Subgrade
Topsoil and Vegetation Removal
Use this function for the following:
Removal of topsoil and vegetation (Sub-surface - Material Type 16 to 20 and 21 to 25) at desired sections.
Termination of slope surfaces.
This function can be activated from the dialog Subgrade and by selecting the tab Topsoil and Vegetation Removal.
Vegetation and topsoil are most often loose materials with little load-bearing capacity. They should be removed during road construction with low embankments and sloping verges.
In all cases, the topsoil layer ought to be scraped away (retained), where the soil could, for example, be used for covering slopes and landscaped surfaces to reclaim agricultural areas.
The vegetation and topsoil layer can be defined in two different ways:
The layers are part of the terrain model, defined in separate groups with level coding.
The layers are part of the road model, while the terrain model only describes the terrain surface.
It is possible to give separate parameters for cut and fill for topsoil removal.
The removal of topsoil and vegetation has a lot in common with the Soft Spot Removal function described below.
Topsoil, vegetation, and fill material will be treated as one item in the profile calculation.
The quantities will be calculated and specified by soil type, but will be treated somewhat differently.
If soil excavation is to be carried out in a section, the excavated soil will be removed to rock or hard ground regardless.
As a rule, topsoil and vegetation will only be removed if demanded by the criteria for terrain gradient and embankment height in accordance with road design standards. However, these can be removed manually.
Refer to the topic Topsoil and Vegetation Removal - Examples.
The dialog box Subgrade with the tab Topsoil and Vegetation Removal:
Insert - Use this button to insert a row in the right pane of the dialog box.
Select a row, above which a new row is to be inserted and click the button.
Delete - Deletes the selected row from the right pane of the dialog box.
When the cursor points to the corner of the cell, plus symbol will pop up, hold the symbol, and drag to copy the contents of the cell.
Section
Define the section, from where the topsoil and vegetation are to be removed using the columns From and To.
Excavation can be formed in different ways, refer to the topic Topsoil and Vegetation Removal - Examples for more details. The shape is determined by comparing three parameters:
Fill
Cut
Criteria - Set criteria for the pull-down menu. Novapoint Road Design will remove the topsoil vegetation when the criteria are met. Available criteria are as follows:
Design standard
Always
As specified
Design Standard
Topsoil and vegetation will be removed if the average terrain gradient between the foot of the fill on the right and left sides, or possibly between the foot of the fill and the top of the cutting, is steeper than 1:6.
Topsoil and vegetation will be removed when the fill height is less than 3.0m. The height will be checked below the left and right shoulder edge and under the centerline. The layers will be removed if one of these heights is less than 3.0m.
Always
Topsoil and vegetation layers are removed regardless of terrain gradient and fill height. The same applies if any underlying layers (soft spot excavation) are removed.
As specified
You can define your own values for fill height criteria and back slope gradients. The average terrain gradient (1:6) is a fixed value and cannot be changed.
Apply
Use this button to execute the function.
Examples
Topsoil and vegetation removal can be done in various ways:
Design 1
Using design 1, an ordinary fill surface will be laid out on the side of the embankment as the lower edge of the vegetation and topsoil layer. From there a surface will be laid out with the soil-cutting slope up to the terrain's top surface. In soil cuttings, the cutting surface will continue, unbroken, up to the top surface. With rock underneath, a break in the transition is formed. Changes from rock cutting to a terminating slope with soil cutting slope.
Design 2
Using design 2, in embankments, the fill surface will be extended down to the lower edge of the vegetation or topsoil layer. From there, a vertical surface will be inserted into the cutting of the terrain's top surface. On the side of the cutting, an equivalent termination surface will be inserted from the bottom edge of the vegetation and/or topsoil layer, and up to the terrain level.
Design 3
Using design 3, in embankments, the fill surface will be extended down to intersect the top terrain layer. From there, a vertical surface will be inserted cutting through to the lower edge of the topsoil or vegetation and rising back to the terrain surface using a normal cut slope. In soil cuttings, design 2 will be applied.
In sections with both topsoil/vegetation and soft spot materials, these layers will be treated as one in cross-section calculations. Not all combinations are permissible, formats 1 and 2 can be freely combined, but design 3 will be applied to all layers in the same cross-section.
In cross-section calculations, Novapoint Road Design will first check whether the criteria demand the removal of topsoil and/or vegetation. In that case, the fill slope and rock/soil cutting would be laid out, at the outset, as the lower edge of the vegetation and topsoil layer. The selected format will therefore determine how the termination surfaces will be shaped. Mandatory removal will mean excavation in any case. Termination surfaces will be saved with the surface number being used internally by the road model.
Soft Spot Removal
Use this function to remove loose soil, peat, fine soils with high humus content, wet clay, etc., to consider the soil bearing capacity underneath the road construction.
This dialog can be activated from the function Subgrade and by selecting the tab Soft Spot Removal.
Loose fill with poor load-bearing characteristics underneath road constructions should, in individual cases, be replaced by for example rock fill.
Soil excavation should be carried out where the ground consists of peat, fine soils with a high humus content, or wet clay.
The soil is excavated down to rock or firm ground (earth base codes 1-5).
To remove/excavate these kinds of soil, details are to be defined in this dialog box. No automatic methods have been included.
These types of soils can be defined in two different ways:
The layers are part of the terrain model, defined in separate groups with level coding.
The layers are part of the road model, while the terrain model only describes the terrain surface.
Depending on the complexity of a given project, the user can select between two different methods – simple or advanced.
Simple Method
Advanced Method
A method is selected using the respective buttons on the dialog box Subgrade.
If a method is in use and you wish to switch to the other method, delete all existing input data for the present method before switching to the other.
The removal of topsoil and vegetation has a lot in common with soft spot removal.
Refer to the topic Soft Spot Removal - Examples.
Simple Method
This dialog can be activated from the dialog Subgrade and by selecting the tab Simple Method.
Refer to the topic Soft Spot Removal - Examples.
Insert: Use this button to insert a row in the right pane of the dialog box.
Select a row, above which a new row is to be inserted and click the button.
Delete: Deletes the selected row from the right pane of the dialog box.
When the cursor points to the corner of the cell, plus symbol will pop up, hold the symbol, and drag to copy the contents of the cell.
Section
Define the section, from where the soft spots are to be removed using the columns From and To.
Limit and Form
Soft spot removal, using a simple method, is defined by selecting the limit and form of the excavation slope for each section. Select a limit and form of the excavation slope from the pull-down menu of the cell:
Extension of fill slope and normal cut slope.
Extension of fill slope and vertical cut slope.
Vertical fill slope and vertical cut slope.
The principles applied are the same as for Topsoil and Vegetation Removal.
Apply
Use this button to execute the function.
Advanced Method
This dialog can be activated from the dialog Subgrade and by selecting the tab Advanced Method.
Refer to the topic Soft Spot Removal - Examples.
The strong point of this method is its ability to perform soft spot removal independently of fill slope gradients.
This is especially a key factor when fill slopes are designed with little steepness for run-off facilities or landscaping purposes.
In such cases, using the simple method will involve extensive excavation of soft spot material beyond what is necessary for road construction.
Insert - Use this button to insert a row in the right pane of the dialog box.
Select a row, above which a new row is to be inserted and click the button.
Delete - Deletes the selected row from the right pane of the dialog box.
When the cursor points to the corner of the cell, plus symbol will pop up, hold the symbol, and drag to copy the contents of the cell.
Section
Define the section, from where the soft spots are to be removed using the columns From and To.
Depth
Specify the depth (positive values, meter) of soft spot excavation.
The value refers to the elevation of the centerline on the terrain (not the road surface).
Soft spot removal to solid ground (earth and/or rock) can also be specified by defining any character other than a numeric value (in such case, the cell value changes to Complete).
If solid ground rises up through the defined level for soft spot excavation, this is taken into consideration when calculating quantities.
Ray
Define the side gradient of the soft spot excavation "trapeze".
The gradient is to be defined as a ratio with a negative prefix, e.g. a value of –0.5 will give a resulting slope gradient of 1:2 applying for both sides of the "trapeze".
The ray is only used for quantity calculations and will not show on the cross-section profiles.
Cut
Define the gradient of the excavation back slope.
The gradient is to be defined as a ratio with a negative prefix, e.g., a value of –0.5 will give a resulting slope gradient of 1:2 applying to both sides.
Left/Right side - Start point
Define the starting point of the ray on the left side of the "trapeze".
Select a road surface from the pull-down menu.
The outermost point of the surface from the centerline will be the start point.
Correction can be applied indicating an offset from the selected start point.
Left side - Correction
Define an offset (meter) from the selected start point.
Use a sign (+/-).
Positive value results in a displacement to the left.
Right side - Correction
Define an offset (meter) from the selected start point.
Use a sign (+/-).
Positive value results in a displacement to the right.
Apply
Use this button to execute the function.
Examples
Soft spot removal, a simple method, can be applied in various ways:
Design 1
Using design 1 in a fill section, the embankment surface will be extended to the bottom edge of the excavation layer. From there, a soil-cutting surface will be laid out up to the top of the surface. The surface will be defined with the same gradient as the soil cutting (surface group 6) in the surface description. On the side of the cutting, the end surface in the excavation layer will have the same gradient as the soil cutting is described as having in the surface description (surface group 6).
Design 2
Using design 2, the fill slope and the soil or rock cutting will be laid out as the bottom edge of the excavation layer. From there, a vertical termination surface will be inserted into the cutting on the top surface.
Design 3
Using design 3, in a fill-section, the embankment surface will be extended to the terrain surface and use a vertical cut through the excavation layer. In soil cuttings, design 2 will be applied.
Soft Spot Removal has much in common with Topsoil and Vegetation Removal. In sections with both topsoil/vegetation and soft spot materials, these layers will be treated as one in cross-section calculations. Not all combinations are permissible, formats 1 and 2 can be freely combined, but design 3 will be applied to all layers in the same cross-section.
When excavated soil is removed, fill surfaces and cutting surfaces will initially be laid out to the bottom edge of the excavated layer. The selected shape will determine how the termination surfaces should be inserted and their gradient. The termination surfaces will be saved with the surface numbers for use internally in the software.
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