Hollow Stem Auger versus Mud Rotary (Beach Sand) (Part #2) 1

[pelelo]

thread274-464299

Engineers,

Referencing this previous thread, I do understand the shortcomings of using HSA on sands, below the GWT.

I have spoken with several drillers from the "HSA school" and they told me that in order to overcome the "live sand" or heave effect, they add water inside de augers in order to reach equilibrium. According to them, they don't have any type of issues when performing SPT tests.

Another driller told me he has used bentonite inside the casings (instead of water) to overcome the heave effect.

Please let me know your thoughts.

 

[GeoPaveTraffic]

When drilling in sands below the water table, mud rotary drilling should always be used. Adding water or even drilling mud to hollow stems augers sometimes works, but many times it does not. Why take the risk. Just do it right by switching to mud rotary drilling.

Mike Lambert

 

[pelelo]

Thanks GeoPaveTraffic.

Do you by chance have a good reference that could provide information about these shortcomings using HSA's?.

On other note, this problem is only using HSA's under water table in coastal plain soils (clean sands). For any other situations (e.g residual soils or any type of fill using mixed soils (e.g SC, SM, etc)), the HSA would not be an issue?, do you agree?.

 

[GeoPaveTraffic]

This is a problem for any clean sand below the water table. The orgin of the sand does not matter.

As for a reference, I don't have anything in front of me. However, i expect that any text book that discusses drilling technices will include a similar discussion.

If you are hiring the driller for a project, then just tell them up front that when drilling in sands and the water table is encountered; that they will be required to switch to mud rotary. If they don't want the work, then find a different driller. I've had to do this a time or two, but most drillers will happily switch when you tell them it is that or they don't get the work.

Mike Lambert