Liquefaction mitigation with Geopiers 1

[BDBCRUZ]

I am working on a site along a creek. The soil at the site consists of alluvial deposits. There is a free face along the creek. A liquefiable layer exists at between roughly 12 and 18 feet below grade. The liquefiable soil is mostly SM and SP with SPT blow counts generally between 5 and 12. The overlying soils are generally SM and ML with SPT blow counts generally ranging between 5 and 18. The liquefiable sand layer is underlain by 2 to 3 feet of gravel (possibly liquefiable) then sandstone. Our preliminary analysis indicates that the site could laterally spread during an earthquake. It is proposed to construct a 3 story structure with lower floor parking (partially). We are considering using geopiers for ground modification at this site. Do any of you know of a study, or other literature, regarding geopiers and liquefaction - lateral spreading mitigation? Have any of you succesfully used geopiers to mitigate liquefaction and/or lateral spreading in a similar environment? Any words of wisdom would be appreciated.

 

[GeoPaveTraffic]

I have worked with GeoPier for projects in the past. However, none of the sites were liquifiable. What does the technical support group at GeoPier have to say?

 

[BDBCRUZ]

I have sent my prelimary logs and other pertinent data to GeoPier for their review. Their initial feedback indicates that geopiers would be an applicable procedure for mitigating liquefaction at the site but I am looking for third party feedback and independent studies.

 

[CarlB]

I don't know about GeoPiers, but a similar technique, Sand Compaction Piles, is used extensively in Japan for soil densification/liquefaction mitigation. See

http://www.fudo.co.jp/english/corebusiness.html

for some general info.

 

[born2drill]

Vibro stone columns, by whatever name you want to call them, can be used to mitigate liquefaction potential. I don't see why a Geopier system wouldn't work fine.

A general note of caution - I find that suppliers of proprietary products will almost always tell you that their proprietary product will fix your problem. Good for BDBCRUZ for doing his homework.

 

[GeoPaveTraffic]

Born2drill,

In general I agree with you. However, in this case I know and have worked with the main technical person for GeoPier US. If the product that he supports will not work, he WILL tell you. Also, his PHD was on liquifaction.

 

[Geocontractor]

BDBCRUZ,

I have a link to a website for vibropiers/stone columns/whatever that have been used for liquifaction.

 

[Geocontractor]

If you go to

http://www.haywardbaker.com/services/vibro_replacement.htm

there is information regarding the installation of vibro-stone columns to mitigate liquifaction. If you register on the site, you can also download/view project summaries on projects completed with this technology. Hope this helps.

 

[dgillette]

Let me advocate caution in using geo piers or stone columns for mitigating liquefaction potential.

1. The usual design intent of stone columns is densification, and they work well for that in clean sands. You note ML soils, which will generally not respond well to densification because of their low permeability. Depending on fines content, SM may not do so well either. This is the source of one of our current headaches.

2. If you are considering them for reinforcement, look at the mechanics involved as if you were a structural engineer looking at weak beams. Are you relying on slender elements to provide lateral resistance? If so, I don't think you can estimate their resistance by a simple area replacement ratio because of bending. This isn't like a simple shear test on a sample with the dimensions of a hockey puck.

Stone columns HAVE worked well on level ground for minimizing settlement, but there isn't much in the way of field performance info for lateral loads.