The profile shows how the road rises and falls along its length. To see how it sits on the ground at each point you have to cut across it: where the pavement is relative to the ground, how long the slopes are, whether it is in cut or fill. That is a cross section, and a road package holds dozens to hundreds of them.
This article builds Civil 3D cross sections from an existing corridor. It covers three jobs: placing sample lines at stations, batch-creating section views, and reading cut and fill sections. The alignment and corridor come from Civil 3D corridor.
Cross sections and sample lines
A cross section is a vertical cut perpendicular to the centerline at one station. The horizontal axis is offset left and right of the centerline, the vertical axis is elevation. It shows the existing ground and the design section: pavement, shoulders, ditches, slopes.
In Civil 3D the cut position is a sample line: a line across the alignment with a station and a swath width each side. Each sample line samples every source you choose: existing surface, corridor, design surfaces. The results are sections, drawn inside section views.
| Object | What it is | Here |
|---|---|---|
| Sample Line Group | All sample lines of one alignment | CAT NGANG TUYEN CHINH |
| Sample Line | One cut position | 31 stations from 0+000 to 0+461 |
| Section | One source's cut at one station | Ground and corridor |
| Section View | The gridded frame showing sections | 31 views |
Sample lines are also the basis for cut and fill volumes by the average end area method. This is practised in full in the Institute's online Civil 3D course.
Step 1: Batch-create sample lines by setup
On the Home tab, Profile & Section Views panel, click Sample Lines, or type CREATESAMPLELINES. The command asks for an alignment. Press Enter to pick from a list, choose TUYEN CHINH and click OK. The Create Sample Line Group dialog opens.
| No. | Item | Meaning |
|---|---|---|
| 1 | Name | Group name, e.g. CAT NGANG TUYEN CHINH |
| 2 | Sample line style | How sample lines look on the plan |
| 3 | Select data sources to sample | Sources to cut: surface DIA HINH TU NHIEN and the corridor, both ticked, Dynamic update |
| 4 | OK | Create the group and open Sample Line Tools |
Check the source list: if the corridor is missing, sections will show only the ground. Build the corridor first, or add it later with Sample More Sources.
Click OK and the Sample Line Tools toolbar appears for placing stations.
| No. | Item | Meaning |
|---|---|---|
| 1 | Sample line group | The group receiving new sample lines |
| 2 | Creation method | Click the arrow to choose how to place them |
Choose By range of stations... to place them at a regular interval.
| No. | Property | Meaning |
|---|---|---|
| 1 | Left Swath Width | Cut width left of the centerline, set to 25 m |
| 2 | Right Swath Width | Cut width right, set to 25 m |
| 3 | Increment Along Tangents, Curves, Spirals | A 20 m station interval |
| 4 | At Range Start, At Range End, At Horizontal Geometry Points | Set to True to add the start, the end, and the PC and PT stations |
The swath width must cover the whole slope. At the deepest cut of the sample route the slope reaches about 16 m from the centerline, so 20 m is tight and 25 m is safe.
Click OK and press Enter to finish.
| No. | Area | What it shows |
|---|---|---|
| 1 | Start of route | Even stations 20 m apart, labelled 0+000, 0+020... |
| 2 | End of route | The end station 0+461.01, added by At Range End |
The sample route gets 31 sample lines: 24 even stations, the start, the end, and the PC, PT and mid-curve stations of the two curves.
Step 2: Create the section views
On the Home tab, Profile & Section Views panel, click the arrow next to Section Views and choose Create Multiple Views.
| No. | Item | Meaning |
|---|---|---|
| 1 | Section Views button | Opens the menu |
| 2 | Create Multiple Views | Builds views for the whole group |
The Create Multiple Section Views wizard has seven pages. The one to check is Section Placement.
| No. | Item | Meaning |
|---|---|---|
| 1 | Section Placement | The placement page |
| 2 | Draft | A grid in model space, handy for checking. Production places views straight onto sheet frames from a template, for drawings |
| 3 | Create Section Views | Build the views, then pick an empty point for the grid corner |
Civil 3D builds 31 views, each titled with its station. The wizard also has Offset Range and Elevation Range pages to set the width and datum for the whole group as it builds; step 3 below adjusts individual views afterwards.
Step 3: Set the datum and width of the view
Two settings decide how a section view looks:
- Datum: the elevation of the bottom grid line, the Minimum of the view's elevation range.
- Width: how far left and right of the centerline the view extends.
Open one of the views. If it has a grid and axes but no ground line, its elevation range does not contain the section.
On the sample route the ground is at 19–33 m, but the batch-created views took a range around 0 m, so every section fell outside its view. To check, select the view and click Section View Properties on the contextual tab.
The Sections tab shows whether the sections hold data.
| No. | Item | Meaning |
|---|---|---|
| 1 | Two section rows | Ground DIA HINH TU NHIEN and corridor. Draw ticked means drawn. The last column gives each section's lowest elevation |
The sections hold data, so the fault is the elevation range. On the Elevations tab choose User specified and enter a minimum and maximum that contain the section.
| No. | Item | Meaning |
|---|---|---|
| 1 | Elevations tab | The view's elevation range |
| 2 | User specified | Minimum 26 m, maximum 40 m: the lowest elevation from the Sections tab minus 3 m, the highest plus 3 m |
Click OK and the section appears, with a 26 m datum.
The width is set on the Offsets tab. Automatic uses the sample line's swath width, 25 m each side here. At 0+340 the right slope only reaches about 17 m, so the view can be narrowed to 20 m each side for a tidier sheet.
| No. | Item | Meaning |
|---|---|---|
| 1 | Offsets tab | The view's width |
| 2 | User specified | Left −20 m, Right 20 m. The width must contain the toes of slope or the slopes are cut off at the view edge |
Step 4: Set up cut and fill areas on the cross sections
Cut and fill areas on a section come from a material list, created with Compute Materials once a corridor surface exists; the steps are in Civil 3D earthwork volumes. After computing, each station gets two material sections: cut and fill.
Reopen the view's Section View Properties, Sections tab.
| No. | Item | Meaning |
|---|---|---|
| 1 | Two Material List rows | The 0+340 material sections. Tick Draw to show them in the view |
| 2 | Style | Cut Material for cut, Fill Material for fill. Change them here to colour or hatch cut and fill to your drawing standard |
To print the area figures on the section, go to the Volume Tables tab.
| No. | Item | Meaning |
|---|---|---|
| 1 | Volume Tables tab | Material tables attached to the view |
| 2 | Type, Select table style | Choose Material and the Basic table style |
| 3 | Add>> | Adds the table and opens Select Materials |
| 4 | New table row | The table reads Material List - (1), updated Dynamic |
| No. | Item | Meaning |
|---|---|---|
| 1 | Ground Removed, Ground Fill | The cut and fill materials of the Cut and Fill criteria. Tick both and click OK |
The Position settings place the table beside the view: Section view anchor Top Right and Table anchor Top Left attach the table's top-left corner to the view's top-right corner. Click OK.
The table is drawn at the drawing's annotation scale. At the plan's 1:1000 it is several times larger than the view. Set the annotation scale on the status bar to 1:200, the usual cross-section scale, and the table fits beside the view.
| No. | Item | Meaning |
|---|---|---|
| 1 | Area column | Cut area 53.92 m², fill 0.00 m² at this station. Volume is the quantity since the previous station, Cumulative Volume the running total from the start |
| 2 | Cut material section | The red outline is the cut between existing ground and the underside of the road structure |
A table added in Section View Properties attaches to that view only. For tables on every view, run Compute Materials before building the views and add the table on the Section View Tables page of the Create Multiple Section Views wizard.
Step 5: Read cut and fill sections
At station 0+340 the design is about 2.5 m below ground, so the road is in cut:
- The white line is existing ground, rising left to right because the station is on a hillside.
- The heavy white line in the middle is the two-lane pavement, 3.6 m per lane at 2% each way.
- The blue lines on each side are the ditches, then the cut slopes climbing to meet the ground.
- The right slope is much longer than the left, because the ground is higher on that side.
At station 0+160 the design is about 1.5 m above ground, so the road is on fill. The pavement sits on a trapezoidal embankment whose slopes run down to the ground. There is no ditch, because the side-slope subassembly chooses cut or fill at each station from the ground.
The cut and fill areas on each section, multiplied by the distance between stations, give the earthwork volume of that stretch.
Common problems with Civil 3D cross sections
Empty section views. The view's elevation range misses the section, as in step 3. Check the Sections tab first: if there is data, fix the Elevations tab; if not, check the group's sampled sources.
Only ground, no pavement. The corridor is not a sampled source. Select a sample line, click Sample More Sources and add the corridor.
Slopes cut off at the view edge. The swath width is shorter than the slope. Increase the Left and Right Swath Width.
No stations at curve start and end. At Horizontal Geometry Points was not enabled. Add them with the At a Station method, or delete the group and recreate it.
Corridor edits do not show. The section Update Mode is Static. Set it to Dynamic in Sample Line Group Properties, Sections tab.
Frequently asked questions
What station interval is enough?
Road packages usually use 20 m or 25 m even stations plus special stations at curve points and sudden terrain changes. Closer stations give more accurate volumes.
How does a Section View differ from a Section?
A section is one source's cut line at one station. A section view is the frame with grid, axes and bands in which those sections are drawn.
How do I turn cross sections into sheets?
Choose Production on the Section Placement page with a sheet template. Civil 3D places the views onto sheet frames, and Plan Production creates the layouts.
Can I label offsets and elevations on each section?
Yes. Section view styles and band sets add offset and elevation labels at grade breaks, and a band under the view can list ground and design elevations at fixed offsets. Set them once in the band set and every view in the group picks them up.
Why do some sections show a ditch and others not?
The side-slope subassembly checks the ground at every station. Where the design is below ground it builds the cut branch with a ditch; where it is above ground it builds a fill slope without one. The choice is made again whenever the corridor rebuilds.
What comes after cross sections?
Compute cut and fill per station with Compute Materials on the sample line's contextual tab, then export the volume table.
Related articles
Cross sections are the fifth link, after contour lines, Civil 3D alignment design, Civil 3D profiles and Civil 3D corridor. Autodesk's overview is in About Sample Lines.
Cross sections with superelevation, junctions and station-by-station quantity tables are session 5 of the Institute's online Civil 3D course.