Questions about back drop manholes

[aa44]

I am about to build a new house where the foul water drain connection will be to an existing manhole about 50 metres from the house and considerably lower than the house. I believe that I will have to install one or more back drop manholes to get the gradients right. I have a couple of questions about this:

1. Can I use the new deeper non-man entry inspection chambers to get a drop of, say, 2 metres in one go or would this be considered too narrow? If it’s too narrow, would I have to build a larger brick or concrete inspection chamber? (In fact, can I use the plastic inspection chambers for back drop manholes at all, or do they always have to be brick or concrete?)

2. If the vertical drop is less than 1800mm, I have read that I should have a 45 degree slope down into the bottom of the chamber rather than a vertical drop. If I do this, how do you rod the section that is at the 45 degree slope? None of the pictures that I have seen show a rodding access point at the top of this slope. (Or do you do it from the bottom?)

3. I presume that there are rules on how deep drains must be laid but I can find them. Is there a minimum depth? Obviously, the higher up the manhole I can put the entry point, the greater the drop that I can achieve with each one. (All of the drains will be within our garden.)

Thanks for your help.

AA

 

[noseall]

Fitting a drop pipe involves using a 90 degree junction instead of a 90 degree bend at the point where it turns down into the manhole. This is so that the pipe is roddable.

The bottom of the drop should have a 45 degree turn so that the foul water is directed toward the flow of the manhole.

I would imagine that after say 1.2m deep a 480mm (dia) plastic chamber becomes redundant.

http://images.google.co.uk/imgres?i...=/images?q=manhole+drop+pipe&gbv=2&hl=en&sa=X

 

[Hugh Jaleak]

Probably be down to your B.C.O. and what he'll allow, but ive seen some fairly deep backdrops before.

I dont think you are allowed to go much more than a metre deep with the 450mm dia chambers, however using a 450mm dia base, surrounding it with concrete, and benching to the plastic, then coming up with concrete rings is an option ive seen used frequently on new builds.

This may be of some help to you.
http://www.pavingexpert.com/drainage.htm

 

[aa44]

Thanks very much.