Project 1 - Geometric Design Parameter- Prerequisites
The following are the elements which are mainly required for Road geometric design.
1.Topography:
The important factor that affects the geometric design is the topography. For a plain terrain, it is very easy to construct the highway as per the standards. As the terrain and the gradient increases the construction cost will increase for a specific design speed. So, to keep the construction cost and time under control, the geometric standards vary with different terrain or topography. This is hence classified as steeper gradients and sharper curves.
2.Selection Of Type Road:
After the topography fix the type road to be constructed based on the usage of road.wheather which type of road is to constructed like Expressway,NHR,MDR,ODR,VR...And design the road as per the IRC
3.Type Of Gradient:
Based on the type of terrain provide the similar gradient and all the cross sectional elements.
4.Horizontal Alignment:
For,Desgining of a Horizontal curve based with the help of IRC 38
R = V^2/127(e+f)
From the IRC 38 Table no 2 the design speeds are to considered.the checks for the speeds also to be done from the table only.
Calculation Of Stopping Sight Distance.
SSD = Vt + ((V^2)/2gf)
SSD = vt + v^2/2g(f+(n)) ( n=gradient)
Calculation Of Head light Sight Distance.
HSD = SSD
Calculation Of Intermediate Sight Distance.
ISD = 2*SSD
Calculation Of Overtaking Sight Distance.
OSD = d1+d2+d3
where as
d1 = Vb x t
d2 = Vb x T+ 2S (T = sq.rt (4S/a))
d3 = V x T
From the IRC 38 Table no 4 the superelevation are considered.
e = V^2/225R
emax = 0.07 as per IRC 38.
Check for the Extra widening if any required as per IRC 38 Table no.7
1.If R is 50<R<300 Provide then widening on both the edges.
2.If R is R>300 Provide then widening on the inner edge.
3.If R is R<50 Provide then widening on the outer edge.
5.Vertical Alignment:
For,Desgining of a vertical curve based on standards is done with the help of IRC SP 23.
These are mostly done for the steep terrains.
1.Summit Curve:
2.Sag/Valley Curve:
As per IRC SP 23 the Summit curve and Valley Curve are Calucuted from the Table No 6.