Vibro Stone Columns

[Rambro]

Does anyone have some good design references/procedures for vibro stone columns? It would be nice if calculations were included.

Thanks for the help,

 

[MTNClimber]

99% of the time the contractor does that in house but either way, please use the search function.

[URL unfurl="true"]https://www.eng-tips.com/viewthread.cfm?qid=458147[/url]

 

[oldestguy]

See if you can find anything by the VibroFlotation company.

 

[Mad Mike]

I've attached an article on the engineering principles of Control Modulus Columns (CMC), which are a modern day alternative to the old vibro-stone columns. Many of the principles still apply.

I don't know what soils you're up against, but in my area the old stone columns have been entirely superseded- very few contractors are able to install them to satisfaction...if the soil conditions aren't clearly defined there is a risk of poor performance and serious cost overruns, particularly with very soft clays where the vibro stone extrudes into the surrounding clays.

I'd recommend that you run your proposal past an experienced contractor at an early stage of design- there may be serious limitations that you're not aware of.

All the best,
Mike

 

[EireChch]

Mad Mike - vibro stone columns are perfect for soft clay. Extruding into the surrounding soil is the point. You improve soft clay by increasing the horizontal stress thus increasing Ko.

Vibro stone columns are generally designed using the Priebe 1995 method. This determines you post stone column settlement. You can find it online. Essentially you work out an improvement factor n (generally around 2-3, lets assume 3)which is based on your area replacement, column friction angle, column modulus and the ratio of column modulus to existing soil modulus. Your original settlement (i.e. say 120mm without stone columns) is reduced by the factor n. Your post stone columns settlement is 120 / 3 = 40mm.

 

[Mad Mike]

Thanks EireChch- I'd always been wary of the long-term performance in very soft clays...really appreciate your feedback.

Cheers,
Mike

 

[Guest262653]

Priebe's method is what I've seen being used in vibro stone columns projects here in Europe. I have never been involved in the final design of any of these projects as the contractors usually have their own in-house technical staff that develops their solutions, but some years ago I did a feasibility study and a couple of preliminary design calculations using Priebe's method for the foundation of large chemical tanks.

I programmed a simple spreadsheet as a study aid and the results were ok when compared with some design examples and software but it was never really tested with a real project. I enclose it to this post as it may help someone get into the method but please be aware that it may contain mistakes. Use it as you wish.

The original papers by Priebe are probably easy to find on Sci-hub.

 

[Rambro]

Thanks everyone for the great posts and links so far! asvcorreia: that's much more than a "simple" spreadsheet!

 

[Rambro]

In my market the typical application is in 10' to 20' surficial urban fill. It's a no-brainer when it's clean and relatively dense we have used area replacement ratio's as low as 12%. I get particularly uncomfortable with organics and peat layers. Any insights in adding grout or somehow sleeving (ie: geotextiles) in these conditions would be appreciated.

 

[EireChch]

Geotextile encased stone columns can be used in peat / organics. I have not heard of adding ground combined with SC. That would be getting more into the CMC columns.

There is not much technical requirements when it comes to stone column design. The software that is used i.e. Kellers in house software is just the Preibe method. I have seen this a few times. You can do a stone column design on 1 A4 page with a hand calc.

The key thing is the onsite trials first to find your best grid layout then the verification with zone load tests, CPTs, plate load tests on top of columns. This is where the contractors practical experience is far superior to the consultants.

 

[pelelo]

Use FHWA GRound improvement volume.

There are examples