Tying into gravity sewer with gravity sewer

[Plumber John]

This might be a simple question, but I'm simple. I ran a 6" pvc gravity sanitary sewer about 80' out into the right of way where the city sewer is located. We are about 6ft deep out near our desired tie in location. The city sewer is 16 feet deep, so we are dropping 10' into an 18" clay (very old) gravity sewer line. We tapped into the top of the clay and used a product that I've not used before, then encased the connection point in concrete.

My question, since we are dropping 10' or so, is there a problem dropping straight down into the main? Our connection is a straight tee not a wye and we're going to have a cleanout access directly above the deep connection point using a wye and 45° in place of a 90 to drop down.

Any issue with that? The city engineer mentioned something about tying in at a 45° angle but that's not practical with all of the other obstructions and dangers at play.

 

[swazimatt]

The norm is to connect with a London Junction as I suppose it will direct the discharge in the direction of flow as per the detail below. As you can see it does not involve much additional space as it is the last foot or two that is the 45. For old/in use clay pipes you can get a saddle connection (below) that does the same without having to break the whole pipe.


To answer your question, they are both pretty large pipes so should have decent flows in them and i doubt wastewater dropping in at90 will make little difference to 45 in the grand scheme of things

 

[LittleInch]

The issue is impact force on a fragile, brittle pipe.

 

[Plumber John]

FatBoy, SDR 26, SDR 35 Gasketed Bell Gravity Applications Inserta Tee Detail

The drawing gives information on an Inserta Tee® FatBoy, SDR 26, SDR 35 connection for gasketed bell gravity applications.

www.adspipe.com

Is the product we used. I also thought that the 90 riser traveling to the surface might have detrimental down force on top of the clay pipe.

The reason we switched from a rubber banded saddle to the product linked above was, we literally couldn't get the stainless clamps around the 18" clay pipe. As water infiltration and sand flowing under and around the very wide pipe was making it a losing battle. Being 16' down in the ground isn't a great feeling. The ditch wasn't properly sloped with all (4) the fiber optic lines, telephone (copper) lines, gas lines (2) and concrete storm piping in our 16' wide grassy area. We had a ditch box but the top of it was still 10' down below the surface.

Along with the product linked above we poured concrete around the connection padded with clean rock on both sides of the clay pipe to give it some resistance to lateral force and possibly spread the down force. I'm just a plumber but I think it'll hold up.

This clay pipe actually needs replaced as I'm pretty sure we tied onto an area that was sagged. I happened to do a different sewer tie in down stream from this, but on the same line and it had similar "standing full" issues.

 

[HTURKAK]

I would prefer sloped connection rather than drop type. I assume recommended proctice would be concrete protection of collector and riser. The saddle or proposed connection fitting should be connected with 45 degr with vertical .
The following figure from the book Gravity Sanitary Sewer ( Edited by Paul Bizier ).

 

[GD2]

OP,
How about preventing the airlock in the 6" gravity sewer itself? You are connecting it vertically down to the main.

 

[Plumber John]

The Yes tied in vertically. The picture shows the horizontal to vertical connection after 10 ft of backfill on the vertical portion of the tie in.

From the 6"x4" increaser up is for cleanout access which is not really necessary or practical, but the man in charge said we should do it.

I think an air lock is unlikely due to normal vent connections inside of the building near the traps and large city main below. Airflow in and out should be plenty, I would think. Although I haven't been inside to see what size or how many vented traps they have. I don't have a picture of the actual tie in connection, but I directed some light into the 4" pvc riser and can see down into the city sewer and all appears fine so far.

 

[pierreick]

Hi,
It might be worth to read this document about gravity flow.
Pierre