Understanding Grading

Grading is the term that is most often used to describe the shaping of the land as a construction or design activity. From a design perspective, it is usually considered different than corridor design, which is also a form of terrain shaping but most often used for long, uniform, linear designs such as roads, channels, and so on. The term grading is typically used to describe shaping the land in small areas or modeling features that are not long and uniform.

The final product of a grading design will be a surface—the same type of object that you used to model the existing terrain in “Modeling the Existing Terrain Using Surfaces”. As you may recall, to create a surface representing existing ground (EG) elevations, you use breaklines drawn along linear terrain features such as curb lines, ditch lines, and so on. You can use the Civil 3D tools to make these breaklines from data collected in the field by surveyors. To create a design surface, you draw breaklines along curbs and ditch lines that are going to be built in the field. The process is fundamentally the same as creating an EG surface except that, in this case, the linear features are part of your design. For example, in Figure 17.1 you see the grading design for a pond represented by the red and blue contours. Civil 3D tools were used to draw the edges of this pond according to the required design specifications such as size, shape, depth, and so on. The objects representing the edges were then used to build a pond surface.

Figure 17.1  A grading design for a pond.