Rural road widening

[mikec1972]

I have to widen an existing tarmac rural road from 6 to 7.5m over a length of 200m. Being rural the road has no existing gullies or piped surface drainage. The drainage for the road is just over the edge into a grass verge with no positive fall or outfall point, the verge is up and down so rainwater must just infiltrate away. If i was to widen the road i would need some form of roadside infiltration the local authority have suggested some form of stone filled trench within the verge to prevent standing water in the verge almost like a french drain but with no pipe in the base as we do not have an outfall point. My only concern is that by providing a stone filled trench adjacent to the road this may affect the sub-base/capping of the road and invite infiltration of the sub grade. We don't have any room for soakaways so does anyone have any ideas or a detail i could adopt? Also in widening the road by 1.5m would you advocate concrete instead of the base and sub/base capping layers or would you go with bituminous full depth construction, if we were to have concrete then would we need any joints as we would be having a 200m by 1.5m concrete strip? Thanks in advance

 

[ACtrafficengr]

The first question has to be what are your soil conditions? If you are on gravel or sand, infiltration methods can work quite well. If you're on silt or clay, they won't work as well if at all.

The second is what is the volume and character of the traffic using the road? You have to design the roads to handle the loads.

I would not widen a tarmac road with concrete. People will think it's a sidewalk. You might be able to build the strip, then overlay the entire width with thin white-topping.

Can you extend your drainage beyond your 200m section to an outfall?

Are you an engineer? If not, you should hire one. This is too big a project for an amateur.