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Design of vertical alignment
- 1. Design of Vertical Alignment Komal Khetariya 181313140005 Dhavni Pandya 181313140006 Divy Patel 181313140007 Srishti Rana 181313140012 Wyman Chisanga 171310140065 1
- 2. What is Vertical Alignment? The alignment is the route of the road, defined as a series of horizontal tangents and curves. The profile is the vertical aspect of the road, including crest and sag curves, and the straight grade lines connecting them. 2
- 3. Basic components of Vertical Alignment The two basic elements of vertical alignment are Grades and Vertical Curves. Gradient Vertical Curves Gradient: It is the rate of rise or fall along the length of the road with respect to the horizontal. It is expressed as a ratio of 1 in x (1 vertical unit to x horizontal unit). Some times the gradient is also expressed as a percentage i.e. n% (n in 100) 3
- 5. Vertical Curves Vertical Curves are the second of the two important transition elements in geometric design for highways, the first being Horizontal Curves. A vertical curve provides a transition between two sloped roadways, allowing a vehicle to negotiate the elevation rate change at a gradual rate rather than a sharp cut. 5
- 6. Mainly 2 components & Types • Gradient (IRC) Ruling Exceptional Limiting Minimum • Vertical Curves Summit Curves Valley Curves 6
- 7. Categories of Gradients: 1. Ruling or Design Gradient: • Maximum gradient, within that the vertical profile is designed • Difficult to fix because depends on – Type of terrain – The length of the grade ( Change in speed affected by the length) – The design speed (classification of roads) – Pulling power of the Vehicles – Presence of horizontal curve ( provide flatter gradient) 3% for plain, 5% for Rolling, 7 % for Hilly 7
- 8. 2. Limiting Gradient: • Steeper than the ruling gradient • Provide due to topographic constraints • Extra care required – Place a level stretch or easier grade between longer limiting grades – 5% for Plain and Rolling, 7 % for Hilly, 3. Exceptional Gradient: • Provided in extreme difficult situations • Steeper than the limiting • For only shorter stretches ( not > 60 m in one Km) • 7% for Plain and Rolling, 8% for hilly 8
- 9. 4. Minimum Gradient • Provided to drain out the water along the side drains and depends – Surface of the drains ( earthen, R.C.C ….) – Rainfall Run-off – Type of soil – Topography and site condition • 0.2% for used generally • 1% for earthen or open drains 9
- 10. Value of gradient as per IRC 10
- 11. Vertical Curves • Summit / crest curves: Whose convexity upward Vertical curves at a crest or at the top of a hill are called also called summit curves. Crest vertical curves are used to connect two separate inclined sections. • Valley / sag curves: Whose convexity downward. Vertical curves at the bottom of a hill are called sag curves. Sag vertical curves are used to connect two descending grades which form an upside down parabola, or a sag. Similar to crest vertical curves, the sight distance is the primary parameter needed to find the length of the curve. 11
- 12. Shape of Summit Curve 1. Circular Equal Sight distance at all points Most Ideal 2. Parabola Good riding comfort Calculation of ordinates Laying out on ground Most preferred For small deviation angles above shapes doesn’t make substantial difference 12
- 13. Design Parameters for Length • Sight Distance Stopping Sight Distance Overtaking Sight Distance • Centrifugal Force Acts Upwards Counteracted by weight of vehicle 13
- 14. Summit Curve – S < L 14
- 15. Summit Curve = S > L 15
- 16. 16 Length of summit curve(L) for SSD
- 17. Length of summit curve for OSD 17
- 18. Valley curves 18 Valley curves - types
- 19. Length of valley curve for comfort condition: 19
- 20. Length of valley curve for head light sight distance 20
- 21. Design Parameters • Daytime – No Problem • SD reduces at night SSD under head lights • CF acts downwards • W acts downwards • From the above Impact free movement of vehicles Availability of SSD • Transition curves – for safely introducing C.F (P) • Cubic Parabola shape is preferred 21
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