Sewer pipes under slab

stefcep · Aug 26, 2023 3:35 pm

Hello all,

We're at the design stage.

Its a knockdown rebuild on highly reactive clay soil. We have an engineered raft slab design, with beam footings spec'ed at 700mm minimum from top of floor to bottom of footing or at least 100mm into solid ground

One design option will require a sewer pipe running under the slab across the house for about 13 metres basically from one side of the house across to the other. I'm worried about soil movement that might later damage this pipe. Anyone have any experience or opinion if this a valid concern or am I overthinking it?

Pulse · Aug 27, 2023 10:24 am

stefcep

Hello all,

We're at the design stage.

Its a knockdown rebuild on highly reactive clay soil. We have an engineered raft slab design, with beam footings spec'ed at 700mm minimum from top of floor to bottom of footing or at least 100mm into solid ground

One design option will require a sewer pipe running under the slab across the house for about 13 metres basically from one side of the house across to the other. I'm worried about soil movement that might later damage this pipe. Anyone have any experience or opinion if this a valid concern or am I overthinking it?

I’m not an expert but your plumber needs to be on the ball. Reactive sites need articulated joints in the pipe and extra lagging when they go through the beams to allow for more differential movement. Have a look at AS3500. the pipe also should be backfilled with imported material.

building-expert · Aug 27, 2023 11:48 am

That is a question your engineer needs to answer in the design detail.

SaveH2O · Aug 27, 2023 12:02 pm

Below is a link to a post by a leading slab heave expert.

viewtopic.php?p=1206402#p1206402

Also, if AS 2870 is referenced in the contract, make sure it is not only referenced to the slab which is construction. It must also be referenced as plumbing if you want to include flexible joints etc.

stefcep · Aug 27, 2023 1:14 pm

SaveH2O

Below is a link to a post by a leading slab heave expert.

viewtopic.php?p=1206402#p1206402

Also, if AS 2870 is referenced in the contract, make sure it is not only referenced to the slab which is construction. It must also be referenced as plumbing if you want to include flexible joints etc.

Thanks that link in particular is really useful.