I have described the project to tunnel under my house to correct a plugged drain under the slab 20' from the edge of the house. I posted the following thread a couple weeks ago detailing the procedure they took using a "tunnel rat" truck to dig a tunnel from the CO to the trouble spot and relay a new PVC pipe all the way back to the CO.

[www.plbg.com]

Three days ago inspector signed off on the rough inspection, engineer report for the "BEFORE" sand compaction came in and yesterday was the scheduled backfill. However after a few hours of waiting I called them and they said they were running behind so we rescheduled for today at 8am.

Well I was up bright and early at 8am, waiting to see this big truck shooting wet sand in the tunnel, I waited and waited and 11am still no truck. They told me they were "on their way" since 8:30am. But at 11am I had to leave to run some errands and when I got back at 1:30pm the job was done and the truck is gone. I was not able to take any pics!

However, yesterday I did talk to the company and they have taken pictures of the "BEFORE" and "AFTER" and after looking at the pictures I think I see what happened.

Here are some BEFORE pics.

This is the outside cleanout.



After the sand has been excavated showing the 3" pipe goes under the slab and to the left is the kitchen drain tie in, then goes further down and split at a combo. The branch of the combo connects to the line from the right coming from two bathrooms, and the top of the combo reduces to 2" and connects to the washing machine line.


The trouble spot is where this combo is. Sand seem to get trapped inside and it is always submerged from what we could see through the camera. A closer look further in:


Now I can see why there is sand in this combo. If you look at this:


From another angle:


See the 2" line being disconnected from the top of the combo? The tech told me this was the way they found it. Disconnected. It does not make sense. Seemed like someone forgotten to glue this joint? So what happened was when I do a load of laundry, the water is discharged into the 2" line and when it passed the gap, sand and dirt got pushed into the pipe and sat in that combo. My guess is as more and more dirt got pushed into that fitting and line, it created a void under the slab, and the combo fitting got heavier and heavier, so it sags lower and created a belly right there. As you can see from the pic below, the old hanger was holding up the pipe, but the upstream end towards the combo was sagging low.


Here is a pic of the guy in the tunnel removing the old pipe/fittings:


Now they are laying the new pipes:




Edited 1 times.

Here are some AFTER pics of the line.





A closer look at the new combo:


The new connection to the existing 3" line to the right and to the 2" washing machine line.




The PVC pipe was changed all the way from the combo to the outside CO.


Hanger every 4':


Next week is final inspection.



Edited 1 times.

Now my question is, any idea how that pipe could be disconnected like that?

It is not pulled apart from a fitting, the "break" is a perfect circle. I don't get it.

oh, they spilled primer too...LOL



I bet it was difficult with the smell of the primer when you spilled it in a tunnel with little ventilation.



Edited 1 times.

That in my book is plumbing nightmare story. Great to see the photos. Good to see that I surpassed crappy gluing finally. Like the previous post the fumes must have been nasty in that area. Your theory on how sand kept clogging the downstream fitting from the laundry sounds plausible.

Sum, This is not the first time someone has tunneled under your house. The clevis hangers are a give away. The pipe pulled apart because the last guy didn't repack the dirt enough. That is why the city wants all the reports.

In the Metro New Orleans area 1/4" stainless steel hangers are required on all under building slab sewer. (every 5' on cast iron andevery 4' on PVC) I am currently doing a (short) tunnel job and the adjustable hangers for under slab repairs are adjustable stainless steel.


I have used a service where they pressure wash the tunnel and suck out the mudwash with a vac truck.

It is hard to understand how the pipe broke perfectly clean looking like it did.


The final installation lookslike a quality job.

Good Luck



Edited 1 times.

The story of Sum's house is older now than all four of my grandkids. I am really at a loss for words. I think I can only offer one suggestion: Winnebago

sum, that pipe was not primed before the cement was applied and probably leaked since it was installed because as someone mentioned earlier it had been tunneled before leading me to believe it was a bad repair and the pipe pulled out either before or after the leak caused some of the sand to be washed away. the rest is most likely as you figured.

look closely and you can see the cement line on the pipe that tells me it had been inserted into the reducer at the combo but had pulled out at some point. a foundation repair in the past could also be the culprit

- - - - - - -

PLUMBERS "Protecting The Health Of The Nation"

So,Did they glue the riser?I give you even money the last repair of this line was not back filled properly.Many forget that pvc dwv will float.

I've never heard of, or seen, a tunnel under a house where they could "walk around it it". Usually it is a "crawl space" that you wiggle into and out of.

IF it had ever been connected, it should not have. Once it was together and the backfill placed, the only way it could come apart would be for the pipes to "move" laterally, and the dirt would have prevented that. It would have taken almost impossible movement to just get it out of the socket. It stretches our credibility for it to move almost 4". I had a job recently where it was obvious that the pipe had been damaged before it was assembled but was put together anyway and covered up.

that is my thought, exactly..
when the company blows the wet sand back into that tunnel, what is supposed to keep the pipes from being pushed backwards by the blowing sand.
they should install "thrust blocks" at every sideways joint and riser.

A1APLBG, I think you are right, there is no way an original installation back in 1981 (this is not my remodel house that was built in 1972, this is the home I am living in now), would use hangers before the slab was poured right? So something was done previously and was messed up? If so I wish I knew that because the previous repair was subpar then, what a waste to dig and tunnel to go through all that just to have a bad joint at the end.

dlh looking at the old joints looks like either they used all clear primer or they didn't prime? I wonder how strong that 45 is upstream of the repaired combo. Wish they had replaced that too.

They glued in the riser after I called them and told them before the inspector came out for rough inspection.

hj, another possibility was that the pipe was actually closer to the combo than indicated in the photo, but the act of hydro excavation perturbed the 2" pipe and when they took the picture in the tunnel it showed like that. I am not aware of any foundation repair, that was filed with the city and permitted.

A while back I went to the city to look up all the work done on the house that's been permitted.

Oh wait...If the pipe was previously repair via tunneling, and looking at the old pipe hangers it must have...and I don't see a permit, so it was done illegally. I have lived in this house for 10 years, this repair is more than 10 years old. The previous owner probably hired someone to do this work off the side, and the guys I hired told me this hydro tunnel and backfill is fairly recent, it could be they used the traditional digging approach and really have no way to backfill properly to the original compaction and just shove dirt back in the tunnel best they could. Is that possible?

Packy, I wanted to be there to observe the process and take pics, but they showed up late so I missed it. From what the tech told me, they actually go back into the tunnel with the giant hose, and will direct the hose to shoot the wet sand. The sand is a special sand and the moisture control is very precise to get to the desired compaction factor. He points the hose inside for it to shoot and he said the pipes will stay put. I wonder too, when he shoots that sand to the 2" pipe, whether it would bust that 45 apart during the act of backfilling.

Sum, I am concerned about support for the pipes of course. i think that is one of the factors in the separation of the 2 inch pipe. (probably had an inferior welded joint also..) If you look the support had rusted thru and the pipe sagged just after the connection and put a lot of stress on the weld. Of course the connection is the weakest link in the whole pipe. I think the new sand fill method sounds pretty good.

I like the idea of stainless supports.. but you pay for them.. However you probably wouldn't have had to have a tunnel under the house to fix a break so maybe the stainless would have paid for themselves..

Thanks for the pics

best they could do? hand tamping to compression level is not what happened,Or at least dose not look like it.In higher water table areas you better have your ducks in a row!!!

You know my thoughts. . . . . . a big pipe separation and no sewer odor. Great pics and best of luck>

They COULD have installed the hangers with the rods up into where the concrete would be, and then poured the concrete floor around them, if there were questions about the soil quality. The only way to tell would have been to look at the anchors and see if they were drilled or embedded.

I think the whole thing about the soil density and compaction thing is flawed. Not the requirements to have the same soil compaction, but how the city executes that requirements.

The contractor was required to hire an engineering company to do a soil compaction test before and after the excavation and backfill to prove to the city that they dug the tunnel and backfilled the soil with a compaction/density that is equal or higher.

The engineer came by to extract a soil sample, I don't know where the sample was taken, I was not home. A compaction report was done, sent to the city with the permit application, and once they got the notice of commencement, they dug the tunnel with the hydraulic tunnel rat and made the repair. Note that when they dug the tunnel, they first dug an access hole about 3'x3'x3' deep. The soil from that digging was piled to one side, as shown in the diagram below. When the tunnel rat started shooting water into the tunnel and the hose sucking up all that soupy water, the soil in the tunnel went back into the truck for disposal.

When they came back to fill the tunnel, the wet sand was blasted into the tunnel and filled to the end of the tunnel, as shown below in orange color.



Then they took the pile of dirt from the original access hole, pushed it back into the access hole, wet the soil down and compacted it with a 4x4 log. Now the access hole is completely covered and the sand inside the tunnel.

This week the engineer will come again, take a sample and provide a report to the city of the "AFTER" compaction/density. Now just where will he take a sample? core out a piece of the soil in the access hole? But that has absolutely nothing to do with the sand in the tunnel!

In order to get the true compaction of the tunnel backfill he needs to remove the access hole dirt and get a sample of the sand inside the tunnel right? Otherwise he is comparing apples and oranges, right?

But the city wouldn't know, the city would just look at two reports, before and after.



Edited 1 times.

NOrmally, the city does not care what the compaction level is BEFORE the repair. They want to know that the replacement soil is compacted to 95%. And that is a function of the soil they replace NOT the original soil.

but hj, the critical parameter is the compaction of the sand under the tunnel, and not the soil outside of the house that was dug for the access hole. The sand was blasted in via a hose, and the access hole was backfilled manually with a shovel and compacted with a 4x4 log.

Doing a sample on the access hole does not say anything about how compact the tunnel sand is.

if the wet sand totally filled the tunnel you dont need to worry about the compaction as it will be pretty hard and naturally compacted. but if the access holes dirt is to lose it will allow the sand to get wet and filter out from under your house through the loose soil

- - - - - - -

PLUMBERS "Protecting The Health Of The Nation"

I know, but I thought the compaction that is critical is the sand compaction that is under the slab, not the compaction of the backfill to the access hole that they dug which is outside. Heck next week I might dig that up to plant a few shrubs and that itself would "disturb" the compaction of that area. Just doesn't seem logical to go through all that trouble, when the city analyzes two soil reports before/after and the "before" was original dirt in the tunnel, and the "after" is the backfill dirt of the access hole.

I just looked at my permit and under the title "DESCRIPTION OF WORK" the contractor put down "Repair/Replace Domestic Water Lines".

I thought that is odd and asked the tech, and he said this is EXACTLY the wording the city requires. In fact they had down "REPAIR RESIDENTIAL MAIN DRAIN" and they city rejected it and asked them to change it to this. I thought "water lines" typically refers to supply lines, no?

sum, if the sand is still wet and they pack that dirt properly it will actually pack the sand also.

yes that is weird. it should have read "replace building drain" and there is no reason for the city to reject it other than it was an @#$%& that didnt know what they meant or they just wanted to be difficult for some reason

- - - - - - -

PLUMBERS "Protecting The Health Of The Nation"

OK today the inspector came by for the final inspection and it past.

The inspector signed off the permit and did corrected the description of work. Remember I said it stated "REPAIR/REPLACE DOMESTIC WATER LINES"? Well the inspector crossed out "WATER" and wrote "waste" over it. He said they wanted it to say "REPAIR/REPLACE DOMESTIC WASTE LINES" but the tech probably wrote "waste" and the contractor used a secretary to type and she typed "water" instead. So that explains it.

Sum.the footer is the only important part,you live in a/momolithic slab \home!!!the only needed test is under or at this footer area.Your city seems to be easy going.not the best case.the dwv/ building drain \was repaired and if you need to go to court later .print these words so you have a professional statement.The building sewer is after five feet from the foundation of your home.I have seen the dirt separation on remodels that had no leaks!It is settling.the footer deep concrete along the edges and drops of concrete height is where your home supports it,s weight.You look good to go and hope .your next home serves you better.