What is the difference between "Pipe Crown" and "Pipe Soffit" in the dropdown for "Measure Cover To" in the Cover tab of the Design Alternative?
The "Measure Cover to" option in the design constraints dialog refers to the depth of fill above the pipe top. Selecting Soffit means that the cover is measured as the distance between the top of the inside of the pipe to the ground elevation. Selecting Crown means that the cover is measured as the distance between the top of the outside of the pipe to the ground elevation.
In most cases the difference may be quite small; equal to the wall thickness. The option was added along with the introduction of the Wall Thickness input in the Conduit catalog and some users may prefer one way over the other, so we provide the option.
Note that the Design constraints are used with the Design Calculation Type with the GVF Convex or GVF Rational solvers. Cover constraints are typically used to ensure an adequate depth of fill on top of the pipe, but too deep and excavation costs can be a concern.