New 8-ft deep lift station being installed in existing building

[Grant M]

Hi all,

As part of a project in an existing manufacturing facility, the wastewater system is being upgraded. As part of this, (3) new 8-ft deep lift stations are being installed within the existing facility. We will be sawcutting and removing the existing concrete slab-on-grade, then excavating to the required depth to set the circular FRP lift stations in, followed by backfilling around them and repouring the concrete slab for a finished surface.

However, I have concerns about potential undercutting of the existing slab-on-grade floor. I haven't really dealt with a situation like this before, so I was wondering if anyone had any suggestions of how to best handle this, or is this something that is typically just put on the contractor as their responsibility?

Thanks!

 

[TRAK.Structural]

I would make the perimeter of the sawcut area a few feet beyond the limits of the excavation on each side. This way if some of the soils around the edges of the excavation are disturbed it won't undermine the slab subgrade.

 

[HTURKAK]

My points ,
- Keep far away from the footings ,
-Consider shoring the excavation pit..

 

[Grant M]

My points ,
- Keep far away from the footings ,
-Consider shoring the excavation pit..

Unfortunately, it may come close to an existing footing but this facility is so old (early 1900s) and has no record drawings to verify foundation sizes and locations. I think I will plan on including verbiage to the contractor to "provide necessary shoring and bracing of excavation, and underpinning of existing foundation element(s) if encountered during excavation work".