Plumbing below a mat foundation

[theclipper]

I have a 10" mat foundation with #5 top and bottom 16" c/c supporting a 5-story cold formed metal frame dorm - any thoughts on how the underslab plumbing should be addressed. The mat has been modeled in RAM Concept - and I'm showing a worse case applied soil bearing pressure of around 2000 psf and I have an allowable of 4,000 psf. Thanks for any detailing thoughts/warnings/etc... in advance.

 

[wiktor]

Leave the openings in the slab to access and construct the plumbing. Once completed, plug the holes. Specify some kind of rebar splicers, and proper compaction of the fill material.

 

[bridgebuster]

Are you hanging the piping from the mat? In NYC the building codes requires this if the structure is a school facility.

 

[theclipper]

Not hanging - the pipes are mostly waste drains that will be installed and sleeved up through the mat.

thanks for your thoughts.

 

[oldestguy]

I've been involved with many such designs. Never have they left places for later placing pipes. Pipes go in first and the slab later. If concerns about differential settlement, then use more than the minimum slopes for the waste pipes.

 

[InDepth]

You could probably follow typical roadway specs where it's a minimum distance below the ground surface and surrounded by gravel. You could also verify that the specs indicate a minimum load rated pipe. For 2000 psf a HS20 load rated pipe may be satisfactory. It's kind of a best judgement based on load and the ability of the soil forces getting around the pipe by overstessing the soil adjacent. The mat can also span the distance typically.