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Water and sewer design: Parametric ditch description and mass calculation

When the pipes are finished designed with the exact method, you can continue with automatic building of ditches and calculation of masses/quantities.

Note

Manholes and pipes, for example surveyed as-built data, in application layer can also be used as basis for calculation of ditches. You have a separate function that transfers points and lines with predefined attributes to line definition data. Ditch description and mass calculation described in this section will therefore also apply to the section Documentation of quantities in ditches.

Parametric ditch description

You use the SFI model to design among other things roads, tunnels and ditches. Similar to roads and tunnels, ditches also have their own tab in the SFI model with parameters to describe a ditch.

You can enter parameters that determine minimum distances, among other things:

  1. Slope of ditch wall
  2. Distance from pipe to left wall
  3. Distance from pipe to right wall
  4. Distance from uppermost pipe to backfill
  5. Foundation thickness

The figure shows these minimum distances that define the outer contour of the ditch

All parameters that determine the ditch design are described in more detail in the dialog help for ditches.

Mass calculation

You calculate the quantities by retrieving standard or custom-defined mass types for the ditch category.

Standard mass types are defined according to NS3420 and Process code.

You can find these under the Mass types tab.

Regarding mass types, these are the same whether you design water and sewer systems or document as-built water and sewer systems.

Mass types are therefore described in more detail in the chapter Documentation of quantities in ditches under the subchapter Mass types for ditches.

Figure: A = Road/terrain subgrade bottom, B = Rock

Calculation against subgrade

If the ditch lies in a designed road, you usually want the ditch to stop against the subgrade for the calculation to be correct.

Figure: A = Subgrade

The ditch should be built against the subgrade and not against the original terrain. You can solve this in two ways:

  1. Calculate against adjusted terrain
  2. Clip against advanced section

Calculate against adjusted terrain

For this you can use the Calculate from adjusted terrain function when you generate cross-sections.

This requires that you have inserted a road body with layers for subgrade and that Perform intervention is active for the drawing under Drawing settings....

The layers (for example soil and rock) are then adjusted down to the subgrade. Where the layers lie below the subgrade, nothing happens.

Figure: A = Adjusted terrain (subgrade)

Clip against advanced section

For this you can use the Include 3D objects function (advanced section).

This requires that you have an application layer with a triangular model for subgrade or have inserted a road body with layers for subgrade and that Perform intervention is active in the drawing (choice in Drawing settings).

Figure: A = Subgrade