Joined: July 2004
||Posted: 06 Mar. 2019,12:30
To install a new sewer beneath an existing slab is a bit of a task, and possibly not one best suited to a DIYer.
The two options are tunnelling or 'cut and cover'.
Tunnelling can be expensive, and you'd need to consider what the sub-grade is like, what length would need to be tunnelled, and how easy is it to find a willing contractor in that Switzerland. Getting a suitably experienced civils or groundworks contractor in Britain willing to take on a small, residential tunnelling job is fraught with difficulty. Most tunneller simply don't want to know.
So, that leaves cut & cover, but you would need a structural engineer to assess the slab to ensure it's suitable for cutting. Some slabs are so inherently structural that the cost of support works to carry loads while cutting takes place can be exceptionally scary.
In a simple case, it will be an unreinforced (unlikeley) slab or one that is only lightly reinforced for its own integrity, so you could cut through, excavate, install drainage, backfill and re-cast the cut section with appropriate tie-in dowels with relative ease.
If at all possible, the cut & cover would be the preferred option, but until you've explored the building's structure more fully, you can't really make an informed decision.
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