Geopiers thread261-64135

[BigEasyGeoSleuth]

For geopiers in the GWT: How effective can the ramming action be insofar as to densification and/or increase lateral stress below the groundwater table (skeptical)? Also, does anyone know if geopiers can take lateral loads?

 

[casimmons]

Yes, geopiers can be effective below the water table, depending on the soil type. However, keep in mind that the presence of water makes construction is more difficult- casing the holes will likely be needed and open graded stone backfill is necessary.

Geopiers don't really "take" lateral loads, but they can provide increased sliding resistance due to the higher base friction of the aggregate compared to that of the site soil.

 

[garrettk]

There are two types of geopiers - one in which aggregate is rammed into a predrilled hole and a second that is rammed into the soil with no predrilling. I've seen several presentations about geopiers at conferences but have never used them myself. The one project I worked on where they were recommended was never constructed.

The piers that are rammed into the soil with no predrilling will have provide some densification of the surrounding soils as they are basically displacement piers; however, the actual "lateral load capacity" would still be basically zero. They are intended to provide improvement in vertical bearing capacity - not lateral capacity.

 

[mudman54]

please consider dewatering before trying to compact aggregate below the water table

 

[sunny7uc]

You do not ned to worry abour water table, use some other aggregate pier system like Vibro Piers. It can be installed by dry bottom feed method. Checkout

http://www.vibropiers.com

or

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

 

[COEngineeer]

I have heard that they can also put a steel rod in the middle to provide uplift capacity for lateral design.

Never, but never question engineer's judgement

 

[sunny7uc]

You can put a steel rod in the center or do a soil anchor between columns for uplift. Uplift capacity can be provided with any aggregate-pier system. Check out FAQs at the above refernced website.