When working with pipe rules, specifically the cover & slope rule, you may be surprised with the end results after drawing your network, or applying the rules. There is quite a bit going on in the background when this rule gets applied, so after this is understood you may have a clearer picture of the results that are shown in your design.
When run, the cover & slope rule performs the following steps:
1. Upstream invert elevation is set based on the cover at the structure.
2. Downstream invert elevation is set based on cover at the structure.
3. Slope is checked:
• Minimum slope violation: upstream invert elevation is held>minimum slope applied
• Maximum slope violation: Flagged as violating maximum slope
4. Cover is check along entire length; 1/3 rule is applied:
• If a violation is found within the first 1/3 of the length, downstream invert is held, upstream invert is lowered.
• If a violation is found within the middle 1/3 of the length, pipe is lowered to satisfy minimum cover at low point, slope should remain the same
• If a violation is found within the last 1/3 of the length, upstream invert is held, downstream invert is lowered.
5. Slope is checked again:
• If minimum slope is violated, upstream invert is held. Downstream is lowered to achieve minimum slope
• If maximum slope is violated by constraints within the structures or by a user’s edits, violation is flagged and slope remains unchanged.
As you can see quite a few operations are happening in the backgrouns when this rule is run. Please note the underlined steps above in which maximum slope violations will just be flagged. These will not be altered by the rule, and will need to be manually edited if there are any violations detected. Hope this helps!