Geometric Control of Roads and Tunnels with Point Measurements

Introduction

Geometric control against road and tunnel layers is essentially a Surface control. For road projects, we can also run Line control in the same operation.

Surface Control

In this control, we compare a measured point against a surface in the road or tunnel project. Since road and tunnel projects contain many theoretical layers, we must specify which layer in the SFI model we want to check against.

In SFI models, all cross sections with built theoretical layers are stored. The program uses these to calculate the theoretical point we will compare with. It is obvious that measured points rarely land exactly on a cross section. The program must therefore interpolate theoretical values between the cross sections. This method also takes into account horizontal and vertical curvature.

Surface control can be performed Vertically or Normal to the surface. Both options are active for road projects. In road projects, we use vertical to check asphalt, for example, while we use normal to check cuts and fills.

Figure: A = Normal to, B = Vertical

In tunnel projects, only the Normal to option is active.

In traditional road projects, it has been common to only consider slopes across the road, as the gradient in the longitudinal direction has no significance for the result. However, this limits the use to roads. If we want to take into account the slope in the longitudinal direction, we must generate tilted cross sections. The geometric control will then automatically take into account slope in the longitudinal direction. The option to generate tilted cross sections can be found under the setup for cross section generation.

Theoretical layers in road and tunnel projects consist of many surfaces. We often need to extend specific surfaces. We solve these situations by using Surface selection and Extend last surface by.

Figure: A = Distance

The program contains several examples of surface selections, but we can also enter our own selections as needed.

Example of Surface Selection

We want to check the top of the sidewalk. Some control points may end up slightly outside the theoretical surface. If we only specify one surface in the selection, this surface is extended in both directions.

Surface selection: (-3.01)

Extend last surface by: 1 meter

If we specify a surface selection with a gap in the middle, for example (-3.01),(3.01), the surfaces are extended equally from each side until they intersect (provided that the value in extend last surface is given large enough).

Example of Shoulder Edge Control

We want to check the shoulder edge even if the measurements end up slightly outside, for example on the fill. The shoulder edge should therefore be the outermost active surface on each side of the road.

Surface selection: (-2.01:2.01)

Extend last surface by: 1 meter

We can also check against a calculated layer by entering a Vertical offset or Parallel to layer. The former applies to layers in road projects, while the latter applies to layers in tunnel projects.

Example of Vertical Offset

In road projects, we can create an imagined layer with an offset in relation to another existing layer in the SFI model as shown in the figure below.

Vertical offset example showing the relationship between layers

We specify the tolerance requirement ourselves, from Min. tolerance to Max. tolerance. In road projects, we get a negative value below the surface and a positive value above the surface. In tunnel projects, the rule is different; we get a positive value outside the surface and a negative value inside.

Line Control

We use line control, for example, to check asphalt edges in road projects. This option is not active for tunnel projects.

It is the nearest line that is checked against. You can also choose to check against a specific line by specifying only the corresponding surface in the surface selection, for example (-1.01). If we specify a surface in the selection, it is the line that goes through the end point of this surface that applies. Note that surfaces on the left side (with minus sign) must be specified with parentheses in the surface selection. This is not strictly necessary for surfaces on the right side (without minus sign), but a good rule might be to include parentheses regardless.

Example of Line Control

The example shows the road surface in cross section editing. Surface (-2.01) is marked and the end point is shown with a small cross.

We specify the tolerance requirement ourselves, from Min. side tolerance to Max. side tolerance. Negative values refer to the left side - and positive values refer to the right side of the line.

Default is "Min. side tolerance" -100 and "Max. side tolerance" 100, i.e., points that are within -/+ 0.1 m from the line are within tolerance.

Examples of tolerance values:

• Right side: "Min. side tolerance" 50 and "Max. side tolerance" 100, i.e., points that are within the range 0.05-0.1 m on the right side are within tolerance.

• Left side: "Min. side tolerance" -100 and "Max. side tolerance" -50, i.e., points that are within the range 0.1-0.05 m on the left side are within tolerance.

• Impossible case: "Min. side tolerance" 100 and "Max. side tolerance" -100, i.e., points that are further to the right than 0.1 m to the right of the line and at the same time are further to the left than 0.1 to the left of the line are within tolerance, which is impossible.

Negative value to the left of the line and positive value to the right of the line.

When performing geometric control of roads, we usually measure 3 points in each profile, one point approximately in the center of the road and one point on each side. At the edge of the surface, it gets rolled down somewhat, which gives a deviation that is not representative of the geometric quality that the road otherwise has. Therefore, we normally move the measuring point somewhat inward, typically 0.25 m. We can take this into account by entering a value for Parallel displacement. A negative value gives a parallel on the inside (towards the center line).

Height and line control can be run separately or simultaneously. Which points the program perceives as line control points is governed by corridor width. Points that are outside are not included.

Figure: A = Corridor width

Control Results

Horizontal List Field

After the control is performed, the program outputs the result of the calculation in the layer with measured control points.

Result of calculation in horizontal list field

The following properties are created in the horizontal list field:

• DIFF_ERROR - the vector deviation when checking normal to
• LINE_ERROR - the deviation in line control
• CONTROL_RESULT - the control result of the point. Points that exceed tolerance requirements get an X for too large surface error and an L for too large side error. If you run surface and line control simultaneously, you can get too large error in both, i.e., XL in the column
• CHAINAGE - the profile number of the point
• TEO_DIST_CL - the distance of the theoretical point from the center line
• TEO_HEIGHT_CL - the height of the theoretical point from the center line
• DIST_CL - the distance of the measured point from the center line
• HEIGHT_CL - the height of the measured point from the center line
• D_EAST - the East component of the vector deviation
• D_NORTH - the North component of the vector deviation
• D_HEIGHT - the Height component of the vector deviation

Report

We get a dedicated Excel report for each control.

Example of Excel report for geometric control

Note that we get an extra column, Slope, in the report if the cross sections are tilted.

The figures below provide an explanation of the values in the columns for Measured from CL. The same applies to Theoretical from CL.

Tunnel

Explanation of the values in the columns for Measured from CL. A = Measured point

Road

Explanation of the values in the columns for Measured from CL**

We use a built-in Excel function STDEV() for calculating the standard deviation. Further documentation can be found on Microsoft's website.