How far should cement ring well be from building wall

Question

I have a Residential building(India) which has no space in both front and back yard. It's a newly built two storey building( 3 houses ). There is 5 feet space available parallel to building wall.

As the sand is clay , I couldn't do soakway to drain the sewage water hence I'm planning to dig three 2.5 ft width cement well ring for 10 feet depth and 5 feet distance from each well and 1.5 feet from building wall. so sewage water from each house will go it's individual cement ring well.

I really feel this can solve my sewage water issue.

But I'm really worried whether it could affect my building as soil underneath can loosen.

Please give me suggestions

FYI: Click here to read building tilt accident

Basically a borewell nearby the building has weakened the foundation of the building and has caused building to tilt.

Answer 1

A rough idea:

1. Bore and install a pipe as the rate of water dissipation in the onsite soil (permeability) test well. Fill the pipe and time the change of water depth at a later time. After a few trials, you can get a pretty good idea of how fast the water will dissipate, so you can size the volume of the wastewater collector/processor chamber to fit your needs (with a safety factor).

2. I suggest the system shall include a 2.5' I.D. settlement basin to catch large/heavy particles and the floating grease. Then connect the settlement basin to the main collector through a metal pipe. The collector shall be a concrete box with an open, or perforated, base to allow the water to dissipate freely. It should be sitting on top of a thick layer of gravel. The box shall have a 2.5' wall-to-wall clear distance, its length depends on the result from the water dissipation test and your need/goal.

I think you can fit this system in between columns so as not to disturb the foundations. Also, the change in groundwater elevations will be kept to a minimum, so there is no risk in building settlement due to groundwater overdrawn.

Best of all, you can expand this system at a later date shall the demand change. And you can always pump out water from the overflow pipe if necessary.

Please do discuss with an engineer, who might come up with a plan that best suits your situation and local practices. I am surprised at what your civil engineer has suggested unless the onsite soil posses a good permeability as indicated in the chart below.

http://www.clean-water-for-laymen.com/soil-permeability.html

Answer 2

Most sanitary sewer systems drain directly into a sanitary sewerline. If one is not available then a drainfield can be designed based on the type of soil, quantity of sewage expected, etc.

If you use a cement ring design that is not properly designed and sealed, then the sanitary liquid could either leak through the cracks in the rings and wash the soil away overtime or sanitary material (paper, debris, etc.) could plug all the cracks and cause the pit to overflow over time.

Regardless, having the pits so close to the foundation can accelerate a failure by contamination or washing the soil (soil fines) away from the foundation, including your neighbors foundation. I wouldn’t do it without a sanitary engineer designing the system.