Sewer line replacement

Recent video inspection revealed that my 40 year old cast iron pipe under the concrete slab is deteriated to the point of needing total replacement. Some spots the bottom has reduced to nothing, some spots the corrosion build up looks like the inside of a cave...two independent video inspections recommend total line replacement.
I have not yet done the finished flooring in the house, so I guess it's good news I found out now.
In order to replace the entire underground line, I can find a way to determine exactly where it is (no, no records in the city I checked already), and cut up the slab and hope for the best. Or I can just ignore where the existing line is and just design a new route.
It seems designing a new route but tying in existing bathroom group has the advantage of not having to pinpoint exact locations of the line but only specific locations where the existing bath groups tie in. And since I am doing remodeling, 3 of the 4 baths I know where they tie in and I have not backfill with concrete yet.
Doing a new line has the advantage of avoiding cutting a trench across existing walls, I can possibly cut a line along a hallway in a straight shot, but run the risk of running into other pipes below grade that may be in the way (pool pump lines, supply lines, deck drain lines, roof drain lines).
What is the ramification to the structure of the slab is it's a 90'x90' slab and I cut a 90' lone trench across it?
Is there any sense in not making a single 90' cut, but say 8 10' cuts with several 2' sections uncut and I try to bridge under it will that "hurt" the structure any less?
I am laying in new 4" PVC pipe so the trench would be around 6" wide only except where I am doing tie ins.
Thanks in advance,
MC
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given the obstructions have you priced having the existing line cleaned and lined?
a plastic liner is inserted and expanded with hot water which cures the line creating a seemless line.
might be a affordable alternative saving lots of restoration work
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wrote:

I might consider a single "lined" water pipe running across a foundation.
Never would I consider it for a sewer pipe. His permit office can help.
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wrote:

The existing line is 3" cast iron. In most spots it's already corroded to the point the cross section is not even circular. I was told cleaning it with a snake will probably cause the pipe to collapse further/
The lining, if it works, I was told, will end up creating a non-circular pipe hugging the shape of the existing condition.
I have 4 baths, 1 kitchen, 1 utility, and one outdoor kitchen tie in along the way, those tie in locations have to be totally cut up because the liner would block all six tie in points. So they have to be opened up to cut the opening because there is no way to cut some of these tie in where they are 2" in size. If I make 6 large holes along the way, it's almost like doing 60% of the work.
MC
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On Sun, 21 Jun 2009 18:00:23 -0400, "MiamiCuse"
If this is Coconut Grove, Fl follow the local ordinances.
Pic of the "grove":
http://www.scrapbooksuperstars.com/wp-content/uploads/map_coconut_grove.gif
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MC-
Instead of cut, dig & re-route OR relining the old pipe........I would suggest looking into "pipe bursting" replacement.
I'd much rather dig 6 holes to tie into a "pipe bursting" installed new line rather than cut, trench and replace. But you have a better idea of the layout.
Digging a deep but narrow trench is a real PITA.....how deep will the trench need to be?
My neighbot had his line replaced via pipe pbursting....about 70' from sidewalk to sewer line exit from house.
cheers Bob
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You could bore under the slab and push the pipe from outside. you would have to do several bores to accommodate the various drains and an excavation to tie it all together.
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MiamiCuse | 2009-06-21 | 1:55:58 PM wrote:

Is it a post-tensioned slab? A long cut would compromise the cables.
--
Steve Bell
New Life Home Improvement
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Just 4" thick concrete slab, I have cut open a few spots in bathrooms for plumbing relocation and all I found so far were embedded wire meshes but no rebar no cables. Soil underneath is basically sand. Thanx.
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