keeping the rough from wandering

[jimbrill]

hi. looking for some advice, thanks. we’re laying down the rough of PVC on a dirt floor and then covering with 6” gravel, 2” insulation, and a 4” concrete slab.

how do I lock in the PVC so it doesn’t move around when we’re shoveling in the gravel?

I was thinking of taking 1/4” rebar and bending it to fit the OD and use it to lock in
the PVC to the ground, but maybe overthinking this? what’s the best practice?

 

[breplum]

On plastic pipe we use wooden stakes driven into soil on the sides, plus crossing angled ones to keep from bowing up.
We like base rock (NOT drain rock) tamped down firmly if soil is disturbed below the pipe.
Too many disaster cases (forensically referencing) of plastic pipe going out of slope where the soil is not stable and suitably compacted underneath.
Rebar on cast iron piping in slab is great, but might ultimately grind through from expansion and contraction against plastic.

 

[jimbrill]

awesome- thanks @breplum for the intel and guideance!! makes a ton of sense.

will make sure the gravel will be base and have no fines. our dirt is pretty even and I’m thinking about laying down a path of tamped sand where ever we lay the PVC. our dirt is so dense it needs a 20 pound hammer to soften it up. Can I add pointed 2x4 stakes on both sides every 4’ with the crossing peices attached on either side with wire? or are you suggesting that we drive the stakes into the ground at 45’, over the pipe on alternating sides?

 

[MicEd69]

Using 2x4 stakes is a bit much to use for anchoring the PVC pipe. A piece of wood ripped 3/4" sqaure is entirely adequate. And I have always laid the PVC on a compacted sand bed and covered/encased the PVC with sand as well. Lay the sand and compact it to the slope required for the sewer lines. Lay the PVC on the sand base and install a few vertically stakes to keep the PVC in position. You can add a few stakes at an angle to keep the PVC in contact with the sand base or use wire to hold it down across two vertical stakes. Install the gravel base, but do not cover the PVC pipe with gravel, leaving "trench" in the gravel along the PVC. Then fill that "trench" with sand to ~1" over the top of the PVC. Hand tamp the sand tight around the PVC, just don't go overboard with the tamper. At this point, if you used wires to hold the PVC in place, I would cut them as the sand will maintain the appropriate slope of the PVC. Add gravel over the sand to the design elevation. Then you can add insulation, if that is your design, the vapor barrier, and then place the concrete.

 

[jimbrill]

thanks so much MicEd69!!

our soil is very dense and we needed a 20 pound hammer to loosen it up enough to get a shovel in during excavation. your instructions are seriously valuable. thanks. was thinking about replacing the 3/4” stakes with 1/2” rebar that is sleeved with 1/2” PVC where it is in contact with the pipe. the rebar still needs a masons hammer to drive it but at least we can get it into the ground. we would use wire to hold it against the sand and as you said, remove it after. what do you think of that tweak?

 

[MicEd69]

That seems very reasonable and a good idea. With that hard of a base, once you get the pipe in place and covered with the sand and gravel, it's pretty well held in place with that covering. Just be careful around the piping when you are placing the concrete. And the PCV on PVC contact would eliminate the concerns that Breplum and I share about steel against PVC causing problems during expansion and contraction that does occur in under slab piping.

Been there with extremely hard dirt under a basement floor. I installed a sump in an existing basement with ground that hard. I thought about using my gas-powered post hole digger, but just toughed it through using shovels and a manual post hole digger.

 

[Twowaxhack]

We do it like this. The trench isn’t over excavated, solid flat bottom. Safe off the pipe by standing on it and backfilling by hand to the top of the pipe. Tamp and recheck grade with a laser. Then slowly fill in with the trachoe.

 

[MicEd69]

Nice procedure for an outside sewer installation on a house without a basement Twowaxhack. However, this post was asking about rough-in plumbing installation in an existing basement where the old floor has been removed.

 

[Twowaxhack]

Nice procedure for an outside sewer installation on a house without a basement Twowaxhack. However, this post was asking about rough-in plumbing installation in an existing basement where the old floor has been removed.

The house in the pics I posted has a basement, but it is outside. Good eye.

But that doesn’t matter, we do the same procedure for slab jobs. New houses or replacement. If we can’t get equipment in the area then we hand dig.

Under parking lots, slabs, and sidewalks.

Over the years our company has replace over 9,000 sewers snd house drains in our work area.

 

[MicEd69]

Sorry for the confusion. From the pictures you provided, it just looks like that sewer line isn't near deep enough to come from under a basement slab. It only looks like it's 3-4 feet below what I would guess is the first-floor elevation. Must be an optical illusion and the trench must be more like 7-8 feet deep, huh?

 

[Twowaxhack]

Sorry for the confusion. From the pictures you provided, it just looks like that sewer line isn't near deep enough to come from under a basement slab. It only looks like it's 3-4 feet below what I would guess is the first-floor elevation. Must be an optical illusion and the trench must be more like 7-8 feet deep, huh?

No the pipe in my pic is not coming from a basement.

The pipe doesn’t know that though.

Sewer pipes I’ve laid in gravel do not seem to move. It’s just has never been a problem for us.

 

[Twowaxhack]

We’ve discontinued a lot of septic systems and installled sewers to the public utility.

The new pipe is installed through the old drain field where there is a lot of gravel when we’ve backfilled.

It works great if you don’t over excavate.

Our main guy that digs uses the Trimble system on his boom to insure he’s not digging too deep. Then we compact the ground.

We maintain a perfect 2% grade.

Everything is checked with lasers and inspected by the city.

 

[jimbrill]

That seems very reasonable and a good idea. With that hard of a base, once you get the pipe in place and covered with the sand and gravel, it's pretty well held in place with that covering. Just be careful around the piping when you are placing the concrete. And the PCV on PVC contact would eliminate the concerns that Breplum and I share about steel against PVC causing problems during expansion and contraction that does occur in under slab piping.

Been there with extremely hard dirt under a basement floor. I installed a sump in an existing basement with ground that hard. I thought about using my gas-powered post hole digger, but just toughed it through using shovels and a manual post hole digger.

@MicEd69; thank you. I'll get after it as described - it's a relief to have this forum to turn to, thanks all!

 

[Twowaxhack]

I'll get after it as described - it's a relief to have this forum to turn to, thanks all!

I think you’ll find that your pipe isn’t going to move around if you place the gravel along the sides of it with a shovel until you’re even with the top of the pipe if your base is solid.

 

[jimbrill]

thanks, Twowaxhack.

Yet another issue would be the erosion of the soil base under the pipe and assembly over time, but given our soil condition, I think we should be ok.

 

[Twowaxhack]

thanks, Twowaxhack.

Yet another issue would be the erosion of the soil base under the pipe and assembly over time, but given our soil condition, I think we should be ok.

I’d be concerned also if the dirt under my foundation was eroding.

On beach houses that are on pilings and have a concrete slab under them, we install pipe hangers and when the slab is poured the hangers harden into the slab.

When hurricanes come through and the sand washes out from under the slabs, the pipe hangers hold the pipe in perfect alignment.

Holes are then drilled into the slab and the void is pumped full of jacking mud.

 

[breplum]

jimbrill (OP), road base (to my memory) does have fines (rock dust) included, that allows it to compact well (as compared to drain rock or gravel w/o fines).