Very shallow foul water pipe - Backfill or encase in concrete?

[MikeJones]

We are looking to add a wc to a outbuilding and utilise a macerator to pump the waste to a new soil stack. This new internal stack is to be connected to a man hole some 13 metres away in our drive on the side of the house. Unfortunately, this man hole is so shallow, that once we have completed the pipework on a 1:80 run (Osma plastic 110mm), the pipe will be approx. 125mm below the surface at its highest point.

Would the pipework be sufficiently protected if we :

1. encased pipework entirely in concrete or
2. filled trench to just above the pipework with pea shingle and then lay 120mm of concrete on top to level

(The drive is made up of 120-150mm concrete on a clay/hardcore surface and on rare occassions a car may be on this part of the drive temporarily.)

Any suggestions most appreciated.

[Tony McC]

My preference would be to encase the lot in concrete, but it all depends on what surfacing/paving you have on the driveway. Obviously, if you have, or plan to have, block paving, bringing concrete up to the surface level is not the best idea.

[MikeJones]

Thanks for the advice.

By the way, excellent website.