TANK SETTLEMENT FORECAST. 2

[Mselva1]

Hi:

We are evaluating build four tanks (diameter= 150', height= 50'). Since the soil is very bad, the best solution after add aggregates, envisages a 10" settlement over the time. The foundations with piles represents a high cost solution.

I will appreciate your comments about how deal with this kind of settlements, mainly with the pipelines attachments.

Best Regards,

 

[fegenbush]

Plan for the tank foundation to have additional projection to account for the anticipated settlement and use flexible piping connections that will withstand the vertical displacement.

 

[SlideRuleEra]

Two couplings that allow for angular deflection along with a length of pipe between them will allow for settlement. Here is a paper giving a general information about this:

http://tps.us/images/upload/file/Instructions and Specs/Installation Guidelines for Piping 2.pdf

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[JedClampett]

Can you presettle the soil by applying fill to it? How much time is the settlement exspected to take?

 

[BigH]

Can Mselva1 detail the soil stratigraphy and any layer properties? JC has a good idea - but use of wick drains (or sand drains) to speed up the settlement and thereby reduce the preload/surcharge time would be beneficial. Always use flexible connections as suggested - even if settlements are expected to be small (50 mm or so) as rigid piping is not forgiving. Thanks for the reference SRE - good to see you back!

 

[Mselva1]

Thank all of you for your answers. The use of pre-loads it is not feasible because the time. We are in a hurry with this project. I think the use of flexible connection it can work but I had doubts about how much is possible to cover with these kind of elements.

Enclosed you will find one of the geotechnical surveys (in Spanish, but numbers are numbers).

Thanks again for your help.

 

[GeoPaveTraffic]

Interesting, my Spanish stinks but I believe I figured the log out.

I expect that most of the computed settlement is in the Organic clay between elevation 82.3 and 87.0 m. It might be wothwhile to talk to the geotechnical about how much of the settlement is elastic versus consolidation. The eleastic portion will go up and down as the liquid level in the thank changes. Over time that could cause problems for the flexible connectors. Not likely, but worth checking into.

Mike Lambert

 

[FixedEarth]

You can use drilled piers to reduce your settlement and not to support your mat foundation. So for example, you can replace 25% of your foundation plan area with 0.5m to 1.0m diameter drilled pier filled with grout or concrete and having a length of about 15 m. This should reduce your settlement approximately by about a third to a half. I am getting about 8 inch settlement (assumed induced pressure of 75 kPa) & this solution may get you down to about 5 inch total settlement. See attached.

 

[BigH]

PVD wick drains are quick to install and can be used during the water testing if the water testing is done slowly with a view to building out settlement - as you said that you have "no time" for proper preload (even, I presume, with wick or sand drains). Then after settlement dissipates, you can do the connections.

 

[IFRs]

In some parts of the world, settlement is an assumed fact of life. The tank foundations have notches to allow periodic jacking of the tank and re-grouting underneath. Piping is designed for flexibility, settlement is monitored, tanks are jacked when needed. There are solutions for most but not all settlement problems. It is costly, requires good planning, careful monitoring and money set aside for future adjustments. Of course, this is in locations that care about the environment and do not happily sacrifice future generations to achieve a profit today. Let's try not to let the excuse of no time be used to force a construction project forward that may wind up being more costly or damaging to the environment than it should be.