Ditch Depth

Use this function to define and ensure the minimum depth between the roadbed/formation to the ditch bottom in order to prevent surface ditch water from encroaching on the road pavement.

• The minimum ditch depth is to be specified for both the right and left side ditches, as illustrated in the figure shown below.

• The minimum depth value need not be the same for both sides; different values can be defined.

• A = Formation level/Subgrade/Compacted subgrade/Natural subgrade/Roadbed

• B = Ditch depth (minimum ditch depth under the formation level/subgrade/roadbed on both sides)

Run the function from the following location of the floating window Road Model:

MOUS_ICO Menu: Data > Cut and Fill Elements > Ditch Depth

The dialog box Ditch Depth - Minimum Depth below Formation will pop up.

• Use the button Insert to insert a row in the table. Select a row in the table and use the button. The new row will be inserted above the selected row.

• Use the button Delete to delete the selected row.

• Details can be defined on a section basis. The section for the minimum ditch depth requirement is to be defined in the columns From and To.

• The minimum depth is defined in the columns Left side and Right side.

  1. Depth is defined in meters.

  2. Only positive values are to be used.

• Use the shortcut menu of the table.

• Values in the cell can also be copied using the plus symbol (activated when the cursor is at the corner of a cell) and dragging.

• When controls of minimum ditch depth are run (using the button Apply), the road pavement thickness will determine the design of the drainage ditch. For further details, please refer to the figure below.

• The road design standards state that the ditch bottom should be at least 0.350m below the roadbed/formation, calculated below the shoulder edge.

• In the control checks, Novapoint Road Design tests the vertical distance between the lowest surface of the road pavement/roadbed and the outermost point on the ditch surface.

• If the requirement for ditch depth is not fulfilled, the ditch surface will be extended. Note that it is the outermost ditch surface with a negative gradient, which is extended.

• If the outermost ditch surface is defined with a slight gradient downwards in relation to the horizontal plane, the ditch will become inordinately wide.

• If no values are defined in the dialog box, the ditch bottom will be determined on the basis of the surface description defined using any of the following or their combinations:

  1. Simple Road Description

  2. Advanced Road Description

  3. Road Surfaces

Note: As a rule, with a thick road pavement, the ditch gradient must be extended in order to fulfill the depth requirement below the roadbed/formation. Where there is a thin road pavement, the distance from the shoulder edge to the drainage ditch bottom will normally result in determining the depth of the drainage ditch - please refer to the lower part of the illustration.

• A = Horizontal width of ditch surface (foreslope) from surface description (distance between shoulder and bottom of drain)

• B = Ditch depth (minimum ditch depth under the formation level/subgrade/roadbed)

• C = Extended ditch surface (foreslope) considering the ditch depth

• D = Cut slope (back slope) in case ditch depth is not defined

• E = Formation level/Subgrade/Compacted subgrade/Natural subgrade/Roadbed

• F = Terrain surface

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