A grade break informs Level AI where a split can be added into the model, this can either be a slope with a grade or a wall. Whether it is a wall or a slope depends on the grade break settings. Wall setting default values are inherited from the projects web settings. Level AI will put a slope if the parameters (height, width) allow, if there would be a clash with another object (i.e. a pond, building, other grade break, road, earthworks extent) it will flip to a wall.

Grade Break Angle Requirements

Grade breaks that form retaining walls should not contain sharp corners or cross other grade breaks at sharp angles. The inside angle is measured at each corner, where 180° is straight and smaller angles represent sharper turns.

60° or greater: Accepted.
10° to less than 60°: An information note is displayed, and the Level AI run continues.
Less than 10°: A warning is displayed, but the run is not blocked.

Level AI Prepare fixes most sharp corners itself before it checks them. It removes a corner of less than 5°, cuts back a corner of less than 40° by 2 m (6.5 ft) along each side, and joins two grade breaks that meet at less than 40° as a T. Each grade break it changes gets an AutoFix_WallAcuteAngle review so you can check the result. Running validation on its own in Civil 3D does not apply these fixes, so it can still report corners that Level AI Prepare would fix.

If an angle warning remains, adjust the grade break segments so the angle is at least 60°. This check applies both to corners within one grade break and locations where separate grade breaks intersect.

Grade breaks can be manually drawn, or added from the automatically generated "Potential Grade Breaks" after a Level AI run.

Drawing a Grade Break

Select "Grade Break" from the Grading Draw/Convert menu, you can now customize settings for the grade break.

The Allsite Draw/Convert panel with the Grading dropdown open and Grade Break outlined.

Animated walkthrough of adding grade breaks to a DWG in Civil 3D

Grade Break Default Settings

Default settings are configured in the web, these are initialized on project creation from a close project / specific client project and can be subsequently updated. Default settings apply to all walls when they are created in Civil 3D.

Setting	Description
Retaining walls allowed	If deselected, maximum batter width will dynamically be updated to max height / max batter grade. The grade break will still flip to a wall if there is not room for the desired slope.
Max height	Default maximum height the grade break can be.
Max batter grade	Default Batter / Slope maximum grade
Max batter width	Default Maximum width before grade break flips to a wall.
Minimum draw height	The minimum height to draw a wall (smaller than this will be excluded)
Retaining / Batter Slope Design Table	Defines where the wall's (or batter/slope's) feature lines sit relative to the 2D grade break line. Each row is a height, and values between rows are interpolated by the wall's designed height. Wall width: the horizontal distance across the wall, between its high-side and low-side feature lines. For a batter/slope, the width is its height divided by its maximum batter grade. Drainage offset: the gap between the grade break line and the wall when the line is on the wall's high side. Toe offset: the gap between the grade break line and the wall when the line is on the wall's low side. The offsets apply to walls with Snap Direction LEFT or RIGHT. A wall with Snap Direction CENTRE straddles the line and uses neither.

Grade Break Settings

The following settings can be customized per wall

Setting	Description
Max Height	Maximum height the grade break can be.
Max Batter Grade	Batter / Slope maximum grade
Max Batter Width	Maximum width before grade break flips to a wall.
Minimum Height to Left	This creates a 'fixed offset' grade break and can be used for truck-bays or walk-out basements where the direction and minimum height of the grade break are critical. For this type of grade break, it specifies a minimum allowed height of the wall in the 'left' direction (line style indicates which side of wall is 'left'. Leave blank in most cases. If using Minimum Height to Left, ensure the max height is set to 2-4 inches higher to allow for Level AI to iterate the design surface.
Allow Wall	Whether this grade break may become a retaining wall when retaining walls are turned off for the project. Filled from the Retaining walls allowed setting.
Snap Direction	Which face of the wall sits on the drawn line: LEFT or RIGHT of the direction the line was drawn, with the wall built out to the other side, or CENTRE (the default) to keep the wall on the line.
Type / Sub Type	Where the grade break sits relative to the lots, for example FRONTAGE_WALL / ROAD_FRONTAGE. Filled in on potential grade breaks and kept when you convert one; see Potential Grade Breaks below for the values. Leave them as None on a grade break you draw yourself.

For example if maximum height is 6ft, batter grade is 33% and maximum width is 9ft, then if Level AI sizes grade break up to 3ft in height grade break will be a slope, and anything between 3-6ft will be a wall.

When using Minimum Height to Left, be aware that this can cause runaway in your model as the grade restriction can effectively 'fight' other grading constraints in your model. Ensure the Max height is at least 1ft higher than the min height and ensure the direction is correct.

Potential Grade Breaks

On a parcel you can configure the vehicle crossing placement and width on each Parcel Object. Alternatively driveway crossings can be specified by drawing an Impervious feature and setting the type to DRIVEWAY. The Potential Walls settings on the Retaining Walls / Grade Breaks settings page control where potential grade breaks go: Add potential walls around roads and Add potential walls at front of property (both on by default), and Snap direction of walls on adjacent lots (HIGH by default).

Potential grade breaks are generated on every Level AI run. Layout Assist also generates them when Generate potential walls is turned on in the Layout Assist settings (it is off by default). Each potential grade break gets a Type and Sub Type that say where it sits:

Type	Sub Type	Where the potential grade break sits
FRONTAGE_WALL	ROAD_FRONTAGE	Along a lot's road frontage, with a gap left for the driveway crossing.
INTERNAL_WALL	SIDE	On a boundary between two lots that meets an end of the lot's road frontage.
INTERNAL_WALL	REAR	On a boundary between two lots that does not touch the road frontage.
EXTERNAL_WALL	EXTERNAL_BOUNDARY	Along the edge of the site (the lots and roads together) wherever that edge is within 20 m (66 ft) of the earthworks extent.
INTERNAL_WALL	PAVING_EDGE	Sites with no residential lots, such as commercial or industrial sites: along the edge of paving that has grass behind it.
INTERNAL_WALL	BUILDING_EDGE	Sites with no residential lots: along the outer thirds of each face of a building of 2,000 m² (21,500 ft²) or more, on faces that do not touch paving. The middle third of each face is left clear.

On a site with no residential lots, potential grade breaks also run along the earthworks extent, stopping 0.5 m (1.6 ft) back where paving reaches it so vehicle access stays open.

In a Level AI run, potential grade breaks are kept off the road: they sit 0.3 m (1 ft) clear of roads and the earthworks extent edge, and frontage walls stand 0.3 m (1 ft) inside the lot.

When a Level AI run comes back non-viable, its potential grade breaks are loaded into your drawing. Convert the ones you want into grade breaks; a converted grade break keeps its Type and Sub Type, and PAVING_EDGE and BUILDING_EDGE walls convert like any other. You do not need to set Type or Sub Type on a grade break you draw yourself. More information on converting potential grade breaks to grade breaks is found here.