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 Evaluating bids for removeing badly deteriorating cast iron pipes under slab foundation house and to replace with schedule 40 PVC
Author: Regina Burns (TX)

Three bids.

Two strongly recommend tunneling under house and replacing old pipe with schedule 40 PVC the is anchored and supported on stainless steel hangers every 3ft.Mud packed backfill with engineering compaction report. There are three entry points on all bids.

Only one bid recommends partial tunneling combined with a rerouting all new pipes to a y location that then would connect to city sewer.

Basically wanting to know if anyone has experience with either of these options, tunneling replacement all under slab or partial tunneling and rerouting outside the home to a main city sewer line?


Edited 1 times.

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 Re: Evaluating bids for removeing badly deteriorating cast iron pipes under slab foundation house and to replace with schedule 40 PVC
Author: hj (AZ)

I would have to see the job so I would know WHERE the various connections are located.

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 Re: Evaluating bids for removeing badly deteriorating cast iron pipes under slab foundation house and to replace with schedule 40 PVC
Author: bernabeu (SC)


..... with engineering compaction report.

YOU should obtain the report INDEPENDANTLY of the contractors.

Use ONLY licensed, BONDED, insured contractor with 'release of bond' contingent on satisfactory report.


"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

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 Re: Evaluating bids for removeing badly deteriorating cast iron pipes under slab foundation house and to replace with schedule 40 PVC
Author: sum (FL)

I had a issue with a broken fitting some years ago and due to many reasons we went with a tunnel fix.
But basically it involves:

(1) Dig a big hole 4' deep where the main line exits the house - This is required by city building code, cannot dig at the closet spot, must start at the cleanout.

(2) Big monster truck come and workers go down to the 4' deep pit, with two giant hoses. One worker shoots high pressure water horizontally, creating a hole to form the tunnel, the other worker holding a hose that sucks the slurry muddy water into the monster truck. They made a 25' long tunnel, about 3-4' in diameter in about six hours. They followed the pipe until the trouble spot is found (we already did a camera job so know approximately where).

(3) A soil engineer came and took a sample of the soil in the tunnel.

(4) The sewer line was repaired and new pipe hangers installed.

(5) City inspector came out to inspect, and decided that he wouldn't crawl into the tunnel. So he ordered the crew to send someone down there to snap pictures for him.

(6) After seeing the pictures, city inspector says he can't tell if the pipe is sloped properly, ordered the crew to go back into the tunnel, put a torpedo level on the pipe, and take the picture again with the picture clearly showing the pipe and the bubble on the torpedo level. Inspector passed the plumbing job.

(7) The next day another monster truck came and it contains compacted wet sand, the giant hose came out again and shot the wet sand back into the tunnel, until the tunnel was filled up. The original 4' pit was not filled back in, that had to wait.

(8) After a week, the soil engineer came back out and took a soil sample from a spot near the project excavation. I asked him why he didn't take a sample of the wet sand inside the tunnel, he said what he was doing was standard procedure.

(9) The city required the new soil density to be at least as compacted as the original soil density. The new soil sample was collected not inside the tunnel but at a near by spot. Which is crazy. The soil compact analysis report, which the city required to sign off the final permit, was $5000. Which was a total waste of money. Now yours truly, who is a structural engineer by trade, called up a buddy who is a geotech and asked why am I spending $5000 for a total bogus report...learned that this is how the city works, covering their asses, the soil compaction report says you are good to go, OK...

The whole project cost I think about 20K.

Now in FLORIDA the soil is mostly sandy and the pipe is shallow. So the tunneling may be much easier. Most of the cost is in excavation and backfill and the engineering soil density report. The actual plumbing cost is very small.

My question would be for the bids that involve several points of entry, does that mean you are creating several tunnels at the same time? My concern with multiple points of entry is you are likely to run into footings and grade beams that block your tunnel that you have to cut or break. I would review, if you have any original foundation plans, to make sure you don't compromise the footings. Our city allows ONE point of entry from the main cleanout where the pipe exits, that's it, from there you go in and you can branch off inside but cannot create more points of entry. If this is a repipe you have to hollow out the entire pipe network anyway so what is the reason for multiple points of entry except the crew can get to the inside work area quicker? But if you have to break footings for that? I would advise against it, because tunneling is already compromising the slab support some, but the footings are what really holds up your slab, weakening that would be a big concern.

Here are some threads that documented my previous tunnel process.



Regarding the engineering report for the soil density, that was costly and turned out to be a useless liability waiver for the city.

Edited 2 times.

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