Sight Distance at Existing Junction

This post is an update to a previous one on the same topic, this one is hopefully more complete.


We have an existing junction and we need to improve the sight distance.

You can use a number of methods to check whether you are getting the required sight distance along your sightline.


1. You can create a profile along the sightline and check the sightline against the existing ground surface and see where the obstruction occurs:

or 2. use the visibility tool 'Point to Point' to check.

These methods only provide an answer along a single line. We can see in profile the depth of the earthworks that needs to be excavated. It would be useful to be able to show the extent of the obstructed view area in plan and get an idea of the extent of earthworks that would be required to provide visibility. To do this we can use a combination of dummy corridors and surfaces to give us the desired result.

First create a profile along your sightline in plan sampling the existing ground surface. Next create a profile from your eye (height 1.05m) to your target (height 0.26m) - see screen grab below.

Next create an assembly using the LinkOffsetandSlope on the Generic tab of the tool palettes.

Create the assembly wide enough to cover the area of interest:

Create a corridor from your sightline alignment, sightline profile and the above assembly. Create a surface from the corridor using top links.

Next create a volume surface using the Existing ground as the base surface and the corridor surface as the comparison. Set the surface style to 2D Solid Level Banding or similar.

In the surface properties for the volume surface set the analsyis to Elevations, create one range and set the max value for the range to zero.

The result will highlight in plan the area where the drivers view is obstructed by the existing ground surface.

Found this useful? Need to learn more? Check out our Advanced Junction Design course HERE

Surface Triangulation max angle problem

One new feature added to surfaces for 2013 is the ability to specify a maximum angle between surface triangle lines. This is supposed to build surfaces more intelligently by removing triangles that exceed the maximum angle and result in less erroneous triangulation.


See the following link for more info:


http://beingcivil.typepad.com/my_weblog/2012/04/autocad-civil-3d-2013-new-features-check-tin-for-max-angle.html


This is intended to be applied to triangles that make up the outer boundary of your surface only. However, after creating a surface (style - Border Only) from some LiDAR data last week I noticed there were 'holes' in the surface. See below:

After some searching I checked the max angle and set this to 'No' and rebuilt the surface and the holes disappeared.

So it would appear that the setting is applied to internal triangles also. (which it shouldn't be according to the help menu)

Stage Storage

I have to thank the guys from Autodesk who showed this a few weeks back at the Autodesk Industry Academy in Amsterdam....

I used to think that this tool was related to the Hydraflow Storm Sewers application and therefore not relevant to this part of the world due to differing hydrologic design methodologies.

However this is a stand alone tool that is a really simple and effective way of calculating the volume of a pond. You can calculate from either a surface or polylines.

Run the command and you are presented with the following dialog box:

In here you can click on Define to add data to use in the calculation - you can choose either surfaces or polylines. I have had a number of crashes when using surfaces but am unsure of whether this is an issue with the command or my surface. The alternative is to extract contours from your surface first and then use these polylines in the stage storage command instead. You can also export a .txt report of the analysis or insert a table of the results into the drawing using the buttons at the bottom of the dialog.

Wind Farm Access Roads - Hardstand Area Design

The following post forms part of an article written for this month's edition of AUGI World magazine on using Civil 3D for designing wind farm infrastructure, pg 54.

http://issuu.com/augi/docs/aw201205hr?mode=window&viewMode=doublePage


It follows on from a previous post on designing the access roads:
http://civilintentions.blogspot.com/2012/03/windfarm-access-roads-earthworks.html
Hardstand Area Design:

Hardstand areas are constructed to provide sufficient space for the cranes to operate during erection of the wind turbines. The hardstand areas must be large enough for the cranes to operate in and also provide storage space for materials.

The hardstand areas are effectively a widened region on the corridor. Typically the hardstand areas are flat and widen at right angles to the corridor, see image below. This can cause problems when targeting the hardstand widen alignments using an assembly on the centreline alignment. Civil 3D targets perpendicularly from the baseline alignment and will not model the hardstands correctly at the widen region.

There are a number of methods for modelling this type of widening.

a)  You could add offsets to your assembly and use the offset alignment to provide the offset value. This method gives mixed results when the widening is perpendicular to the main alignment.

b)  You could also create a featureline defining the edge of the hardstand and then use the grading tools to model the earthworks – this has the advantage of correctly modelling the grading in tight corners where the corridor would otherwise overlap. The disadvantage is that you have a number of ‘parts’ to your model and increased margin for error.

c)  The third method involves adding the hardstand alignments as new baselines to the corridor and applying earthworks assemblies along these baselines. This results in one object (the corridor) controlling the earthworks thus reducing the amount of ‘parts’ in your model. This is the method that has given the best results and the one we are going to look at here.

Step1: Create Hardstand Alignments and Profiles:

Create alignments defining the left and right edge of the hardstand and then create profiles along these alignments. As mentioned above, the hardstand areas need to be flat - the profiles along the edge of the hardstands need to be at the same level as the centreline profile. To achieve this we will use a dummy corridor to provide levels along the hardstand alignments.

To create the dummy corridor first create an assembly that has 0% grade and wide enough to extend beyond the extents of the hardstand. The LinkOffsetandSlope generic subassembly works well, see below.

Next build a dummy corridor along the centreline using the assembly. See below.

Create a surface from the corridor and finally a surface profile along each of the hardstand alignments sampling the dummy corridor surface. This gives our levels along the edge of the hardstands.

Step 2: Create Hardstand Assemblies:

The hardstand assemblies will be applied along the left and right hardstand alignments. The left and right assemblies will consist of the left and right earthworks subassemblies used in the main access road assembly.

Create your new assembly. Select the earthworks subassemblies from the main access road assembly. In the case below I am selecting the ditch, conditional cut/fill and generic subassemblies used to model the earthworks for the left side of the road.

Copy these to your hardstand assembly and repeat for the right hand side. Your finished assemblies will look something like the following:

Step 3: Add Baselines and Set Corridor Properties:

Next add the hardstand alignments to the main corridor as new base lines. In the corridor properties add a region to each of the new baselines for the chainages of the hardstand.

Anyone who has used corridors to model earthworks in tight corners will know that the downside is that the corridors do not resolve the overlap on the insides of bends similar to the grading tools– see screen grab below.

To resolve this issue we can use a workaround. In the corridor frequency for the hardstand regions set the sampling frequency to a value greater than the total length of the alignment and set the additional sampling frequencies to ’No’.

This will result in no automatic corridor sampling frequencies being applied to the region. We will then add in sampling stations manually at points along the region ensuring there is no corridor overlap in the earthworks.

This will not result in a perfectly modelled corridor but the differences in terms of volumes calculations are tiny in the grand scheme of things. The benefits achieved by having one corridor where you can easily make edits and create surfaces for volume calculations far outweighs those of having a 100% perfect model.

Wind Farm Design - Creating Geological Surfaces from Probed Depth Values

This post forms part of an article written for this month's edition of AUGI World magazine on how to use Civil 3D for designing wind farm infrastructure, pg 54.

http://issuu.com/augi/docs/aw201205hr?mode=window&viewMode=doublePage

Creating Geological Surfaces from Probed Depth Values:

Probed depths or borehole logs provide us with information on the subsurface geological layers for the site. When importing and using this data in Civil 3D there are a couple of issues that need to be looked at.

Issue 1: The surfaces created from the depth values in Civil 3D are of limited use. What we really need are the elevation values at each of the probe locations.  We need to convert the depth values into elevations.

Issue 2: Due to differing surface data resolutions (typically more points in the existing ground surface) the bottom of peat surface may not appear to accurately represent the geological layer – it may not ‘follow’ the lie of the land. See screen grab below. (You could in some cases see your subsurface extend above the existing ground in section). We need to create a surface that uses the probed depths and also ‘follows’ the existing ground in the areas in between where we do not have any probes.

There is workaround that has previously been posted on a number of blogs and forums that solves both of these issues. Here it is described as applied to a windfarm project - with a little bit of explanation of what is going on in the background from a Civil 3D point of view.

Solution:

1. Create a TIN surface from your probed peat depths – call it Probed Peat Depth.
2. Create a volume surface using the Existing Ground surface and the Probed Peat Depth surface – call it Peat Volume. The order in which you add the surfaces is important (base – Probed Peat Depths, Comparison – Existing Ground). You now have a volume surface that has depth values that are equal to the elevation for the bottom of peat.
3. Create a new TIN surface and call it Surface from Peat Volume. Paste in the Peat Volume surface. Pasting a volume surface into a TIN surface creates a surface with elevations equal to the depth values of the volume surface– we now have a TIN surface representing the bottom of peat.

The surface created in step 3 uses the probed peat depth values and follows the existing ground in between probes.  Note – this is not a true representation of the sub-surface geology but it is a good base to start with.

Compare Drawings

The compare sheets tool in Autodesk Design Review is a great tool for checking for changes in geometry between different issues of a drawing. The tool only works on DWF files however. In my experience most people issue drawings in PDF format which meant the tool couldn't be used.


There is a workaround however. You can convert PDF's to DWF's using the DWF writer printer driver which you can download from the following link:


http://usa.autodesk.com/dwf-writer/


This will allow you to print to DWF from a number of document formats including PDF. Below is the print dialog box from Adobe Reader.

Surface Analysis Precision

This bugged me a while back and I meant to post about it.


I created a volume surface to show extent of cut/fill along my access road - red for cut and green for fill. I used the 2D Solid Level Banding surface style from the AutoCAD Civil 3D 2013 UKIE drawing template. I set my no. of ranges in the surface analysis to 2 which picks up the min and max levels on the surface and divides the level difference into two ranges.

All going well so far until I click ok and look at my surface... which appears to have 'holes' in it.

So why was this happening if I set it to automatically divide the surface into two ranges? The answer is in the surface style settings. The range precision is set to 1 which meant the max elevation for range 2 in my surface analysis stopped at 1m when in fact it was greater than that.

Setting the precision value to 0.001 and rerun the analysis solves the problem. Max elevation for range 2 now corrected to 1.293m.

The holes in my surface are no more...

The surface elevation analysis appears to begin at the absolute lowest elevation (ignoring precision) and work up to the max value (precision applied) - whereas I had always assumed that it found the absolute min and max levels first and then divided the difference into the specified number of ranges.