Road Widths & Batter Rails

Página 1

Road Widths & Batter Rails

Introduction When looking at a cross section of a road, if the road surface is lower than the surrounding ground, this is known as a cutting - as you have cut into the ground to lay the road. If the road surface is higher than the surrounding ground, this is known as an embankment - where the ground has had to be built up before laying the road surface on it.

Terms The reduced level (RL) at A and E are the same in both the existing profile and design profile.

In the existing profile, RLa = RLf + Wlg where g is the gradient of the existing ground.

From the design profile, RLa = RLb - (Wl - b/2) x s where s is the gradient of the designed batter.

Therefore, RLf + Wlg = RLb - (Wl - b/2) x s

And so we can rearrange to find Wl.

Cross section - crossfall

If the carriageway was designed as a totally flat surface, we would have a problem with drainage. We therefore apply a crossfall, or superelevation. Standard crossfall is 2.5%.

Superelevation is applied on bends to assist with vehicle control and to avoid adverse cambers. There should be a smooth transition between the differing crossfalls along a stretch of road.

Batter Rails

Batter Rails

To construct an embankment on site, we will need guidance to ensure the correct side slopes are achieved. We can use a batter rail for this. The batter rail defines the line of sight that is parallel to the slope of the embankment we are constructing. A traveller of fixed height can be used on site to check the slope. The leading stake should be positioned at a suitable offset from the bottom of the batter to prevent damage from machinery. The line of sight parallel to the slope is defined by the top of the batter rail.

The same method can be used when forming a cutting.