About Typical Cross Section

A typical cross section is the section that is created to scan along road/railway alignment (or its contour for the platform) to generate excavation/filling earthworks or subgrade layers.

It specifies:

• Excavation and/or filling profiles needed for earthwork and platform design,
• Subgrade layers needed for subgrade design,
• Earthwork surface in subgrade design if the earthwork surface is different from road/railway surface.

A cross section can be sketched-based, or UDF-based, detailed with tips in next paragraphs.

You can create a subgrade object type, and attach the typical cross section to it. Examples of subgrade and earthwork cross sections are available in the SubgradeTypicalCrossSections.3dxml stored in startup\Civil\Alignment.

The table below summarizes which cross sections are acceptable for different commands.

Cross Section	Subgrade Commands	Earthwork /Platform Commands
Sketched-based	Not accepted	Accepted
UDF-based	Accepted	Accepted

Here are the characteristics of the Sketch-based Cross Section:

• It contains only excavation and/or filling profiles.
• It can take parameters as inputs, it cannot take geometries as inputs.
• You must use the Cross Section Sketch commands to define excavation and filling profiles. The profile typing is automatically done with these commands.
• It is not mandatory to associate sketch-based cross section to an object type. You can directly select it in the earthwork/platform commands.
• A sketch-based cross section is much simpler to create than an UDF-based cross section. For an earthwork/platform cross section which does not depend on geometrical inputs, it is advised to use a sketch-based cross section.

Here are the characteristics of the UDF-based Cross Section:

The UDF-based cross section can contain the following definitions, as outputs of the UDF:

• Optionally subgrade layers, it can have as many subgrade layers as needed, used in the subgrade design.
• Optionally one excavation and one filling profile, used in the earthwork design.
• Earthwork surface cannot be specified explicitly. It is deduced from excavation and filling profiles: If they overlap, the overlapped area is used to compute the earthwork surface.
  
  

  Overlapped area.

  If excavation and filling profiles do not have an overlapped area, it can be used in earthwork command. But it cannot be used in subgrade commands for earthwork design.

The schema below illustrates about the structure:

Subgrade layer 1

Subgrade layer 2

Excavation profile

Filling profile

Each geometrical definition must be typed manually:

• The UDF outputs, called subgrade layers, must be typed as Subgrade Layer. They can be further typed by adding an Object Type of Subgrade Layer type. Typing is performed through the Define Specification command.
• The UDF output, the excavation profile, must be typed as Excavation works. Typing is performed through the Define Specification command.
• The UDF output, called Filling profile, must be typed as Filling works. Typing is performed through the Define Specification command.
• Note that there is no explicit UDF output corresponding to the earthwork surface.

It can take parameters and geometries as inputs. For example, the slope angle can depend on different terrain layer characteristics. The slope is almost vertical for a hard-rock layer, and much smaller for a soil terrain. An UDF allows to compute automatically these slope angles if the UDF takes these different terrain layers as inputs.

Table 1. Two ways of defining excavation and filling profiles

Type	Remark
Type A	Both excavation and filling profiles are continuous polylines. The excavation and filling profiles must be in contact. The shared common segment is used in the Subgrade commands to create a common surface, is ignored in the Earthwork commands. It is accepted by both the Earthwork and Subgrade commands.
Type B	At least one profile is a discontinuous polyline. The other one can be a continuous or discontinuous polyline. It is not mandatory for them to share a common segment but they must have shared points. If both profiles are discontinuous, it is not accepted in the Subgrade command. It is accepted in the Earthwork Design only.

If you define excavation and filling profiles with continuous polylines (Type A), such profiles can be used in both Earthwork and Subgrade commands.

Important: The rules for typical cross section valid for both subgrade and earthwork designs are: The cross section must contain a unique excavation profile and a unique filling profile. The excavation profile must be an open and continuous polyline curve, as shown in the left figure below. This is the same for a filling profile. Valid profile Invalid profile because it contains two segments which are not connected. The excavation and filling profiles must be in contact, as shown in the left figure below. The cross section in the right figure below is invalid, because there is no contact between the excavation profile and the filling profile. Valid profile: the excavation and filling profiles are in contact (the red line is to highlight the contact). Invalid profile because there is no contact between excavation and filling profiles.

If you define excavation and filling profiles with discontinuous polylines (Type B), such profiles can only be used in Earthwork commands. Subgrade commands cannot accept such profiles.

At least one profile is a discontinuous polyline. The other one can be continuous or discontinuous polyline.

It is not mandatory for them to share a common segment but they must have shared points.

It is possible to define shoulders in this type of profiles: The segment common to excavation and filling profiles is considered as a shoulder, as shown below:

Shoulders.

The internal points for each excavation and filling segments must be identical geometrically. The segments that are common to both excavation and filling profiles are considered as shoulders, in the same way as for a sketch-based profile.

The excavation and filling profiles must be defined as UDF outputs.

You can create a line linking the two internal points respectively on left and right sides of the cross section, and declare this line as the main result.

Earthwork Design commands only accept the UDF which contains excavation and filling profiles. If the UDF also contains subgrade layer definitions, they are ignored.

Subgrade Design commands accept the UDF which contains subgrade layer definitions and/or excavation and filling profiles of Type A. If subgrade layer definitions exist, the subgrade layers will be generated. If excavation and filling profiles exist, earthwork results will also be generated.