From the Ground Up

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posted 08/20/08 by Jack Strongitharm Widening Part 2

So where we left part 1, I created a surface to look at what I had done and all was not well.
Why, could be a couple of reasons, the survey was not clean, the road was that deformed along the original crown and left channel that meant it was not going to be suitable.
So we need to revisit and do a little more design work. Also the local authority has a bit more money to spend, so we can actually resurface the whole area as it will improve the friction of the road for braking purposes and generally improve the drainage.



So rather than the crown just being a 3d polyline, convert to 2D line and generate an alignment from it.
Looking at the profile, we then redesign and create a smoother vertical profile.



If we draw the profile along the ‘Widening Alignment’ and display the surface profile we got from the extended surface projection, you can see where some of the problems came from.



So what we can do here is say we will want the new road cross section to be -2.5% (1:40) from the crown line to the widening. We could simply just apply this in the assembly, but we have to tie in the start and end profiles.
Therefore the method I always use is that of creating a temporary corridor or what could be called surface projection to help me design the profile on the widening alignment.
So create an assembly that has the -2.5%, but make the width much bigger so that it will be overlapping the widening alignment in plan.



The reason for this is that we can then make a corridor surface and cut a profile from it.



So the thick pinky red line is showing surface levels at -2.5%



Design through a vertical profile based on this line and tie into the original ground at both ends



To then overlay the original road surface and then have new construction to the widening area we need to have an assembly such as this one.



From the crown line I have placed the generic pavement assembly, found in the Metric/Imperial Roadway or Carriageway (depending on your language version)



Why?, well we can specify our own codes and also all I want is to show 100mm thickness and anything below that will be regulating base course or planing. So give a top link code of overlay and bottom link code of Formation. For linework an outside top point of EC, ETW etc



For targets, the left channel for width purposes of the overlay and the widening alignment for the new construction. Also target the widening alignment profile for level.
For the opposite side just use the 3dpolyline for the channel edge to tie into existing. (you may want to join your channel lines together if you have a gap)



So here is the result (you may want to add that link code style for Overlay to your code set style so to colour it in etc)



And also if you create a surface to the corridor you can see that the contours and slope arrows look good.
As we only called the generic subassembly link code overlay, you can add both TOP and OVERLAY to create the top surface.






Next, we can look at volumes, for this we need a formation or datum surface to the underside of the paved surfaces to measure, regulating and planing for the overlay and also earthworks for the formation of the new widened section.



So create two surfaces in the corridor and name accordingly and add the link code for the formation/datum.



From the prospector and create surfaces, then create tin volume surfaces from the ground to these surfaces.



Using the 2D solid level banding style we can go to the volume surface properties and analysis tab.
Add two ranges, and set as below where you have the biggest cut to 0 as red and from 0 to the biggest fill as green for instance. Set for both tin volume surfaces



So here you can see there is quite a bit of cut and planing to be achieved.



So we can now add some surface tables to reflect the data, so from the surface menu and tables add two tables for each tin volume surface.
Make a copy of the table style, because then you can add you own table title and extra columns, in this case surface area and volume





Don’t forget everything here is dynamic, so now you can spend some extra time on the design of the crown line and maybe optimise the earthworks and overlay regulating and planing.
The only thing you will have to do is reset the limits of the analysis to the tin volume surfaces.
Another easy addition!
Until next time, will there be a part 3?

Jack Strongitharm

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