Sunday, September 26, 2010

Civil 3D Commercial Site Grading Plan Best Practices

Now that I have done a few grading plans with AutoCAD Civil 3D including an elementary school, a hospital, and a nuclear power plant, I'm at least at an intermediate level with the Civil 3D grading plan tools. So I figure I ought to stop and share tips from what I've learned so far. I'm sharing them in the form of a Best Practices list. I hope that you will take a moment to comment if you see that I have make a non-optimal conclusion about any of the listed practices.

Civil 3D Site Grading Plan Best Practices

Have a vision

Imagine preparing a grading plan without using a calculator. Imagine preparing a grading plan that yields earthwork estimates and staking information without additional data entry. Imagine preparing a grading plan that shows true contours all along the way for immediate quality feedback. Civil 3D fulfills these three visions.

Keep all intelligence in feature lines alone

The first lesson I learned in designing grading plans in Civil 3D was to consider the design surface as merely a draped throwaway object--merely a tablecloth over my design, with all grading intelligence resident in Civil 3D feature lines. This approach has a few implications:

1. You'll want to have a feature line at every labeled elevation on the plan. My first design was designed so that many of the spot elevations were simply floating between major feature lines, and when the contractor asked for tweaks to balance dirt, it was very hard to keep track of or to control the elevation changes at the floating points. This did not win me any points with the staking surveyor, who had already analyzed my first design.

2. When you add feature lines as breaklines to the design surface, you'll need to use uniform Supplementing factors so you can redo without anguish. The factors you choose are up to you, but I generally use 25' Distance and 0.05' Mid-ordinate distance. The 25' is arbitrary, and the 0.05' is somewhat less than the 0.08' minimum offset I use between feature lines.

3. In the event you need to export your design to another package, you will need to explode your feature lines to 3D polylines. This will destroy arcs, but if sending to Civil 3D, they can be reconstituted one at a time in Civil 3D using the Feature Line Fit Curve command.

Make selecting and snapping to feature lines easier

Sometimes you need to select feature lines or snap to their ends. To make this easy, use a complex linetype to make them visible. Also, be aware you can snap to spot elevation labels to get their elevation. I routinely snap to the Center osnap of my elevation labels that have Spot Dot circular markers.
This fence linetype makes it easy to select these feature lines.

Optimize your command workflow with toolbars or keyboard shortcuts

In grading design, you will find you use QuickEditFeatureElevs, OffsetFeature, and AdjacentFeatureElevsByRef, FeatureAddAsBreakline, CreateFeatureLines (from objects), Copy, Properties, Layiso, and Layuniso over and over all day long. And others of the Feature Line commands are common also. Optimizing the commands you use all day long makes the difference between tearing your hair out and grinning with glee. I suggest the following optimizations:

1. Have keyboard shortcuts. C=copy, FQ=QuickEditFeatureElevs, FO=OffsetFeature, FA=AdjacentFeatureElevsByRef, FCO=CreateFeatureLines (from objects), FAB=FeatureAddAsBreakline, etc. See my previous post for more information.

2. Optimize your access to the Properties palette. Have it continually open or anchored Left or Right with auto-hide. You will use this to change the display style often for your surface and your copied surface Spot Elevation Labels and Slope Labels.

Add and update design surface and labels early and often

It's no fun to design blind. Get immediate feedback by turning on Automatic rebuild for your design surface and adding/copying slope and spot elevation labels (see my posts on spot elevation label styles and copying them). Also add new feature lines to the design surface as breaklines in frequent groups as you proceed.

Lots of elevations and slopes during design

Draft as you design

Consider the finished scale and view rotation of your plan before you start, and work with it as you design so that your label placements may be xref'd into your final plan. With regard to contour labels, keep in mind that you will likely end up labeling dedicated landscape/basin surfaces rather than the entire design surface, so label them on the design surface only as required for design.

Be judicious about live Projection Gradings

If you read Civil 3D help carefully, it becomes obvious that projection gradings are bona fide computationally difficult objects. Because of that, they are prone to cause drawing instability, and experience bears this out. Each version of Civil 3D brings increased stability, and there are simple cases where projection gradings are a simple calculation. But be alert to the need or prepared to save a copy of your design drawing to perform Projection Gradings, then explode them to 3D Polylines and bring them back into your live design drawing.

Save, audit, and backup often

As alluded to in the previous practice, drawing errors are an ever-potential problem. Use a custom shortcut to save snapshots of your drawing often.

Have a range of contour styles

It's often helpful to see contours with an interval much less than a foot during design. On the other hand, invariably during design, the end of a feature line will acquire a zero elevation, which will immediately generate thousands of tightly packed contours around that point. At those moments, you may be grateful to change to a style that shows contours with an interval of 100' or more while you fix the mistake.

Model curbs minimally, but accurately

TC-based elevations at left; P-based elevations at right.  Note gaps at corners.

A. For the typical curb situation, you need two feature lines for grading design: 1) the front/bottom/lip of the curb where pavement typically begins and 2) the top back of curb line where sidewalk or landscaping typically begins. Be sure to set the elevation difference between these to account for both curb height and gutter depression. The other lines (gutter and top face) between those two are only needed occasionally, or for last minute looks. Set up your label styles to look at top of curb elevation and calculate an appropriate drop for the associated gutter elevation label. Then label back of curb endpoints.  Or for single curb or if you can live with curb labeled at the lip of gutter, set up styles to look at pavement elevation and calculate the appropriate rise for top of curb.

B. In most cases, you can proceed through final design without ever drawing the troublesome curb corners at parking lot corners. Instead, simply offset lip of gutter (edge of pavement) back and up to make back of curb, leave open the gap created at parking space corners, and label either nearby back of curb endpoint in place of the missing corner point (or the actual lip of gutter corner if you are using that approach).

C. Remember that you may not need feature lines that accomplish nothing other than describing concrete details.  For example, if your labels are based on pavement elevation, you may not have any need for top/back of curb feature lines along landscaped areas.  Instead of creating feature lines for top/back of curb in those situations, offset the pavement feature line to the nearest landscape hinge point.

Answer design standard questions before starting

It's inevitable with 3D drafting that some questions about design standards will arise that you probably never considered before. Prepare yourself and your team to answer these questions promptly and authoritatively. Examples:
1. What kind of offset (distance and grade or difference) will you use from objects (fences, buildings, curbs, slabs, paths, footings) to tops and toes of steep slopes?
2. What relative elevation should landscaping be next to sidewalks and curbs in your model?
3. Will you use ADA maximum slopes (2%, 5%, 12:1), or some near approaching slope?
4. Will you model rough grade or finished grade in landscaping? What's simplest? Can it work for you? In my experience finished grade has worked fine.

Broad brush your outline quickly, then gradually fill in the detail

1. Often you can begin your design by drawing or copying a rough estimate of the limits of grading, assigning it to the existing ground surface allowing "Insert intermediate grade break points", and adding it to surface "FG". Then, for lack of a better idea, you might create a few other major lines assigned to surface "FG" without allowing "Insert intermediate grade break points" (since you want idealized design features).
2. Design outer parking perimeter first and necessary walks to obtain building elevations, then add major warp (ridge and valley) lines, and assign island and bullnose elevations from the resulting surface automatically later.
3. Be aware of the potential effect of ADA ramps on your design, but don't design ADA ramp detail until and unless you need it for your calculations or presentation.
4. Use projection gradings in a copy of your design drawing (or an empty new drawing) to grade landscaped areas, or simply add arbitrary feature lines and tweak them using grip editing and FQ=QuickEditFeatureElevs with several precise slope labels until you like the slopes and contours you see.

Don't be afraid to grade by gut feel

Since you are no longer using a calculator, and you have the immediate feedback of contours and slope and elevation labels, it's natural and perfectly okay to iteratively experiment with slopes using FQ=QuickEditFeatureElevs and grip editing (in landscaping) until you like the results. As long as you use a liberal smattering of (temporary) One-point slope labels and a few appropriate Two-point slope labels at flowing curbs/gutters/ditches, you will be safer than you ever were before with a calculator.
Lots of slopes plus contours tell the truth about your design

Offset building footprints inward

Around a building, you need to model lots of grading action against the stem wall. But you also need to preserve the finished floor elevation. Offset the true finished floor inward (less than a wall thickness if the footprint doubles back on itself in places; I use 0.1' to 1') to represent the finished floor, then grade the outer feature line as required.

Use dedicated surfaces to show contours in scattered areas

During design you will want to have lots of contours showing.  But for presentation, you may want contours showing only in certain areas.  The way to do this is to create a dedicated surface for each isolated area of contours.  Paste the design surface into the dedicated surface and add the required boundary.  Then add contour labels to the dedicated surface.

And now a conscientious plea:  Find your family members and give them a hug.  Get all your money and move it from stocks and banks to a credit union.  These things matter.


Lynda said...

Having prepared thousands of grading plans I would appreciate the opportunity to view one of yours, preferably for a commercial development. Thank you,

Thomas Gail Haws said...

Well, Bill. It has been a while, but I've added a snapshot for you to look at. Let me know if you'd like to see anything else.

Anonymous said...

I am working on a development site with anchor stores and pad sites on about 22 acres. Each pad site and anchor store area has parking lots, islands with planters, curb, gutter and textured sidewalk. I want to have the ability to construct the civil portions ( parking, islands, curbs, roads etc. in Civil 3D and/or Revit) I them want to add trees etc. for a complete 3D model that can be rendered for the local planning authority and client. The current method in Civil 3D is very convoluted and is a time waster, to provide a completed grading design of a building, parking lot, curbs, sidewalks etc. and entrance roads .

Do you know of an add on program that can help expedite the insertion of such site elements easily, effectively and quickly that can be fine tuned and adjusted for a complete final design without all the convoluted steps?


Thomas Gail Haws said...

I don't know of any program like that, but I think my Autodesk reseller has been promoting something along those lines. You might talk to an Autodesk reseller for ideas.