In this topic you will learn how to design horizontal alignment for a highway using ESurvey CADD Road Design module.
In the previous topic you have learnt how to import point data from CSV, Excel and AutoCAD File. Once the ground surface is ready, you can go ahead with Horizontal Alignment design. In Road Design module all the functionalities related to Horizontal Alignment are defined in Horizontal Alignment Tab. You can create multiple alignments with one parent alignment; generally proposed center line of the project will be parent alignment. You can also define super elevation, extra widening. You can also design alignment for strengthening and widening projects. This data stored can be used to prepare the cross sections as the design input.
1. Importing Horizontal tangent lines
Designing horizontal alignment starts with drawing tangent lines in base map.
Open the drawing with base map and draw the tangent lines for the proposed alignment.
Go to ESurvey CADD menu, select Road design-Export Alignment (EXAL) in Road Design submenu in the cad package.
In ESurvey CADD – in “horizontal tab – select import-cad – Import” to see the imported horizontal tangent lines.
In the Alignment name we see that “PCL” is the default name. PCL stands for Project Centre Line. When you import the tangent line by selecting PCL as the alignment – imported tangent lines will be representing the PCL.
2. Adding and editing the names of the alignments
As indicated earlier ESurvey CADD allows you to create multiple alignments in road design projects. This requirement comes when the road is designed considering Left Median Edge (LME) and Right Median Edge (RME) in case of divided carriage way. Or in strengthening and widening projects.
To add multiple alignments, Press the triple dotted button next to alignment name drop down, and add the names of multiple alignments
If required, you can rename the alignment name on this screen
Press New button to add new alignment name. Alignments you added can be at an offset distance from Parent alignment or you can import specific tangent lines to an alignment depending on the requirement
If 5 M median to be provided, we can create LME by giving offset of -2.5 M to Parent alignment and RME can be created by giving 2.5 M Offset to parent alignment.
If we choose to import existing lines to any alignment we can follow the steps as explained earlier.
3. Marking the chainages for the alignment.
It may be noted that chainage can be given only to the parent alignment. You can set any alignment as parent alignment in Alignment name window.
Select the parent chainage in Horizontal alignment tab. Click on Chainage button and ‘Chainage Settings’ window will appear then, specify factors like starting chainage, chainage interval in straight segments and curve segments and enable “Add chainages at station Point” if chainages are required at station points.
4. Design standards Setting
Before we design curves, it is time to set the parameters in design standard window. The design standard settings are given as per IRC. Click on design standard button.
Select various parameters like Transition Curve Type, Terrain, Road Type, Default No of Lanes, Default Pavement Width, Default Normal camber; You can also configure Design Speed and Rate of Change of Super Elevation in this window.
5. Designing the horizontal alignment
You have to select alignment name, which you want to design in the alignment drop down.
You can see that all the apex points of the tangent lines are listed along with deflection angle. You can select all the apex points to fit the curves or depending on deflection angle you can specifically select required apex points individually or in multiples.
Click on Design button to see that all the horizontal curves are designed as per “design standard” settings. If we have added any alignment offset to parent alignment, then that alignment will also get updated.
Note that these curves are designed for “Ruling speed” as displayed in the design standard settings.
In this design process, there may be some HIP points which are not designed. The reasons could be that consecutive curves or their respective super elevations are overlapping or a curve could not be fitted as per design standard settings.
6. Editing the Horizontal Curve
As you have seen in earlier steps, when you click on design software will calculate curve for each apex point and in some cases, it cannot calculate curve as it cannot fit curve as per IRC. The software will allow you to design curves with specific setting and even allows editing of curves designed automatically.
Select the Curve Details sub tab in Horizontal Alignment tab. If the curve is not designed, such points are shown with different color. Click on Edit Curves button to edit.
On the Curve Setting Screen you can individually select each curve and change curve details such as Radius, Transition line length, Super elevation, Widening etc., and update.
You may note that guiding design values are shown in the right side in the curve details group. If you wish to see an abstract of IRC 73 then click on “Reference Table”. You can click on the design button once again to see updated curve details.
7. Viewing the base map or topographical map
In ESurvey CADD you can work with ground points and tangents to design curves. Tangent lines are drawn first in AutoCAD on the base map. Base map will include all the existing features of the corridor.
Now, while you are designing the curve, if you wish to see the base map along with alignment, you have to select “Topo File” option and then select the drawing file having the base map. After selecting the base map, if you refresh the drawing, then you can see Horizontal alignment along with the base map. The same thing can be done when you are working on the Curve Setting window.
In curve setting window you have additional option called Lateral clearance, by giving a Lateral clearance distance on either side of the alignment with respect to selected alignment; you can visualize new alignment along with imaginary lines indicating Lateral clearance. When you see the base map with lateral clearance line you will come to know if there is any interference encountered with respect to any important feature.
In such cases, you can take decision to change the curve parameters.
8. Importing CS data
In ESurvey CADD it is not necessary that you have to have point data for creating the base surface. It can be done with alternate method that is if you have survey data captured from auto level or any other instrument and if you have only offset distance and respective reduced level, then you can import such data which in turn creates the ground surface.
To import Cross Section data – Click on “Import CS Data” Icon, Open the Template and update the excel file and Save it. Select the excel file by clicking on browse button and import the same.
You can generate many reports related to Alignment with details of each curve. Horizontal Curve Calculation Details are available in these reports.
[Show one Report Output]