Broadly the following steps are involved in the upgrading/ widening of Highways

CAD GEOMETRIC DESIGN

GUIDELINES FOR GEOMETRIC DESIGN USING MX SOFTWARE

GUIDELINES FOR CAD GEOMETRIC DESIGN

These guidelines are prepared for the design of Highways using the MX software. The user of this manual is expected to have the knowledge of Highway geometric design, the guidelines of IRC standards and basic knowledge of the menus in MX software.

Broadly the following steps are involved in the geometric design of Highways

1. Surveying the existing ground

2. Downloading data and preparing digital terrain model (DTM)

3. Designing Horizontal alignment

4. Designing Vertical alignment

5. Designing Carriageways & Shoulders

6. Designing Superelevation

7. Designing earthworks

8. Pavement Design & Generating cross sections

9. Computation of quantities

10. Preparation of Plan and Profile drawings

SURVEYING: The surveying is to be done with Total station and GPS. The GPS stations are to be established at regular intervals and the coordinates of Temporary Bench Marks (TBM) are to be taken from the GPS stations. The Total station should have the arrangement of data card to download the survey data into the computer. The points should be taken at regular intervals along the Centreline of the Carriageway in such a way that the digitized surface should resemble the actual ground.

There are mainly three features of survey namely linear features, point features and other features. The linear and point features should be used for digitizing the surface.

The point features are the features taken on the ground and have three coordinates (Northing, Easting and Elevation) and the Point Code. Eg: Trees, Electric Poles, natural ground points, etc.

The linear features are the string of point features joined together and any point on the line can be interpolated to get the elevation at that point. Eg: Carriageway centreline and edges, Embankment top and bottom, building lines, etc.

Other features are the features describe other prominent points. These are only for showing the details in the Plan-Profile drawings, but not used for triangulation. Eg: text, orchard, overhead power lines, top of retaining walls, etc.

Care should be taken while giving the point code. Point code is a four digit alphanumeric character, which indicates type of the feature. The MOSS standard string names are to be used. For this detailed code sheet should be prepared and given to the surveyors before start of the survey. All the point feature codes should start with P.

DOWNLOADING OF SURVEY DATA AND PREPARATION OF DTM: The Survey data should be downloaded into the computer in the form of GENIO format.

1. Import the text file using File> Import> ASCII File. The file type should be GENIO text.

2. This should have a model name of GROUND or SURVEY.

3. Check all the linear features thoroughly like carriageway lines, buildings, water bodies, etc.

4. Edit the survey data using the options Edit strings and Edit Points under Modify. The points can also be edited through MOSS explorer.

5. After editing the features, check with Surface Checker under Analysis for any zero levels, null levels of very high and low elevations. Correct the errors using the Step 4.

6. Analyse the surface for triangulation, contours and level bands. This can be done by using the option Surface Analysis under Analysis.

7. Save the triangulation model with the name Surface Triangles or Ground Triangles.

HORIZONTAL ALIGNMENT DESIGN

Before starting the alignment design, the scheme of widening is to be decided. This differs for two lane and four laning projects. For four laning projects, the side of widening is to be decided based on the availability of land and obligatory points such as religious and important structures, etc. As far as possible, the existing Carriageway is to be used to full extent and fall on any one of the proposed Carriageway. The existing geometric deficiencies are to be rectified subject to the availability of land. The length of horizontal curve should be as large as possible. The existing radii should be retained if it conforms the design speed or else they are to be increased to conform the design speed. If it is not possible to provide the required curve radius for the design speed, the speed is to be restricted locally and suitable speed restriction signs are to be provided at sufficient distance on either side of the curve. The Horizontal Intersection Points (HIP) are to be placed at larger interval as far as possible. Long straight portions with sharp curve are to be avoided. As far as possible, the major bridges should be on the straight portions and should have sufficient sight distance.

1.The Horizontal alignment is to be designed using the option Horizontal Design under Quick Alignment .

2. Create a new model called Design and a string MC00 and press Next>

3. Edit Horizontal appears on the screen. The details are as under:

A F B B H D C C E D G OK

A- set default radius, spiral, etc. E - edit current curve details

B- add IPs, snap to point on or off F reverse alignment direction

C- move IP unconstrained or slide G undo multiple actions

D- insert or delete IP H Construction tool

4. Decide the side of widening based on availability of Right of Way, demolition of structures, etc., add HIPs (B) by using the control points such as the bridges, salient points in the urban areas, etc.

5. Fit the appropriate curve radius and transition lengths for the adopted design speed (use IRC: 38 for selection of curves). For deflection angle less than 1.5o, curves are not required. They can be left as kinks. If the design speed cannot be achieved, the speed is to be reduced locally and proper speed restriction signs should be placed.

6. After finishing the alignment design, click OK to create Master string. Set the chainage interval at which the final cross section drawings are to be plotted.

VERTICAL ALIGNMENT DESIGN

Before starting the Vertical alignment design, the type of construction (overlay, reconstruction or realignment) is to be decided based on the pavement design. For overlay stretches, the bituminous PCC thickness should be kept the minimum or else the material of the PCC should be changed for that stretch. It should be tried to have the same vertical profile for the left and right carriageways. If it is not possible, the difference in levels between the left and right carriageway should be kept the minimum (of the order of 0.3m). The design should be done based on safe stopping sight distance (SSD). For new alignment the subgrade should be atleast 0.3m above the high flood level (HFL) of the area. The distance between the to Vertical Intersection Points (VIP) should be atleast 150m. 0% gradient is to be maintained on all the major bridges. Maximum gradient should be restricted to the gradient specified for the design speed. The vertical curves (parabola) are to be provided if the grade difference of the two consecutive straights is more than 0.5%. Vertical broken back curves separated by short straight should be avoided.

1. The vertical alignment is to be designed using the option Vertical Alignment under Quick Alignment design.

2. Select the Design model and Alignment string.

3. Edit Vertical palette appears on the screen. The details are as under:

A B C D E F G OK

A Set VC parameters

B Delete Profile

C Snap selection

D View details in tabular formE add, insert, move, delete VIP

F Adjust Curve

G Undo previous actions

4. Place the IPs using the add IP button, move the IPs to suit the design and place curves of required length as per IRC: SP 23.

5. After finishing the complete design, select lock start and end button and choose the appropriate options. This is very essential otherwise there may be null levels left in the alignment.

6. To get the guide vertical alignment for the PCC design in overlay stretches, run the MX Renew and get the guide vertical alignment and follow it as close as possible.

DESIGNING CARRIAGEWAYS

Before starting the design of carriageways, all the typical cross sections and the chainage wise applicability is to be decided. All the dimensions like the width of median, the width of carriageway, paved shoulders and earthen shoulders are to be finalised.1. Select the Design carriageways option from Design> Road Design. The following dialogue box appears. Select the appropriate template.

2. Edit the template to suit the requirement and save it in the Project styles folder.

3. Using the above procedure, prepare all the typical templates for the use in the project and save them in the Project folder. If any new project is to be created, copy all these styles in the new project.

4. Prepare the list of chainages and the applicable template for each section.

5. Select each template and give the start and end chainages and click next.

6. The following dialogue box appears. Click next and repeat the above procedure till the templates are attached upto last chainage and finish the operation.

DESIGNING SUPERELEVATION

Superelevation should be provided for the horizontal curves for the specified design speed. The min. rate of change of superelevation should be 1 in 150. If the application length is not sufficient, the design speed is to be reduced locally.

1. Select the Rule based Superelevation option from Design> Road Design. The following dialogue box opens

2. Select the appropriate Alignment string and start & End chainages. Click next button. MX prompts for the relevant Superelevation rules. Select India 4 lane Motorway and design speed as 100Kmph and click next.

3. Select the appropriate pivoting method. For the present case, the first method is to be adopted. The superelevation application type should be Linear. Click next.

4. Select the inner and outer edges of left and right carriageways and select next.

5. After processing and calculating the application lengths and stations, MX returns the conflicts. Review the conflicts and click edit.

6. Edit the application stations and applications lengths if required. Save the Report and check carefully all the curve application stations. It is better to calculate the application stations in Excel and compare with the stations in MX. Then click finish to complete the superelevation calculation.

DESIGNING WIDENING PORTIONS (BUSBAYS) AND SHOULDERS

1. Select the road widening option from Design> Road design> Road widening. Select the alignment string and the carriageway edge to be widened.

2. Give the start chainage, end chainage, taper length in and out and taper width (widening width).

3. Select the shoulder design option from Design> Road design> Shoulder Design. Select the alignment string and the carriageway edge.

4. Select Standard shoulder Method. If any roll over methods are to be adopted, toggle on the Select shoulder Method for curves.

5. Give the shoulder width and the cross fall. Select the start chainage and end chainage. Then shoulder will be created in the drawing. To do it on the right side also, click next and repeat the above steps.

DESIGNING EARTHWORKS

The earthworks consists of the slope of the embankment, the berms if required and the provision of drainage ditches. The slope of the embankment is to be decided based on the geotechnical investigations. Normally 1:2 is to be provided for the embankments of less height. If the height is more than 6m, the slopes may have to be designed and berms are to be provided or earth retaining structures are required. Cut drains may have to be provided in case of cutting. Suitable guard posts or crash barriers are to be proposed if the height of embankment is more than 3m.

1. Open the Earthwork Model details dialogue box from Design> Earthworks wizard. Select the Alignment string, left shoulder edge and right shoulder edge. Select the ground triangles model and triangulation string name. Click next.

2. Select the appropriate cut and fill styles on left side and right side. Prepare these styles and save under Project styles folder. Copy these styles whenever new project is created.

3. The styles can be modified from the existing style sets in MX public style sets or new styles can be created from the dialogue box shown below. The drains, berms, etc are to be included and the slope at which the embankment line touches the existing ground is to be given.

4. Select start chainage, end chainage, strategy of cutting the ground and type of slope signatures. Once finish button is clicked, the cut and fill lines are generated in the plan.

GENERATING CROSS SECTIONS & QUANTITIY CALCULATIONS

Before the start of this, the design of pavement layers is to be completed. The pavement layers and thickness for the main carriageway, paved shoulder, earthen shoulders and the layers to be continued in the median are to be finalised. The cross sections are to be plotted at regular intervals, normally at 50m interval. All the salient points such as the start and end of transition, start and end of circular curves, etc. are also to be plotted. The earthworks and pavement layer areas of all the cross sections are to be computed and the quantities should be computed by end area method.1. Select the cross sections from Analysis> Sections> Cross sections. Select Create cross sections wizard, identify the reference model, alignment string and the ground triangulation model.

2. The cross sections are cut at regular intervals and can be seen on the cross section viewer. View all the cross sections carefully, edit the cross sections using the cross section editor and save the cross sections model as Design Sections.

3. Select Design> Pavement and subgrade design. Select design model and alignment string.

4. Select the Design sections model and existing & Proposed section sets. Select the Pavement Layer Design option from Pavement and Subgrade Design

5. Select the appropriate pavement layer style sets. If there are more than one set, (eg. Left CW, median and Right CW) create all the sets and place as different Zones. If the pavement design is different for different stretches, add them as different areas.

6. Check the cross sections carefully and after displaying all the cross sections, click finish to save the cross sections

7. Select the cross section working drawings option and plot all the cross sections. Save them as Auto CAD file and edit for final printing.

8. Select the Reports and save the reports of earthwork quantities and pavement quantities as Excel file.

9. For earthwork quantities, the area should be between existing and subbase. Check the Pavement layer volumes by calculating in Excel.

PREPARATION OF PLAN & PROFILE DRAWINGS

Before plotting the final drawings, the size of the drawing, the horizontal and vertical scale and the annotations to be provided under the profile are to be finalised. Normally 700m on A3 sheet and 1000m on A2 sheet can be fitted for the Horizontal scale of 1:2000 and vertical scale of 1:200.1. Select Create new drawing option from Draw> Working Drawing. Select Plan and click next.

2. MX prompts for Master alignment. Select Master alignment and click next. Give the details like horizontal scale, length to be fitted in each sheet, overlap length etc, and click next. 3. Edit the start and end chainages according to the requirement and click next. Save the page setup and exit the plan layout.

4. Select Create new drawing option from Draw> Working Drawing. Select Profile and click next. Select the appropriate design alignment and the ground triangulation. Select create drawing option.

5. Select all the options related to annotation details, scale to be plotted, Horizontal and vertical annotation details, superelevation details, etc and select OK. The Profiles are cut at the given intervals. These can be edited in the AutoCAD, pasted in the Plan drawings and the final Plan and Profile drawings are to be inserted in the Title blocks.

6. The drawings are to be enhanced by putting the horizontal curve details, locations of culverts and bridges, sign board locations, etc. The final drawings are to be plotted and checked thoroughly before final submission. QUALITY ASSURANCE PLAN FOR GEOMETRIC DESIGN

Project Name:

Stretch:

Designed by:

Date of receipt of Survey data:

Digital Terrain Model (DTM)

DescriptionPrep. byChk. byDateRemarks

Import Survey data

Check linear/ point features

Place text

Check levels

Surface analysis and triangulation model

Check data at site

Any spl. Instructions given to surveyors

Incorporation of corrections

Design of Horizontal Alignment

Design Speed:

DescriptionPrep. ByChk. ByDateRemarks

Check deficiencies in existing design

Identification of HIP locations

Fit the curves and transitions

Identify the structures affected by the designed alignment

Check the designed alignment at site and correct for final alignment

Design speed check

Incorporation of changes identified in checking

List of locations where design speed could not be achieved

Location ( From To)Radius providedAchieved speedReasons & Remarks

Design of Vertical Alignment

DescriptionPrep. ByChk. ByDateRemarks

Identify Overlay stretches

Identify raising stretches

Obtain the guide vertical alg. from MX Renew

Identify VIP locations

Fit the curve lengths

Provide 0% gradient on major bridges

Finalise the Proposed Road levels at all the culverts/ bridges

Identify location of new culverts

Design speed check

Finalise Overlay and Reconstruction locations

List of locations where design speed could not be achieved

Location ( From To)K factorAchieved speedReasons & Remarks

Design of Superelevation

DescriptionPrep. ByChk. ByDateRemarks

Calculate the application stations in Excel

Check with the stations in MX

Design speed check

List of locations where design speed could not be achieved

Location ( From To)e% providedAchieved speedReasons & Remarks

Miscellaneous Items

DescriptionPrep. ByChk. ByDateRemarks

Design carriageways

Design busbays/ truck laybyes

Embankment & cut lines

Identity the locations of guard posts/ crash barriers

Median opening details

ROW for proposed improvement

Pavement design styles

Plot cross section drawings

Check cross section drawings

Verify PCC and rectify if needed

Computation of quantities

Preparation of Plan/ Profile drawings

Enhancing Plan/ Profile drawings

Placing of culverts and horizontal curve details in plan and profiles

Identification of road sign locations

Identification of Major and minor intersections and design

Utility relocation/ Land acquisition reports

Setting out details of horizontal and vertical alignment

Signature of the Designer

GEOMETRIC DESIGN STANDARDS

Design speed -100 Kmph (desirable)

80 Kmph (Minimum)

Cross sectional Elements:

Element CharacteristicsDesign Values

Width

Carriageway7.25m*

Paved Shoulder1.5m

Gravel shoulder1.5m

Median4.5m

Slow/ parking lane3.5m

Cross fall

Carriageway 2.5%

Paved Shoulder2.5%

Earthen Shoulder3.0%

Median3.0%

Embankment side slope1 : 2

* 3.5m for each lane and 0.25m for kerb shyness

Safe stopping sight distances (SSD)

Design Speed (Kmph)SSD

100180

80130

Horizontal Alignment:

ParticularsDesign Speed (Kmph)

10080

Max. deflection angle without horizontal curve (o)1.01.0

Min. radius of Horizontal curve360230

Formula for superelevationV2/225R

Max. Superelevation (%)77

Min Rate of change of superelevation1 in 1501 in 150

Axis of rotation in superelevated stretchesRotation about median edges

Min. length of transition curve required for different radii

Radius of curveMin. length of transition (m)

100 Kmph80 Kmph65 Kmph

100NA

15080

17070

200NA60

2409050

300NA7540

3601306035

4001155530

500954525

600803520

700703520

8006030NR

9005530

10005030

120040NR

150035

180030

2000NR

Superelevation (e) to be provided for different radii

Radius of curveSuperelevation required (%)

100 Kmph80 Kmph65 Kmph

100NA

1557.0

1707.0

200NA7.0

2407.07.0

300NA7.06.3

3607.07.05.2

4007.07.04.7

5007.05.73.8

6007.04.73.1

7006.34.12.7

8005.63.6NR

9004.93.2

10004.42.8

12003.7NR

15003.0

18002.5

2000NR

Vertical alignment:

ParticularsDesign speed (Kmph)

1008065

Gradient (%)

Ruling3.33.33.3

Max.5.05.05.0

Min.*

Min. K Value (for safe stopping sight distances)

Summit curves743319

Valley curves422618

Grade difference not requiring vertical curve (%)0.50.60.8

Length of curve = K x grade difference

* Flatter gradients can be adopted if the sufficient cross fall is provided

Length of Summit curve for different grade differences

Grade difference (%)Min. length required (m)

100 Kmph80 Kmph65 Kmph

0.560NRNR

0.66050NR

0.8605040

1.0755040

1.51105040

2.01506540

2.51908550

3.022010060

3.526011570

4.030013075

Length of Valley curve for different grade differences

Grade difference (%)Min. length required (m)

100 Kmph80 Kmph65 Kmph

0.560NRNR

0.66050NR

0.8605040

1.0605040

1.5605040

2.0855540

2.51056545

3.01308055

3.51509065

4.017010570

LIST OF CODES TO BE FOLLOWED

Geometric elements

IRC 73: Geometric design standards for rural highways

Horizontal alignmentIRC 38: Guidelines for design of horizontal curves for highways

Vertical Alignment

IRC SP 23: Vertical curves for highways

Junctions

IRC 41

Road signs

IRC 67

Road Marking

IRC

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