Vertical Curve-Highway Engineering

Jobghost.blogspot.com explains most important topics in Civil engineering for the GATE-2016 examination. Here the “TRANSPORTATION ENGINEERING-Vertical curves such as summit curve and valley curve” topics are explained. Each and every word given below is important for all your civil engineering competitive examinations. And also the GATE-2016 practice sets, Example problems, previous year Question papers are available in jobghost.blogspot.com.

Vertical Curve

The vertical curves are made whenever the ascending and descending gradients met. And vertical curves should be designed carefully with all provisions of sight distance, headlight distances to provide safe driving zone to the road users. And it should also consider the acceleration of the vehicle moving in the descending gradients.

Based on the gradients meeting each other the curves are classified in to two categories.

1.Summit Curve:- (Sc)

Whenever the descending gradient follows the ascending gradient it is called Summit curve also called as hog curve. This curve is called as summit because the different gradients meets at its summit (i.e. highest point).

Summit curves are provided when:

 i. Negative curves meets Steeper negative curve.

ii.The design is only based on the sight distance of the curve.

a.   Length of summit curve based on SSD

Case-1: If L_s > SSD:-

When the length of curve is assumed to be greater than the required sight distance then the curve length is calculated as below.

Case-2:  If L_s < SSD:-

When the length of curve is assumed to  lesser than the required sight distance then the curve should be designed as below.

b.   Length of summit curve based on OSD

The overtaking sight distance has to be considered while designing the vertical curves. Below are the two conditions to calculate the length of curve based on the required overtaking distance.

Case-1     If L_s > OSD

Here

Ls ---> length of S.C

N----> Grade difference (N₁-N₂=N)

S ----> Sight distance

2.  Valley Curve: (V.C)

When the Descending gradient meets ascending gradients then valley curves are provided. The curves are also called concave or sag curve. Cubic parabola is preferred in the valley curves.

Length of Valley curve calculated based on two criteria 

a.   Length of valley curve based on Headlight sight distance:                             

Case-1     If L_s > SSD

Here

Ls ---> length of V.C

N----> Grade difference [-N₁-(+N₂)=N]

S ----> Sight distance

a.   Length of  valley curve based on comfort of passengers:

Whenever the vehicle moves in the summit curve, the passenger should feel comfortable. It should not offer any jerk or discomfort to the passenger. So the curve should be designed for the gradual change of centrifugal force.

C -----> Centrifugal acceleration (0.6 m/sec³)

N----> Grade difference (N₁-N₂=N)

Impact Factor: 

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