads ability to grade up.
Services - If you have Existing / proposed sanitary / storm networks in your model these could impact viability as they have a direct impact on the minimum surface. You can run with either Existing Services Only or Disable Servicing checks completely from your Level AI runs by adjusting the Level AI settings (settings pane in Civil 3D).