setting a manhole

Hey I'm new to the forum and looking for some advice. A guy wants me to do a bid for moving his septic lift station under slab to a new manhole just outside the house. Not sure how to bid this project because it seems there are too many unknowns. Also it is very tight, only 20' to other duplex with property line at only 10'. Doesn't look like any utilities to dig around. The other problem is that to get to the pipe in the tank in the house I will have to dig below the bottom of foundation by a couple of feet which this house has the prefab walls bolted together on the corners and sitting on 3-4' of 3/4 washed rock. So i'm afraid of undermining a bunch of that wall and slab. Any thoughts? Also I'm trying to do this with the smallest hoe I can with being able to still set that manhole base safely, roughly 6600lbs. What size of hoe?

Thanks for any help

Advice, Anybody?

Sounds like a pain.Is there anyway to cut the slab and work from the inside?I would try to figure out how NOT to undermine the slab.I dont think you could backfill it without leaving a void of some kind.Seems like a small space to put in a big manhole.Throw lots of money at it,and cover you butt!

unfortunately you can't do much inside this basement. the room the tank is in is only 5'x5' and the entire basement is finished.
Thats what i was afraid of is undermining the slab and wall.


What size of track hoe would set the 6600lb base down in the hole safely??

Not that familiar with your building systems but I would look at getting a bonded engineer to advise you .........

sitting on 3-4' of 3/4 washed rock this you may be able to stabilize this by injecting a cement grout at least a month prior to excavating, this time is needed to allow the cement grout to reach max strength before you dig................