Lintel material type for underground use

Hi all,

I have a small stream crossing at a right angle underneath my driveway. The original conduit was a two foot diameter concrete pipe which has crumbled at one side of the driveway. I don't have the money to hire a digger and do the job properly.

After excavating as much as I can to the side of the driveway there is a still some reduction in water flow which is only a problem during exceptionally heavy rain.

The problem which I hope I can resolve cheaply is that the driveway has lost about six inches in width over about two feet of its length. I envisage doing this by setting lintels into the ground and covering them over with gravel.

They would be above the stream but still in a damp environment so I'd appreciate advice on the choice of material. I'm considering reinforced concrete lintels, RSJs or railway sleepers but these might be subject to erosion, rusting or rotting.

Would any of these work in the long term or is there a more suitable alternative?

Steel beams, ralway sleepers, old iron bed ends etc are ok, just set them up off the bearing area and with formwork to give them a min of 100mm concrete cover all over. Poker the concrete in to get rid of voids. Steel so encased will likely see all of us out.

That was a quick reply

I'd have no problem covering the beams with 100mm concrete but some of their lower surface would be directly above the stream so would that leave them at any significant risk?

Not if they're encased on all sides, including underneath

Or just use some precast lintels, put a blob of concrete over the ends, to potect the wires that you will see.

Thanks.

The work has to be done from above as there's very limited access to the side ( a 2.5' x 2' hole two feet deep) and any failed attempts would result in materials falling into and potentially blocking the stream.

Precast lintels would be the easiest then. I was just concerned that the concrete used in them, being intended for internal use, would probably not contain any waterproofing additive and therefore be subject to erosion.

Nah, the only thing you've got to watch is the exposure of the tendons at either end. The concrete will be fine. Even in Wales....

Sounds like a plan then. Thanks again!