Sawcutting a two-way slab

[csellc1]

I have a project in which the slab-on-grade is an 8" thick two-way flat plate slab.

The building is being renovated and the Mechanical Engineer has shown the existing slab being saw cut and trenched to install new under slab plumbing. There are at least two trenches that run the length of the building and also a few that run the width of the building. The width of the trench is about 2 feet.

I am having a hard time figuring out a way to have the slab repaired after the plumbing is installed to behave as a two-way structural slab again.

Any ideas or guidance would be appreciated.

 

[Inlander]

Why not? Can you flow fill to the bottom of the pipe? I don't think the soil will settle under the plumbing weight. Your slab is independent anyway. If you have holes at say every 10', you should be able to adjust it and bed it with a flow fill. This should all be the MEP's job right? You just need to figure out a suitable way to access it. I hope the rebar spacing is wide enough. If not, maybe you can justify a couple of cuts & epoxy some new bars.

 

[demayeng]

How about drilling new piles through the fill along the centreline of each trench, then creating a U-shaped headstock (from reinforced concrete) on each pile that supports the slab on each side yet also allows the plumbing to be installed later.

The pile spacing will be dependent on how far your slab can span.

 

[SkiisAndBikes]

How about using hydrodemolition equipment? The hydro equipment could be set up to take a 4'-0" width of concrete out, leaving all the rebar in place (and cleaning it up to). The location of the trench within the span would have to be considered carefully, hopefully the mechanical would have some flexibility. The mechanical engineer would be left to figure out how to trench under the existing rebar, perhaps the odd transverse rebar could be cut out periodically, then replaced with dowels. Perhaps a vacuum truck could be utilized to remove enough subgrade to place a bedding for the pipe. The excavation could be left open for the building inspector to review. Place trench fill around the drain pipe, up to the underside of the slab, then repour utilizing good concrete repair practices for preparing the sides, bonding agents, etc...

The disadvantages to hydrodemolition are usually related to the amount of slurry they produce (don't let it go down existing drains), noise and cost. However, I would bet it would be cheaper than removing the slab.

Anywhere near my area, where building foundations have to be supported by piles, so do the services, otherwise you get a lot of cracked water/sewer lines. Has the mechanical considered this?

 

[csd72]

If you use plastic pipe and a pumped line then I fail to see the issue with a little settlement. Use rocker pipe joints to avoid issues at the joints but other than that the pump will pump a gradually curved pipe just as good as a straight one.

If it still worries you then you can use the holes mentioned above to fix hangers around the pipe and hang it from the slab.