Differential Settlement Connections

[msquared48]

Got a problem here in that I have a large concrete detention vault on piling to design on a site that could see 18 to 24" of long term settlement.

Does anyone have any flexible connection details for stormwater pipe into and out of the vault, plus water and sewer for the same situation, that they could share?

Any input would be appreciated. Thanks all.

Mike McCann
MMC Engineering

 

[msucog]

wow...sounds like an extrodinarily tough site. i don't have details to provide but would be interested (if you can disclose such info) to know more about the particular site and planned construction. perhaps something could be done to offset the differential (depending on the site conditions that is). if you can't/won't disclose details, i completely understand...again, your site simply sounds very interesting.

 

[rconner]

Joining structures available with appropriate lengths of ductile iron pipe offer considerable strength and deflection, along with some axial extension, capabilities if needed (e.g. see ball joints at

http://www.acipco.com/adip/pipe/ball/flbj.cfm).

Where great movment is expected to occur e.g. geologically hazardous areas, I have even heard suggested various techniques of "trench softening" and/or encasements of pipes e.g. with loose polyethylene sleeves etc. to minimize relative loadings. 18"-24" of (vertical, relative?) movement sounds like a lot of variation in invert as some of these sound like gravity pipes; therefore, if you have not done so you probably would want to check to make sure water will flow the way you need it to throughout all range of movement/service life etc.!

 

[msquared48]

muscog:

This is a site with a five story wood frame condo on a PT podium slab with parking under, all resting on a pile foundation, piles extending up to 75 feet into an old flood plain outwash area. Bottom line is real lousy material leading to large differential settlements. These settlements are trying to be mitigaged with preloading the site, but the geothech has to finalize the figures yet. This is the worst case scenario and I want to pin down my options here.

I don't think drainage out of the detention tanks will be a problem, but going in, that's another matter to consider. My buddy's doing the Civil site drainage, but I'm doing the tank. As you said, it's going to be interesting to say the least. The water table elevation will be an interesting issue too.

Mike McCann
MMC Engineering

 

[LittleWheels]

I was vaguely involved with an underground coal mine workface under a motorway with very large settlements expected and observed

http://news.bbc.co.uk/2/hi/uk_news/england/1608898.stm

We had some interesting problems with keeping services working, drains were flowing the wrong way at times.

 

[rconner]

Normally I like flexbility in underground systems, but if inverts must be maintained in very bad soils, perhaps sometimes supporting basically everything uniformly on piles may be appropriate (e.g. see

http://www.dipra.org/pdf/pipeOnSupports.pdf)

 

[civilperson]

Try longitudinal pipe supports with 24" depth void forms under the pipe cradle.