If you have roots which vary in diametre from 5cm to 20cm, and the builder 'accomodates' say, a 8cm root, will the 'accommodation' suffice when it gets to, oooh, say, 27cm?
So, I'll presume what the builder is hoping to be able to do is to create pillars of concrete on to which to rest the lintels; After all, I would think that there would be no point in putting concrete under a root. So, essentially, the wall would be built on a bridge of lintels? Sure would benefit drainage and therefore lessen the pressure on the wall to some extent.
And I'll assume that the idea will be to have, say 4 lintels abreast and in staggered formation: (like as in laying grass turfs) in order to limit the potential of the cracks which would most likely occur if they weren't laid thus.
A lot of trouble, and expense for a 1m high retaining wall. Why not go for a drystone wall? And whilst I think of it, I've seen this done (albeit only around 70cm high) with stkaes driven into the ground, leaning towards the bank of earth and wooden slates nailed inbetween.
Thanks for the comments. I think the wall needs to be a fairly substantial one, because there are buildings about 4 metres away on the high side. The height difference is currently retained by a wooden fence with 4" posts, but it is starting to lean over.
Does anyone have any comments on replacing the existing wooden fence with a fence using 5" concrete posts set in concrete, with concrete gravel boards to retain the soil. I think this is known as a "Berlin Wall" in the building trade. Hopefully it would be possible to position the posts so that they don't interfere with too many roots (there are only 4 trees along the 9 metre fence).
I think I'm going to get an engineer in to advise, but the idea of using concrete fence posts and gravel boards appeals to me initially.