Grading is certainly one of the toughest challenges in civil engineering design, regardless of which software you’re using. I’ve got a few simple rules that I live by when grading that keep me from pulling my hair out when changes arise or when I run into obstacles.
1. Work in Stages
It’s tempting to just jump right in and start setting elevations on all of the curbs, methodically working your way around the site. You may get lots of work done, but nearly all of it will have to be redone if something changes.
Think of the way a sculptor would create a bust from a block of stone. He or she would first chisel out the basic shape of the subject and then add more and more detail until the design is complete. The sculptor wouldn’t start by carving in the eyelashes.
Stress-free grading should be done the same way. Start out rough and simple, building something that can be rebuilt in a few minutes. Then drive the next, more detailed iterations using this general model. The Elevations From Surface command is a great way to bridge the gap between each iteration.
The following image is a rough grading model which is simply a rectangular panel that slopes in a certain direction at 2% It was built from one feature line and two grading objects. Although it’s shape is simple, it represents all of the elevations for the entire site.
2. Work in Sections
Grading the entire site at once could put you in a straight jacket. Don’t try to grade the parking lot, pond, entrances, and retaining walls in one massive system. Instead, design each one separately and tie them together. The ability to paste surfaces is a great tool for this approach.
The entrance shown below was built separately as a corridor and ties into a composite surface made up of EG and the parking lot grading.
3. Don’t Make it More Difficult Than It Is
Not every grading solution requires the use of grading objects. I was once helping out a designer who had spent hours trying to create a grading object that would tie from the back of a parking lot curb to the exact location of the property line. When she asked for my advice, I said to erase the grading object, draw a feature line along the property line at existing ground, and simply let the surface triangulate the space between. It was a 5-minute solution.
So keep these tips in mind the next time you perform grading with Civil 3D. It’ll help you keep your hair and keep your stress level down!