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Why does the roadbed slope come out vertical?
Summary
When defining the roadbed layers of a template in MDT, the outer slope of those layers may come out vertical instead of inclined. There are several different reasons for this: in some cases it is a design limitation (when the slope or the ditch starts from the head of the roadbed, the roadbed slope is always vertical), and in others it is down to a specific setting of the roadbed criteria or of the outer slope values (Slope E.L. and Slope E.R.). This article explains how to tell each situation apart, how to give the roadbed slope the inclination you want when that is possible, and where the "vertical" behaviour of the cut is actually controlled when measuring roadbeds.
If the roadbed slope is the one you want but what does not add up is the measurement —the measured area does not match that of the cross sections, or an extra roadbed wedge is measured—, the article you need is «Roadbed measurement: vertical cut and slope wedge» (📁 10.MEASUREMENTS).
Applies to
MDT — Templates and roadbeds module. The documented cases do not indicate a version number; the Slope E.L. and Slope E.R. parameters of the roadbed layers are still current in MDT 26, according to its reference manual.
Roadbed definition in templates: roadbed criteria and Slope E.L. / Slope E.R. values.
Symptoms
When creating the roadbed layers of a template, an inclined slope cannot be applied and the slope always stays vertical.
When defining a roadbed that includes a "selected" soil layer, the slope generated in the fill comes out vertical instead of with the expected inclination.
When running the volume calculation, the "Vertical slopes" option for configuring the cut calculation in roadbed measurement cannot be found.
Doubts about which roadbed criteria to use ("Variable" versus "Adapt layers") and how it affects the result.
Cause
An unwanted vertical slope may be due to different reasons depending on the case:
Slope or ditch starting at the head of the roadbed: when the slope or the ditch starts from the head of the roadbed, the slope of the roadbed layer is always calculated vertically. This is a design limitation of the program, not an error.
"Variable" roadbed criteria wrongly set: if the roadbed criteria is set to "Variable" and the values of Slope E.L. (exterior left) and Slope E.R. (exterior right) are fixed at 0.01, the resulting slope is practically vertical.
Confusion about where the vertical cut is controlled: the slope option in the roadbed calculation is not managed from the volume calculation command, but from the template / roadbed definition itself.
Solution
Case: the slope stays vertical because the slope or the ditch starts at the head of the roadbed
In this configuration it is not possible to give the roadbed slope any inclination:
If the slope or the ditch starts at the head of the roadbed, the roadbed slope will always be vertical.
This is a design limitation of the program, not an error. If you need an inclined roadbed slope, review how the template is built so that neither the slope nor the ditch starts from the head of the roadbed.
Case: unwanted vertical slope in fill with the "Variable" roadbed criteria
When the subgrade has to be superelevated and the slope comes out vertical because the criteria is "Variable" with the outer slopes at 0.01:
Go to Templates > Create / Edit and move to the Roadbed tab.
Change the Roadbed criteria from "Variable" to "Conditioned".
In "Pend./Cond." set the value 10. This ensures that the subgrade stays superelevated unless that value is exceeded, in which case it will be parallel.
Set the Slope E.L. and Slope E.R. values to the slope you actually need (for example, 1.5) instead of leaving them at 0.01.
With this configuration the template is built with the slope inclination defined.
Case: the "Vertical slopes" option does not appear in the volume calculation
The option that makes the roadbed cut vertical is not in the volume calculation command, but in the roadbed definition:
Go to Templates > Create / Edit and open the Roadbed tab.
In the Slope E.L. and Slope E.R. fields set the value you want. For example, 0.01 produces a practically vertical slope.
Then recalculate the roadbed.
They are the same two fields used in both directions, depending on what you are after: 0.01 so that the roadbed cut comes out vertical (and the roadbed slope wedge is not measured), or the actual slope of the roadbed —1.5, for instance— so that the template is built inclined and the measurement takes the spill into account (see the previous case, on the "Variable" criteria).
What the vertical cut implies
When a roadbed layer is measured with a vertical cut, the material is measured with a vertical cut on both sides at each station. This may mean that the actual spill of the slope is not taken into account and that the measurement does not match that of the cross sections. Adjust the roadbed slope values according to whether or not you want to reflect that spill.
Case: difference between the "Variable" and "Adapt layers" roadbed criteria
To choose the right criteria when defining the template:
"Variable" criteria: the subgrade is defined in a fixed way by means of vectors.
"Adapt layers" criteria: the subgrade takes the shape resulting from applying the thickness of the roadbed layers defined.
If the problem persists
If the slope still comes out vertical after reviewing the roadbed criteria and the outer slope values, check that neither the slope nor the ditch starts from the head of the roadbed (see the first case), since in that situation the roadbed slope is vertical by design.
In complex templates with many assignments, the APLITOP support team can review the particular segment: attach your segment when opening the enquiry.
Category: Templates and roadbeds · Level: Intermediate