Reason for encasing drainage pipes in concrete ?

[coxsox]

Can someone tell me the reason for encasing drainage pipes in concrete when they run under an extension. Is this for structural reasons, i.e. the possible loading on the pipes. I presume its nothing to do with possible leakage ?

I am constructing a raft foundation and have found storm water drainage about 500mm below where the raft will sit. I know these pipes can stay in place, just unsure whether I need to encase them in concrete, especially as the raft will be one big lintel over this pipe, if you see what I mean.

Any help appreciated, thanks.

 

[cotswoldbuilders]

I think the drains are usually wrapped in insulation to allow for any movement, or extra weight bearing on them.

 

[noseall]

Modern day drains would only be surrounded in concrete where they are subject to vehicular traffic i.e. driveways etc.

We have also come across a lot of earlier salt glaze drains whereby all the drains have been covered with concrete, no doubt to add some stiffness to the pipe runs.

Where a drain passes through a building, the drain pipes should be allowed to remain intact regardless of the building movement. Therefore they should either be lintelled over or wrapped in compressible material so that the building or its foundations have no influence upon the drains, should it settle.

All other drains are surrounded in pea gravel or similar.

 

[stuart45]

Salt glaze were always surrounded with concrete as the joints were not flexible, so any movement could break the joints and cause a leak.

 

[coxsox]

Where a drain passes through a building, the drain pipes should be allowed to remain intact regardless of the building movement. Therefore they should either be lintelled over or wrapped in compressible material so that the building or its foundations have no influence upon the drains, should it settle.

All other drains are surrounded in pea gravel or similar.

Thanks, so if the existing drain pipes are laid in pea shingle underground and between the pipes and raft is type 1, soil and clay, then I presume they are ok left as is as any movement on the raft will be absorbed by the materials in between the pipes and raft, thanks