Basement Piping Connection. 3

[rra1990]

Good day!

I was hoping for a help for this piping drawing. As you can see on the attached drawing, this is the Basement floor plan, they use 4" pipe under slab for soil and waste piping line.
My problem with the Civil Engr. is that excavation is underway and I don't know how much depth for the pipe should be needed.

from the floor drain,clean out, and toilet how much pipe depth should we need, and they mention about "INVERT LEVEL AND FALL HEIGHT" of the pipes. I was thinking of 12" pipe depth (as per code?) from the floor clean out until connected to the sewage pit which is 2m depth, but the civil engr. said the slab is 200mm thick and another 500mm for something (i forget what it is called).

Any help is much appreciated. Thanks in advance and I'm looking forward to learn from you guys, Thanks!

 

[dicksewerrat]

What is the local minimum slope slope on the pipe? Talk to the inspector and a plumber.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[rra1990]

Sorry for the drawing but this is my actual case now.. I think the minimum slope of the pipe is 10%..

 

[PEDARRIN2]

Generally, you want 4"-6" of bedding (usually pea gravel or fine crushed rock) below your pipe. Ideally you would want the upper part of any fitting to be below the lowest part of your floor slab, although this is not critical. The horizontal portion of your piping should be below the lowest part of the slab, although this is also not critical. For this application, the slope of your pipe would be 1/8" vertical for every 1'-0" of horizontal travel, which is a lot less than 10%. Measure the distance from the furthest fixture to the sewage pit, multiply by 0.125, divide by 12. Add 4" for the slab, and 6" for the bedding and that is how deep the trench will be at the end. It will be slightly less deep at the fixtures, but not by a lot, unless the distance is great, i.e. >100'. The plumber may just fill in with more bedding rather than a deeper trench.

Hope that helps.

 

[rra1990]

@PEDARRIN2, thanks a lot sir! actually I'm reading some online plumbing notes earlier and i found out that a 4" pipe needs a 1/8" slope for every 1' of horizontal run, or 0.0833mm/m (right?)

I'm a bit confused about my first figure sir, because there is two(2) floor clean out in a single pipe, and that pipe again is connected straight to the sewage pit. Should i start the measurement at the 1st floor clean out, through the sewage pit?(which is 26.74 meters) or should I measure from the second floor clean out??(which is about 23 meters) Thanks sir. Appreciate it.

 

[PEDARRIN2]

Your calculation needs to be from the farthest fixture or vertical pipe from another floor that is the farthest from the pit.

Slope for horizontal pipe is always for the floor it is on. Once you go down a floor, you start the calculation over.

A fixture on an upper floor will run horizontal (with slope) until it turns vertical down to drop below the lower floor slab. It will turn horizontal as high (least depth) as it can. It then runs horizontal (with slope) to outside the building (pit).

 

[bimr]

Here is a link to a specification for trenching and backfill.

http://www2.iccsafe.org/states/virg.../Chapter 26_General Plumbing Requirements.pdf

Floor drains are usually 4-Inch Diameter, check the plumbing code. You also need a trap.

 

[dbill74]

from the floor drain,clean out, and toilet how much pipe depth should we need, and they mention about "INVERT LEVEL AND FALL HEIGHT" of the pipes. I was thinking of 12" pipe depth (as per code?) from the floor clean out until connected to the sewage pit which is 2m depth, but the civil engr. said the slab is 200mm thick and another 500mm for something (i forget what it is called).

A drain's INVERT is the elevation of the lowest point of the interior of the pipe. It is always going to be relative to something, most often it is to either the finished floor elevation or sea level. Civil engineers almost always work to sea level, this is important to coordinate to ensure you are communicating the right elevation the drain pipe is to be at when it goes from building engineer's responsibility to civil engineer's. A pipe's invert elevation does NOT take into account pipe wall thickness or pipe bedding in the trench.

The Fall height is simply the change in elevation of the drain pipe from the highest point to the lowest.

1/8" per 1' is 1% slope.

To calculate the invert of the drain at the pit you will need to first determine the depth of the highest pipe in the system. Figure in the slab thickness, slab bedding thickness and pipe size, you are looking at minimum invert (highest point) about 32" below top of slab or FFE; this will keep the horizontal piping out of the slab bedding material which is usually compressed sand. This is for your case presented here only, NOT a figure to be used for any other building. You will need to determine minimum invert for each project/drain line.

Once you have this, you can use PEDARRIN2's equation and length from highest/furthest point to pit to calculate the total change in invert (fall height) and thus the invert at the pit.

 

[rra1990]

@dbill74, as usual sir you are so informative, I remember you giving me also points and very helpful tips in the AC division. Thanks sir, I would like you to see my attached drawing, it is about what I understand about what you say, correct me if Im wrong sir. thanks.

 

[dbill74]

rra1990, you understand correctly. The only thing I would correct in your images is in regards to length of the vertical pipe. You have to remember that you have a cleanout at the top and an elbow fitting at the bottom. When you take into account the sizes of these items, the pipe connecting the two points will be less than 32". The total length, including the cleanout fitting and the elbow would be need to be at least 32".

A couple additional notes:
1) There is nothing that mandates the invert there be 32" below FFE, if it helps constructability/installation of other components or to avoid structural members, it can be more or less.
2) 700mm ~ 27.5" (it helps to work with all the units in the same unit set, SI (meters) of Imperial (feet/inches)) I try to avoid having horizontal piping in the bedding to avoid potential damage.
3) You are showing the tie in to the sewage pit low on the pit, this is in error, inflow to the pit should be as high as possible. This is to avoid water/sewage backing up into the inflow pipe. The sewage pit's outflow invert should be below the inflow invert. How much lower? It doesn't matter, 3-6" is recommended, if it's your design, it's your choice, if it is a manufactured item, the manufacturer will determine the difference in invert.

Glad I can help.

 

[rra1990]

@dbill74, thank you sir. yes regards to the length of the vertical pipe it should be equal to 32". it shout be lower because of fittings from the clean-out and elbow at the bottom.

about the tie to the sewage pit, Its not the actual connection hehe, I just draw my interpretation that way, btw thanks for the reminder about that sir. thank you very much for the help.

I found about this slope table last night while reading, is this recommended to use as an reference??

Also I found out about flowrate of the waste going through the pipes, it says too much slope will let the liquid drops faster than solid waste.. My question is, Is there a formula for the flowrate needed? I mean, is there any contradiction when using the 1/8" per 1' of slope compare to the flowrate? thanks!

 

[PEDARRIN2]

rra1990,

That reference is from a plumbing code. It is a requirement, not a recommendation. However, in actual installation, most of the time, 1/8" per foot for piping less than 3" diameter is accepted.

In general, it is not the flow rate that is a concern, but the velocity. Generally, you want at least 2 feet per second velocity to push solids through the pipe. I have also seen information that alludes to the excess slope. I am not sure how valid it is as a general rule.

Generally, you want to keep flow in a sewer pipe below 2/3 full, 1/2 is ideal.

Use the Manning Equation to determine flows/slopes/etc. You can do a web search and find many resources.

 

[ME27272727]

Excess slope mainly comes into play when regarding horizontal wet vents / combination waste vents / circuit vents.